Environmental Humidity Energy Harvester

Abstract

A solid-state energy harvester, including an anode that includes a first transition metal suboxide; a cathode that includes a second transition metal suboxide; and a separator interposed between the anode and the cathode; wherein at least one of the anode, the cathode or the separator contains water; and wherein the harvester produces electricity when electrically connected to an external load.

Description

BACKGROUND

Energy harvesters are devices that do not store energy, but rather gather it from the environment. See, e.g., U.S. Pat. Nos. 8,115,683; 10,147,863; 10,142,125; and 10,141,492. For example, energy harvesters gather energy from a variety of sources (e.g., solar power, thermal energy, wind energy, salinity gradients, kinetic energy, piezoelectric, pyroelectric, thermoelectric, and RF-capturing devices like the crystal radio). Some are very high-energy generators, such as wind and solar, and some are very low energy output such as the piezoelectric or RF harvesters. These energy harvesters, however, do not store energy, but rather harvest it from their surroundings.

There have been recent efforts to make a battery using only electrons to transfer charge rather than ions. Sigler, D., “All-Electron Battery—Stanford Strikes Again,” CAFE Foundation (Mar. 28, 2015) (cafe.foundation/blog/electron-battery-stanford-strikes). However, these devices store rather than harvest energy.

Thus, there is a need for energy harvester devices that use solid-state electrolytes to generate on-demand energy from the surrounding environment for a variety of applications.

All metal oxides have integer valences. A transition metal suboxide is a metal oxide with some of the oxygens in the crystal structure missing, giving the appearance of a non-integer valence of the metal atom.

SUMMARY

Aspects described herein provide solid-state energy harvesters, comprising a first current collector comprising a conductor, a first layer comprising a first transition metal suboxide and a second transition metal suboxide, wherein the first layer is an anode and in contact with the current collector, a second layer in contact with the first layer, wherein the second layer is a separator, and a third layer comprising a third transition metal suboxide and a fourth transition metal suboxide, wherein the third layer is a cathode, and is in contact with the second layer and a second current collector, and wherein the second layer forms a separator layer between the first and third layers.

It is understood that the solid-state energy harvesters described herein can optionally be configured to store energy or can be coupled with an energy storage device.

Further aspects provide solid-state energy harvesters, comprising a first current collector comprising porous carbon fiber, filaments, powder or paper, and conductor, a first layer comprising a first transition metal suboxide and a second transition metal suboxide, wherein the first layer is an anode and in contact with the current collector, a second layer in contact with the first layer, wherein the second layer is a separator, and a third layer comprising a third transition metal suboxide and a fourth transition metal suboxide, wherein the third layer is a cathode, and is in contact with the second layer and a second current collector, wherein the second layer forms a separator layer between the first and third layers, and wherein the solid-state energy harvester produces current in a presence of oxygen and water vapor.

In other aspects, methods of making a solid-state energy harvester comprise grinding an anode mixture comprising a first transition metal suboxide, a second transition metal suboxide, and a binder, grinding a cathode mixture comprising a third transition metal suboxide, a fourth transition metal suboxide, and a binder, admixing a carbon powder to each of the anode mixture and the cathode mixture, forming the anode mixture into a first layer, wherein the first layer is an anode, forming a second layer, wherein the second layer is a separator, forming the cathode mixture into a third layer, wherein the third layer is a cathode, and connecting the first layer to the second layer and the second layer to the third layer, wherein the first transition metal suboxide and the third transition metal suboxide are different from each other.

In some aspects of the method, the anode mixture and the cathode mixture are ground in a high-shear, high intensity blender for at least one minute. The binder may be a Teflon binder, preferably comprising poly (1,1,2,2 tetrafluoroethylene), and the binder may be about 40 volume percent of each of the first layer and the third layer. In some aspects, the first layer, the second layer, and the third layer are formed by compression in a roller mill to produce a back-extrusion. The anode mixture preferably comprises about 83% nTi₄O₇, 17% nWO_2.9, 40 volume percent binder (powder), and 2% nano-sized acetylene carbon black powder, preferably Vulcan XC 72R or Nano 307. In some aspects, wherein the cathode mixture comprises about 70% nWO_2.9, 30% Co₃O₄, 40 volume percent binder (powder), and 2% nano-sized acetylene carbon black powder, preferably Vulcan XC 72R or Nano 307. Alternatively, the cathode mixture may comprise about 72% nWO_2.9 and 28% Co₃O₄, 40 volume percent binder (powder). In some aspects, the second layer includes a hydrated, non-plasticized cellophane and a proton exchange membrane, or a silver-filled hydrated, non-plasticized cellophane.

In some aspects of the method, the anode mixture comprises about 83% nTi₄O₇, 17% nWO_2.9, 40 volume percent binder (powder), and 2% nano-sized acetylene carbon black powder, preferably Vulcan XC 72R or Nano 307; the second layer comprises one of hydrated, non-plasticized cellophane and a proton exchange membrane; and the cathode mixture comprises about 70% nWO_2.9, 30% Co₃O₄, 40 volume percent binder (powder), and 2% acetylene nCarbon Black (Cabot V72).

In another aspect of the method, the anode mixture comprises about 83% nTi₄O₇, 17% nWO_2.9, 40 volume percent binder (powder), and 2% nano-sized acetylene carbon black powder, preferably Vulcan XC 72R or Nano 307; the second layer comprises one of hydrated, non-plasticized cellophane or a proton exchange membrane; and the cathode mixture comprises about 72% nWO_2.9, 28% Co₃O₄, 40 volume percent binder (powder), and 2% nano-sized acetylene carbon black powder, preferably Vulcan XC 72R or Nano 307. Each of the first layer and the third layer preferably comprise Teflon particles, the binders comprise powders, and each of the first layer and the third layer is made using a roller mill to force extrude the powders through rollers of a mill, and to extrude the Teflon particles into fibrils. In an aspect of the method, the step of forming the anode mixture into a first layer includes forming an anode disk and grommet assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary crystal structure of cerium dioxide.

FIG. 2 shows an exemplary cerium reduction mechanism.

FIG. 3 illustrates how oxygen dissolves in water.

FIG. 4 illustrates the effects of dehydration on the crystal structure of tungsten suboxide WO_2.9.

FIG. 5 shows an exemplary crystal structure of cobalt suboxide, a.k.a. cobalt(II,III) oxide (Co₃O₄).

FIG. 6 shows an exemplary crystal structure of Ti₄O₇.

FIG. 7A shows an exemplary physical layout of an aspect of a solid-state energy harvester with multiple layers of expanded metal between electrodes.

FIG. 7B shows an exemplary physical layout of a six-electrode energy harvester.

FIG. 8 illustrates the use of a rolling mill to make a rolled electrode.

FIG. 9 is a graph showing an exemplary current density during shorting of an energy harvester.

FIG. 10 is a graph showing an exemplary recovery of an energy harvester after shorting.

FIG. 11 is a graph showing the exemplary results of a non-discharging energy harvester in oxygen, argon (0% oxygen), and air after shorting recording the Open Circuit Voltage (OCV).

FIG. 12 is a graph showing an exemplary shorted current density in air, oxygen and argon (0% oxygen).

FIG. 13 is a graph showing an exemplary Voltammogram for a dead-shorted energy harvester after 48 hours rest in air.

FIG. 14 is a graph showing the AC impedance of an exemplary solid-state energy harvester.

FIG. 15 is a graph showing a Nyquist plot of an exemplary solid-state energy harvester.

FIG. 16 shows an exemplary solid-state energy harvester with nickel expanded metal between all electrodes.

FIG. 17 is a graph showing a Voltammogram for an exemplary solid-state energy harvester.

FIGS. 18A and 18B are graphs showing shorted discharges and open circuit voltage (“OCV”) spontaneous recharges for an exemplary solid-state energy harvester.

FIG. 19 is an illustration of an exemplary 3-layer thin-film solid-state energy harvester.

FIG. 20 is a Voltammogram of an exemplary solid-state energy harvester.

FIG. 21 is a graph showing a long Open Circuit Voltage (OCV) of an exemplary solid-state energy harvester.

FIG. 22 is a cross-section of an exemplary solid-state energy harvester.

FIG. 23 is a graph showing current density for three 24-hour tests of an exemplary solid-state energy harvester.

FIG. 24 is a graph showing OCV recovery after three tests of an exemplary solid-state energy harvester in different environmental gasses including air, oxygen and the inert gas argon (0% oxygen).

FIG. 25 is a graph showing OCV between the tests showing the OCV recovery rates in three different gas environments (Oxygen, Air and (0% oxygen)).

FIG. 26 is a graph showing dead-short discharges for the life of an exemplary solid-state energy harvester.

FIG. 27 is a graph showing long discharge over eight days of an exemplary solid-state energy harvester.

FIG. 28 is a graph showing the effect of adding oxygen or argon (0% oxygen) or air (20% oxygen) to the test chamber during energy harvester discharge of an exemplary solid-state energy harvester.

FIG. 29 is a graph showing impedance as a function of current density as an exemplary solid-state energy harvester humidifies to water-saturated conditions.

FIG. 30 shows the limiting current taken from the Voltammograms of three exemplary energy harvester designs.

FIG. 31 shows the general electron flow of an exemplary energy harvester.

FIG. 32 shows an exemplary three-layer cell design with an anode (A), separator (Sep), and cathode (C).

FIG. 33 shows power density curves with the addition of graphite to the anode and cathode in the three-layer cell design compared to a two electrode design without the addition of graphite to the anode and cathode and after shorting for 24 hours then open circuit voltage (OCV) recovery.

FIG. 34 shows power density during dead short discharge is increased by about 10-fold in the three-layer design with carbon added to the electrodes compared to a two electrode design without carbon added to the electrode.

FIG. 35 shows 100 mV discharge in air, oxygen, argon, and argon over a 24-hour period in the three-design with carbon added to the electrodes.

FIG. 36 shows the power curve for three exemplary designs as labeled: a power curve for a two-electrode design containing no carbon, a three-electrode design one with 3% nano graphite added to the anode and cathode and an SSE layer between the anode and cathode, and a three-electrode design with 3% Vulcan 72 carbon black added to the anode and cathode with a SSE layer between the anode and cathode.

FIG. 37 shows performance improvement using an exemplary three-electrode design with gold-plated current collectors, nano-size powder and carbon additive.

FIG. 38 shows performance improvement from the three-electrode design of FIG. 37 showing the first derivative of the polarization curve. and

FIG. 39 shows the results of an exemplary experiment showing the effects of relative humidity (RH) on current output.

FIG. 40 shows cell specific current density of the exemplary active components (Ti₄O₇ and Co₃O₄) with and without the exemplary solid state electrolyte (SSE) separator (CeO₂ and WO_2.9).

FIG. 41 shows the results of an exemplary study of cell power density as a percentage of the maximum cell power with varying electrode thickness.

FIG. 42 shows an exemplary five-layer cell design with an anode, separator, and cathode, inside a cell body.

FIG. 43 is an elevational view of a polypropylene gasket for use in manufacturing an exemplary cell.

FIG. 44 is a 3D CAD view of a holder for a tester for use in manufacturing an exemplary cell.

FIG. 45 is a cross-sectional view of the holder of FIG. 44.

FIG. 46 shows a chemical mechanism of an exemplary cell.

FIG. 47 shows the anoxic cell of Example 22 in exploded view.

FIG. 48 shows the anoxic cell of Example 22 in cross section after loose assembly.

In use, the parts are compressed together.

DETAILED DESCRIPTION

The disclosed methods, compositions, and devices below may be described both generally as well as specifically. It should be noted that when the description is specific to an aspect, that aspect should in no way limit the scope of the apparatus or methods. The feature and nature of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the accompanying drawings.

Aspects described herein provide a solid-state energy harvester, comprising a first current collector comprising a highly conductive solid sheet such as gold plated brass.

A first layer of the energy harvester can have a first transition metal suboxide, and a solid-state electrolyte (SSE) wherein the first layer is an anode and is in contact with the first current collector.

A second layer can have an admixture of a second transition metal suboxide, and a lanthanide oxide or dioxide, wherein the admixture forms a solid-state electrolyte (SSE) and is in contact with the first layer.

A third layer of the energy harvester can comprise a third transition metal suboxide, wherein the third layer is a cathode and is in contact with the second layer and in contact with a porous carbon fiber, a filament, a powder or a paper current collector.

The first transition metal suboxide can be selected from the group consisting of tungsten suboxide, cobalt suboxide, Na_1.0Mo_1.5WO_6.0, Na_0.9Mo₆O₁₇, Na_1.0Ti_1.5WO_4.5, Na_1.2 Ti_0.34WO₄, Ti₄O₇, Ti₅O₉, K_1.28Ti₈O₁₆, K_1.04Ti₈O₁₆, K_0.48 Ti₈O₁₆, Na₄WO₃, Na_0.90WO_1.81, Na_0.82WO_1.81, Na_0.74WO_1.81, K_0.9WO₃, WO_2.72, WO_2.82, WO_2.9, Na₂WO₄, Na_8.2WO, Na₂O₂WO₃, Na_1.2Ti_0.34WO₄, Na_1.2Cu_0.31WO_7.2, Na_1.2Mo_0.31WO_5.2, and Na₂O₄WO₃.

The third transition metal suboxide can be selected from the group consisting of tungsten suboxide, cobalt suboxide, Co₃O₄, Na_1.0Mo_1.5WO_6.0, Na_0.9Mo₆O₁₇, Na_1.0Ti_1.5WO_4.5, Na_1.2Ti_0.34WO₄, K_1.28Ti₈O₁₆, K_1.04Ti₈O₁₆, K_0.48 Ti₈O₁₆, Na₄WO₃, Na_0.90WO_1.81, Na_0.82WO_1.81, Na_0.74WO_1.81, K_0.9WO₃, WO_2.72, WO_2.82, WO_2.9, Na₂WO₄, Na_8.2WO, Na₂O₂WO₃, Na_1.2Ti_0.34WO₄, Na_1.2Cu_0.31WO_7.2, Na_1.2Mo_0.31WO_5.2, and Na₂O₄WO₃.

The energy harvester can optionally include other suboxides, for example, the following: ReO₃, Na_0.9WO₃, Na_0.9WO₃+TiO, Na_0.9WO₃+MoO₂, Na_1.0 WO₃, Na_1.1WO₃, Na_0.83 WO₃, Ti₄O₇, Co₃O₄, CeO₂, potassium titanium oxide (K_1.28Ti₈O₁₆), KI, and KCl. The anode may optionally include Na_0.9W_0.75Ti_0.25O₃ and the cathode may optionally include Na_0.9W_0.75Cu_0.25F_0.3O_2.8.

The first transition metal suboxide, second transition metal suboxide, or third transition metal suboxide can be selected from the group consisting of boron, iron, copper and nickel suboxides.

In a further aspect, the first transition metal suboxide is an alkaline metal suboxide (e.g., rubidium and caesium suboxides).

The lanthanide oxide can be selected from the group consisting of cerium dioxide, lanthanum oxide or dioxide, praseodymium oxide or dioxide, neodymium oxide or dioxide, promethium oxide or dioxide, samarium oxide or dioxide, europium oxide or dioxide, gadolinium oxide or dioxide, terbium oxide or dioxide, dysprosium oxide or dioxide, holmium oxide or dioxide, erbium oxide or dioxide, thulium oxide or dioxide, ytterbium oxide or dioxide, and lutetium oxide or dioxide.

In yet another aspect, the first transition metal suboxide is Ti₄O₇. In one aspect, the second transition metal suboxide is WO_2.9. In another aspect, the third transition metal suboxide is Co₃O₄. In a further aspect, first layer and the third layer do not substantially comprise noble metals.

In one aspect, the first layer, second layer and the third layer each further comprise a binder (e.g., unsintered Teflon (PTFE), FEP, Paraffin and epoxy).

The anode can comprise between about 0.01% and about 14% water. The cathode can comprise between about 0.01% and about 4% water.

In a further aspect, the first transition metal suboxide, the second transition metal suboxide, and the third transition metal suboxide each have a stoichiometry M_x-y, wherein:

• • M is a transition metal M,
  • x is base valence value of the transition metal M,
  • y is deviation from unity, and
  • when M is titanium, x is 4 and y is at least 0.5,
  • when M is cobalt, x is 3 and y is at least 0.3, and
  • when M is tungsten, x is 5 and y is at least 0.2.

The conductor can comprise a metal comprising gold, nickel, copper, brass, bronze, or porous carbon fiber.

In one aspect, the porous carbon fiber comprises greater than about 50% pores, alternatively greater than about 55%, 60%, or 65% pores. In another aspect, the pores have a diameter from about 10 μm to about 40 μm, alternatively 15 μm to about 35 μm, or 20 μm to about 30 μm.

In a further aspect, the current collector comprises a foamed metal.

In one aspect, the solid-state energy harvester includes a first current collector containing a conductor; a first layer comprising a first transition metal suboxide and a second transition metal suboxide, wherein the first layer is an anode and in contact with the current collector; a second layer in contact with the first layer, wherein the second layer is a separator comprising a cellulosic; a third layer comprising a third transition metal suboxide and a fourth transition metal suboxide, wherein the third layer is a cathode, and is in contact with the second layer and a second current collector comprising porous carbon paper in contact with the third layer; and a fine stainless steel screen in contact with the porous carbon paper and forming the second (cathode) current collector. Preferably, the first transition metal suboxide includes Ti₄O₇, the second transition metal suboxide includes WO_2.9, the third transition metal suboxide includes Co₃O₄, and the fourth metal suboxide comprises WO_2.9. The second layer may includes a hydrated, non-plasticized cellophane and a proton exchange membrane, or a silver-filled hydrated, non-plasticized cellophane, or a Nafion (sulfonated tetrafluoroethylene based fluoropolymer-copolymer of formula C₇HF₁₃O₅S·C₂F₄). Preferably, the thickness of at least one of the first layer and the third layer is from about 0.25 mm to about 1 mm, more preferably about 0.7 mm. The conductor preferably includes gold, nickel, copper, brass, bronze, or porous carbon fiber. The current collector preferably includes a foamed metal. In an aspect, the solid-state energy harvester produces current in a presence of oxygen and water vapor. In an aspect, the second current collector comprises a stainless-steel screen. In an aspect, the harvester is in the form of a cell assembly including the following layers: a cathode current collector; a cathode disk and grommet assembly; a cellulosic disk; an anode disk and grommet assembly; and a gold-plated brass disk.

Aspects described herein provide a solid-state energy harvester system, comprising a first energy harvester and a second energy harvester, wherein the first energy harvester and the second energy harvester comprise the solid-state energy harvester as described herein, and wherein the first layer of the first energy harvester is in electrical connection to the third layer of the second energy harvester. The first layer of each of the first and second energy harvesters can comprise titanium suboxide and the third layer of each of the first and second energy harvesters can comprise cobalt suboxide.

Further aspects provide a solid-state energy harvester, comprising a current collector comprising a solid metallic current collector (e.g., gold-plated); a first layer comprising a first transition metal suboxide, and a solid-state electrolyte (SSE) wherein the first layer is an anode and in contact with the current collector; a second layer comprising an admixture of a second transition metal suboxide, and a lanthanide oxide or dioxide, wherein the admixture forms a SSE and is in contact with the first layer; and a third layer comprising a third transition metal suboxide, wherein the third layer is a cathode and is in contact with the second layer, the anode, and a current collector comprising porous carbon fiber, filaments, powder or paper, wherein the solid-state energy harvester produces current in a presence of oxygen and water vapor.

In one aspect, having the exemplary solid-state energy harvester in the presence of water vapor and/or increased relative humidity (RH) can improve the current density produced by the exemplary solid-state energy harvester. In contrast, it is believed that liquid water can reduce the current density produced by the exemplary solid-state energy harvester. In some instances, the solid-state energy harvester can have an internal water supply configured to increase the relative humidity surrounding the solid-state energy harvester.

Without being bound by theory, it is believed that water dissociation of the surface adsorbed water molecules produces hydroxyl's (OH⁻) and protons (H⁺) and the protons are the internal charge-transfer element.

In one aspect, the electrochemical flow for the anode can be H₂O+TiO_x→TiO_xOH⁻+H⁺→TiO_x+½O₂+H⁺+2e⁻ or simplified to H₂O—TiO_x→½O₂+2H₊+2e⁻. In this aspect, the electrons pass through an external circuit to the cathode.

In one aspect, the electrochemical flow for the cathode is 2CoOx+2H++2e⁻→2CoO_x+H₂ or simplified to 2H⁺+2e⁻—CoO_x→H₂.

Without being bound by theory, it is believed that the exemplary solid-state energy harvester may be exhaling oxygen from the anode and hydrogen from the cathode.

In one aspect, the moisture uptake of exemplary compounds used in the solid-state energy harvester is CoO₂>Ti₄O₇>>Co₃O₄>WO_2.9.

In some instances, the first transition metal suboxide comprises Ti₄O₇, the second transition metal suboxide comprises Co₃O₄, and the SSE comprises CeO₂ and WO_2.9.

In some instances, the thickness of at least one of the first layer, second layer and the third layer is from about 0.25 mm to about 1 mm.

In some instances, the thickness of at least one of the first layer, second layer and the third layer is about 0.7 mm, alternatively 0.5 mm to 0.9 mm or 0.6 mm to 0.8 mm.

In some aspects, the current density produced by the solid-state energy harvester in a relative humidity of 85% is 45% to 55%, alternatively about 50%, of its maximum current density at 100% RH.

Methods of making a solid-state energy harvester are also provided. Exemplary methods comprise (1) grinding a solid-state electrolyte (SSE) comprising a lanthanide and the second transition metal suboxide, and a binder; (2) grinding an anode mixture comprising a first transition metal suboxide, the SSE and a binder (3) grinding a cathode mixture comprising a third transition metal suboxide, the SSE and a binder; (4) admixing a carbon powder to each of the anode mixture, the and the cathode mixture; (5) forming the anode mixture into a first layer, wherein the first layer is an anode; (6) forming the SSE mixture into a second layer, wherein the second layer is an SSE separator; (7) forming the cathode mixture into a third layer, wherein the third layer is a cathode; and (8) connecting the first layer to the second layer and the second layer to the third layer wherein the first transition metal suboxide, the second transition metal suboxide and the third transition metal suboxide are different from each other.

Without being bound by theory, it is believed that performing step 4 (admixing a carbon powder) following the grinding steps (2) and (3) unexpectedly results in improved performance as described in Example 13 and accompanying figures.

In all embodiments of the invention, carbon loading can vary but is preferably 1 to 10%, more preferably about 5%. The carbon used is preferably nano-sized acetylene carbon black powder.

The first transition metal suboxide and the second transition metal suboxide can each be selected from the group consisting of tungsten suboxide, cobalt suboxide, Co₃O₄, Na_1.0Mo_1.5WO_6.0, Na_0.9Mo₆O₁₇, Na_1.0Ti_1.5WO_4.5, Na_1.2Ti_0.34WO₄, Ti₄O₇, Ti₅O₉, K_1.28 Ti₈O₁₆, K_1.04Ti₈O₁₆, K_0.48 Ti₈O₁₆, Na₄WO₃, Na_0.90WO_1.81, Na_0.82WO_1.81, Na_0.74WO_1.81, K_0.9WO₃, WO_2.72, WO_2.82, WO_2.9, Na₂WO₄, Na_8.2WO, Na₂O₂WO₃, Na_1.2Ti_0.34WO₄, Na_1.2Cu_0.31WO_7.2, Na_1.2Mo_0.31WO_5.2, and Na₂O₄WO₃.

In another aspect, the anode mixture, the SSE mixture, and the cathode mixture are ground in a high-shear, high intensity blender for at least one minute.

In a further aspect, the first layer, second layer and the third layer are not separated by physical separators. The first transition metal suboxide and third transition metal suboxide can each selected from the group consisting of titanium, cobalt, tungsten, or cesium. The first transition metal suboxide can comprise titanium suboxide. In another aspect, each of the anode mixture and the SSE mixture has a water content of less than about 25 weight percent.

The second transition metal suboxide can comprise cobalt suboxide. In a further aspect, each of the first layer, the second layer and the third layer has a water content of less than about 5 weight percent.

Each of the first layer, second layer and the third layer can comprise a solid-state electrolyte comprising tungsten suboxide and cerium dioxide. In a further aspect, each of the anode mixture, the SSE mixture, and the cathode mixture has a water content of less than about 10 weight percent.

The binder can be selected from the group consisting of, unsintered polytetrafluoroethylene (PTFE), FEP, Paraffin and epoxy. In one aspect, the binder is less than about 50 volume percent of each of the first layer, second layer and the third layer.

In yet another aspect, the first layer, the second layer, and the third layer are formed by compression in a roller mill to produce a back-extrusion. In this aspect, the solid-state energy harvester can optionally not contain physical separators between the first layer and the second layer and the third layer.

In one aspect, the anode mixture comprises about 17% (w/w) CeO₂, 33% (w/w) WO_2.9, 50% (w/w) Ti₄O₇ and 40 volume percent powdered PTFE.

The cathode mixture can comprise about 17% (w/w) CeO₂, 33% (w/w) WO_2.9, 50% (w/w) Co₃O₄ and 40 volume percent powdered PTFE.

In one aspect, the anode mixture comprises about 17% (w/w) CeO₂, 33% (w/w) WO_2.9, 50% (w/w) Ti₄O₇ and 40 volume percent powdered PTFE; the solid-state electrolyte mixture comprises about 67% (w/w) WO_2.9, 33% (w/w) CeO₂ and 40 volume percent powdered PTFE and the cathode mixture comprises about 17% (w/w) CeO₂, 33% (w/w) WO_2.9, 50% (w/w) Co₃O₄ and 40 volume percent powdered PTFE.

In another aspect, each of the first layer, second layer and the third layer comprise Teflon particles, the binder comprise powders, and each of the first layer and the second layer is made using a roller mill to force extrude the powders through rollers of a mill, and extrude the Teflon particles into fibrils.

The solid-state energy harvester can optionally be encased in a non-conductive, essentially gas impervious housing. The non-conductive, essentially gas impervious housing can have a gas inlet and a gas outlet on opposite sides of the non-conductive, essentially gas impervious housing.

In a further aspect, the non-conductive, essentially gas impervious housing is made of a polyacrylate or a polycarbonate.

Transition Metal Suboxide and Defect Theory

The general theory described herein applies to the exemplary active components in the energy harvester, e.g., Ti₄O₇, WO_2.9, Co₃O₄ and CeO₂. Members of non-stoichiometric metal oxide suboxides called the Magnéli phases exhibit lower bandgaps and resistivities, with the highest electrical conductivities. These phases have high oxygen vacancies and electronic connections increase with increases in oxygen vacancies. Electrons from the d-orbital split into two components with different energies called the t2g and eg orbitals. The electron-conducting path can be switched back and forth by the drift of charged oxygen vacancies. The conductivity in the conduction band can result either from these oxygen vacancies and/or metal induced defects. It has been suggested that the hypo-stoichiometry can result from either oxygen vacancy or metal interstitial, as expressed in the Kroger-Vink notation by the following two Redox reactions, respectively:

$O_O^X\to V_O^{\mathrm{••}}+2e^{\prime }+\frac{1}{2}{O}_{2\left(g\right)}\mathrm{and}{M}_M^X+O_O^X\to M_i^{\mathrm{••}}+2e^{\prime }+\frac{1}{2}{O}_{2\left(g\right)}$

See, e.g. Zhang et al. “The role of single oxygen or metal induced defect and correlated multiple defects in the formation of conducting filaments”, Department of Precision Instrument, Centre for Brain Inspired Computing Research, Tsinghua University, Beijing, China, incorporated herewith in its entirety.

These equations allow charge movement reactions to be described separately, for example as:

$O_o^x+h·\to O{·}_0$

Where O^x_o, denotes an oxygen ion sitting on an oxygen lattice site, with neutral charge, h denotes an electron hole, and O₀ denotes a singlet oxygen atom with a single charge. Also,

${\mathrm{Ce}}_{\mathrm{ce}}^x+e^{-}\to {\mathrm{Ce}}_{{\mathrm{ce}}^{\prime }}^{\prime }$

Where Ce^x_ce denotes a cerium ion sitting on a cerium lattice site, with neutral charge, and Ce′_ce′ denotes a cerium anion on an interstitial site, with single negative charge.

This is an exemplary description of how a cerium ion sitting on a cerium lattice site with neutral charge can accept an electron and become a charged cerium ion on that lattice site, and how charge is transferred in the solid state electrolyte described herein.

See, also, “Solid state aspects of oxidation catalysis” by Gellings et al., Laboratory for Inorganic Materials Science, University of Twente, PO Box 217, NL-7500 AE Enschede, The Netherlands, (2000), incorporated herewith in its entirety.

For protonic defects in oxides, an illustrative formation reaction between water molecules and oxygen vacancies is as follows:

$O_O^X+V_O^{\mathrm{••}}+H_{2}O\left(g\right)\to 2{\mathrm{OH}}_O^{•}$

In this reaction, two effectively positive hydroxyl-groups on regular oxygen positions are formed. Additional defect reactions where protonic defects are formed by reaction with hydrogen are set forth below. A reaction with electron holes is as follows:

$2h^{•}+2O_O^X+H_2\to 2{\mathrm{OH}}_O^{•}$

where the presence of excess holes is required. Alternatively, oxidation of hydrogen under formation of free electrons is illustrated by the following reaction:

$2O_O^X+H_2\to 2{\mathrm{OH}}_O^{•}+2e^{\prime }$

where the electrons are assumed to be donated to the conduction band.

Gellings, et. al., propose that at low temperatures, the dissolution of water in the Li/MgO catalyst occurs through reaction with oxygen, or with oxygen vacancies, as shown in the following equations:

$V_O^{\mathrm{••}}+O_O^X+H_{2}O\to 2{\mathrm{OH}}_O^{•}\mathrm{and}2O_O^X+H_{2}O\to V_{\mathrm{Mg}}^{″}+2{\mathrm{OH}}_O^{•}$

At low temperatures (e.g., 673 K) the conductivity is found to be caused by OH_o ions as the main charge carriers. This shows the importance of water in the transport of charge in both the Ti₄O₇ anode and the CeO₂ solid-state “electrolyte”.

It has been theorized that CeO₂ can store and transport oxygen and, in its reduced state, CeO₂ splits water to release hydrogen as shown in the following equations (see Analytical Model of CeO₂ Oxidation and Reduction by B. Bulfin, et al., School of Physics, Trinity College Dublin, College Green, Dublin 2, Ireland, J. Phys. Chem. C, 2013, 117 (46), pp 24129-24137, DOI: 10.1021/jp406578z, Publication Date (Web): Oct. 16, 2013, incorporated herewith in its entirety).

${\mathrm{CeO}}_2\to {\mathrm{CeO}}_{2-\delta }+\frac{\delta }{2}{O}_2$ $\mathrm{and}$ ${\mathrm{CeO}}_{2-\delta }+\delta H_{2}O\to {\mathrm{CeO}}_2+\delta H_2$

Bulfin et al. explain the relationship between cerium dioxide and its suboxide states, and the resulting activity of these molecules, mostly pertaining to manufacturing synfuels and catalytic converters. The relationship described by Bulfin et al. uses the Arrhenius equation, which teaches that the rate constant of most chemical reactions increases by the negative power of the reciprocal absolute temperature. According to Bulfin et al. the effect is shown at above 500° C. However, many of the graphs in Bulfin et al. show that some activity occurs at ambient temperatures.

In one aspect, the solid-state energy harvesters described herein perform well up to about 90 degrees centigrade in the presence of a relative humidity of at least about 85%.

In one aspect, the energy harvesters described herein have five components: WO_2.9, CeO₂, Co₃O₄, Ti₄O₇ and unsintered PTFE powder. Table 1 below shows the composition of an exemplary aspect, wherein percentages are weight-percent, except for PTFE binder given in volume percent. The components 1 and 2 in Table 1 are components of the Solid State Electrolyte (SSE), component 3 is the active ingredient of the anode, and component 4 is the active component of the cathode. PTFE is the binder. The three electrodes shown in Table 1 include the titanium-containing anode, the separator, and the cobalt-containing cathode. Moisture values were measured and percentages were determined from the results of several factorial experiments shown below in Table 1. The “separator” layer can be omitted from the design resulting in a two-electrode design.

TABLE 1
Components	Percentages (w/w) unless indicated otherwise
	Max		Separator
	Moisture	Anode	(If Present)	Cathode
CeO2	SSEa	4.8%	17%	33%	17%
WO2.9	SSEb	9.1%	33%	67%	33%
Ti4O7	Anode	20.3%	50%
Co3O4	Cathode	0.72%			50%
T7c	Binder	0.50%	40 Vol %	40 Vol %	40 Vol %

In one aspect, cerium dioxide (CeO₂) and a tungsten suboxide are used as solid-state electrolytes. In this aspect, the tungsten suboxide is WO_2.9. In this aspect, the components are present in a ratio of 1 part CeO₂ to 2 parts WO_2.9.

Cerium dioxide is a large molecule (MW=172.12) with the oxygen atoms on the outer portion of the crystal structure. The oxygen atoms are loosely attached and therefore easily moved from one molecule to the next. In FIG. 1, cerium atoms 101, and oxygen atoms 102 are shown. Without being bound by theory, it is believed that the atomic size difference between cerium atoms 101 and oxygen atoms 102 allows the oxygen atoms relative freedom to move around and catalyze redox reactions. FIG. 1 illustrates how loosely connected the exemplary oxygen atoms are from the large lanthanide cerium.

In another aspect, the energy harvester contains a low percentage of water. Neutral water has a 1×10⁻⁷ molarity of H⁺ and OH⁻ ions used in the above equations, and illustrated by the following:

$H_{2}O\to H^{+}+{\mathrm{OH}}^{-}$ $2H_{2}O\to 2H_2+O_2$

The CeO₂ as described in Zhang can catalyze this reaction. While not wishing to be bound by theory, the following 2 mechanisms may be relevant.

Mechanism 1

The use of CeO₂ as a catalyst with mobile oxygen atoms is described in an article dealing with catalytic converters in trucks, “Structural, redox and catalytic chemistry of ceria based materials”, by G. Ranga Rao et al., Bulletin of the Catalysis Society of India (2003) 122-134 incorporated herewith in its entirety. The CeO₂ as a catalyst was used to catalyze conversion of methane gas to CO₂ and water among other pollutant cleaning catalysis.

The following equations (as illustrated in FIG. 2 where 201=Ce4+, 202=O2−, 203=Vacancies and 204=Ce3+) show the steps of the process, where V=Vacancy:

$\begin{array}{cc}{H}_2+{\mathrm{Ce}}_4^{+4}{O}_4^{-2}<-\mathrm{Step}1->& \mathrm{Equation}3\end{array}$ $\begin{array}{cc}{\mathrm{Ce}}_4^{+4}{O}_4^{-2}{H}_2<-\mathrm{Step}2->& \mathrm{Equation}4\end{array}$ $\begin{array}{cc}{\mathrm{Ce}}_2^{+4}{\mathrm{Ce}}_2^{+3}{O}_3^{-2}{H}^{+}V+{\mathrm{OH}}^{-}<-\mathrm{Step}3->& \mathrm{Equation}5\end{array}$ $\begin{array}{cc}{\mathrm{Ce}}_2^{+4}{\mathrm{Ce}}_2^{+3}{O}_3^{-2}V+H_{2}O<-\mathrm{Step}4->& \mathrm{Equation}6\end{array}$ $\begin{array}{cc}{\mathrm{Ce}}_2^{+4}{\mathrm{Ce}}_2^{+3}{O}_3^{-2}V& \mathrm{Equation}7\end{array}$

Sum equation:

$\begin{array}{cc}{H}_2+{\mathrm{Ce}}_4^{+4}{O}_4^{-2}\to {\mathrm{Ce}}_2^{+4}{\mathrm{Ce}}_2^{+3}{O}_3^{-2}V& \mathrm{Equation}8\end{array}$

Mechanism 2

Cerium dioxide (CeO₂) is well known for its oxygen mobility. CeO₂ undergoes rapid redox cycles, for example:

$\begin{array}{cc}2{\mathrm{CeO}}_2\to {\mathrm{Ce}}_2{O}_3+1/2O_2& \mathrm{Equation}9\end{array}$ ${\mathrm{Ce}}^{+4}\to {\mathrm{Ce}}^{+3}\mathrm{Eo}=1.61$

Cerium dioxide acts as an oxygen buffer by storing/releasing O₂ due to the redox couple Ce⁺⁴/Ce⁺³. This is a reversible reaction, making it an oxygen storage material. The reaction moves in the opposite direction in oxygen-free conditions (e.g., under Argon). This facilitates the other electrode reactions with Ti₄O₇ and Co₃O₄ as discussed below.

Without wishing to be bound by theory, the actual mechanism may well be some combination of the two pathways discussed above, combined with the “defect theory” described above.

Point of Zero Charge

In one aspect, the chosen suboxide used in the anode and cathode has well separated (e.g., greater than 1, between 1 and 4, 1.5) Point of Zero Charge (PZC). PZC refers to the pH established within the adsorbed water as it dissociates. Without being bound by theory, it is believed that this imbalance drives the potential difference in the electrodes. See, e.g., Parks et. al., “The Zero Point of Charge of Oxides,” MIT, 1961; “Surface charge characterization of metal oxides by potentiometric acid-base titration, revisited theory and experiment” by Marta Szekeres, Etelka Tombácz, Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. 1, 6720 Szeged, Hungary 2012.

Dissolved Oxygen and Water Interaction

In another aspect, the energy harvester preferably contains small amounts of water in the electrodes, which elicit a response to the presence of oxygen—or conversely, to the removal of oxygen by flooding with argon (0% oxygen). Oxygen does not ionize when dissolved in water, but is held between the water molecules as shown in FIG. 3 where the rectangles 301 highlights the water molecule (oxygen is 102 and hydrogen is 302), and do not represent entities in and of themselves. Oxygen molecule (303) becomes intimately connected to the holding of oxygen diatomic molecules, and therefore, the transport of those molecules from place-to-place. In a conventional energy harvester, this could be considered an “electrolyte” but in the present energy harvester, the electrodes may be separated by nickel-expanded metal, so the transport of charge is within an electrode, not between electrodes. Combined with the understanding in the above paragraphs dealing with the defects in the suboxide crystal structure, one aspect of the charge transport is free flow of charge with relatively small amounts of water.

In certain aspects, the anode may contain between 0.01% and 15% water. In other aspects the anode may contain between 0.1% and 10%, 1% and 8%, or 2% and 5% water. In certain aspects, the second layer may contain between 0.01% and 8% water. In other aspects, the second layer may contain between 0.1% and 5%, 1% and 4%, or 2% and 3% water. In certain aspects, the cathode may contain between 0.01% and 5% water. In other aspects, the cathode may contain between 0.1% and 10%, 1% and 8%, or 2% and 5% water.

In one aspect, a WO_2.9 and CeO₂ separator sits between the anode and cathode, to permit transfer of the charge, possibly on oxygen atoms. This intermediate layer contains cerium dioxide mixed with tungsten suboxide (WO_2.9), and in one example, in even weights. Tungsten has many oxidation states, but +6 and +4 is the most stable. WO_2.9 gives the tungsten a valence of +5.8, which is an average over the crystal. WO_2.9 is available from Global Tungsten (gobaltungsten.com).

FIG. 4 shows the crystal structure of WO_2.9 and the effect of dehydration on charge transport. The octahedrons shown in 401 are the tungsten orbital fields, the larger black dots 301 represent water molecules, the small black dots 102 represent the singlet oxygen's in the crystals, and the small pale dots 302 represents hydrogen atoms. Without wishing to be bound by theory, it is believed that the water molecules shown in FIG. 4 allow for more movement of the WO₃ crystal components. The same structure is present in the case of WO_x (also indicated as WO_3-x), but some of the charge carrying oxygens are missing from the mass of crystals. FIG. 4 illustrates the effect on the crystal structure as the crystal dehydrates from “a” with sufficient water molecules 301 to the mildly dehydrated “b” and finally the fully dehydrated “c”. In one aspect, the energy harvester is made in the dehydrated “c” state, and then allowed to hydrate spontaneously through “b” to “a” in situ.

The following reaction scheme is illustrative:

Reduction (“V”=“Vacancy”)

$\begin{array}{cc}2\left(W^{+6}-O-W^{+6}\right)+4e^{-}+O_2-->& \mathrm{Equation}10\end{array}$ $\begin{array}{cc}2\left(W^{+5}-V-W^{+5}\right)2\left(O\right)+4e^{-}-->& \mathrm{Equation}11\end{array}$ $\begin{array}{cc}2\left(W^{+5}-O-W^{+5}\right)+4e^{-}\mathrm{SUM}:2\left(W^{+6}-O-W^{+6}\right)+O_2-->2\left(W^{+5}-O-W^{+5}\right)+2e^{-}& \mathrm{Equation}12\end{array}$

Oxidation

$\begin{array}{cc}2\left(W^{+5}-O-W^{+5}\right)+O_2\to & \mathrm{Equation}13\end{array}$ $\begin{array}{cc}2\left(W^{+6}-O-W^{+6}\right)+\left(O\right)+2e^{-}\to & \mathrm{Equation}14\end{array}$ $\begin{array}{cc}2W^{+5}+O_2\to & \mathrm{Equation}15\end{array}$ $\begin{array}{cc}\left(W^{+6}-O-W^{+6}\right)+\left(O\right)+2e^{-}& \mathrm{Equation}16\end{array}$ $W^{+6}\to W^{+4}\left(W^{+6}\to W^{+5}\mathrm{unknown}\right)E_o^{~}+/-0.91\mathrm{volts}$

E_o source: http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/electrode.html

$\begin{array}{cc}\mathrm{SUM}:2\left(W^{+5}-O-W^{+5}\right)+O_2\to 2\left(W^{+6}-O-W^{+6}\right)+2\left(O\right)+2e^{-}& \mathrm{Equation}17\end{array}$

Summation of the separator reactions

$\begin{array}{cc}2\left(W^{+6}-O-W^{+6}\right)+O_2\stackrel{H2O}{⟷}2\left(W^{+5}-O-W^{+5}\right)+2e^{-}& \mathrm{Equation}18\end{array}$ $\mathrm{and}$ $\begin{array}{cc}2\left(W^{+5}-O-W^{+5}\right)+O_2\stackrel{H2O}{⟷}2\left(W^{+6}-O-W^{+6}\right)+2\left(O\right)+2e^{-}& \mathrm{Equation}19\end{array}$ $\mathrm{and}$ $\begin{array}{cc}2{\mathrm{Ce}}_2{O}_3+2O^{-2}\stackrel{H2O}{⟷}4{\mathrm{CeO}}_2+4e^{-}& \mathrm{Equation}20\end{array}$

In one aspect, oxygen enters the separator, and both singlet oxygen and electrons leave to move into the anode. In this aspect, the singlet oxygens react with the cerium oxide to transfer more electrons. Water can have a catalytic role in these events.

In one aspect, the active component of the cathode is cobalt (II, III) suboxide (Co₃O₄). FIG. 5 shows the crystal structure of Co₃O₄ where the Co⁺² is shown as spheres #2 (501), Co⁺³ spheres #3 (502), and the oxygen atoms are light colored spheres #1 (202). Cobalt has two oxidation states, +2 and +3, both of which are present in this crystal. The oxygen atoms are loosely bound to the large cobalt atom and electronegative compared to a Ti₄O₇ anode. The admixing of CeO₂ with Co₃O₄ allows the dispersion of charge carrying oxygen atoms, reducing the valence of the cobalt from +2 & +3 in Co₃O₄ to only valence +2 in CoO, releasing an oxygen atom to the pool of oxygens associated with the CeO₂.

The above reaction results in CeO₂—Co₃O₄ crystallite reversible redox freeing or absorbing oxygen depending on the direction of oxygen concentration, as shown by the following root equations:

$\begin{array}{cc}{O}_2+4e^{-}\to 2O^{-2}& \mathrm{Equation}19\end{array}$ $\begin{array}{cc}2{\mathrm{Co}}_3{O}_4\to 6\mathrm{CoO}+O_2& \mathrm{Equation}20\end{array}$

Summing these two equations (cation reduced in cathode via Co^+2.67↔Co⁺²):

$\begin{array}{cc}2{\mathrm{Co}}_3{O}_4+4e^{-}\to 6\mathrm{CoO}+O^{-2}& \mathrm{Equation}21\end{array}$

Equation 9 from above:

$\begin{array}{cc}2{\mathrm{CeO}}_2-->{\mathrm{Ce}}_2{O}_3+1/2O_2& \mathrm{Equation}9\end{array}$

Summing Equations 21 and 9 gives:

$\begin{array}{cc}{\mathrm{Co}}_3{O}_4+4e^{-}+2{\mathrm{CeO}}_2-->3\mathrm{CoO}+O^{-2}+{\mathrm{Ce}}_2{O}_3+1/2O_2& \mathrm{Equation}22\end{array}$

Looking only at the cations:

${\mathrm{Co}}^{+2.67}+{\mathrm{Ce}}^{+4}-->{\mathrm{Co}}^{+2}+{\mathrm{Ce}}^{+3}+1.76e^{-}{E}_o~1.715$

The above description is an example of how oxygen atoms freely flow from one cation to the other carrying the charge in aspects described herein.

In one aspect, the active component of the anode is Ti₄O₇ (also expressed as Ti_nO_2n-1) wherein n is between 4 and 10. Ti_nO_2n-1 is a member of non-stoichiometric titanium oxides called the Magnéli phases, which exhibit lower bandgaps and resistivities, and which have the highest electrical conductivities reported for Ti₄O₇. The atomic structure of this molecule appears in FIG. 6, where the titanium atoms are shown as “Ti1”-“Ti4” for each titanium atom (601-604) in each Ti₄O₇ molecule and oxygen shown as “O” atoms (102). With Ti₄O₇, titanium has a valence state of +3.5, which is an average value of the crystal, since valence states must be an integer. As electrons flow in through the separator, the Ti₄O₇ molecule passes them through to the anode conduction band located in the Magnéli phase, then into the anode current collector electrode.

The equations can be summarized as follows:

$\begin{array}{cc}{H}_{2}O-->H^{+}+{\mathrm{OH}}^{-}& \mathrm{Equation}23\end{array}$ $\begin{array}{cc}4{\mathrm{Ti}}_2{O}_3+2{\mathrm{OH}}^{-}+2O^{-2}-->2{\mathrm{Ti}}_4{O}_7+H_{2}O+2e^{-}& \mathrm{Equation}24\end{array}$

Equation 9 from above (expressed in anodic form):

$\begin{array}{cc}{\mathrm{Ce}}_2{O}_3+1/2O_2-->2{\mathrm{CeO}}_2& \mathrm{Equation}9\end{array}$

Summing Equations 12 and 9 gives:

$\begin{array}{cc}4{\mathrm{Ti}}_2{O}_3+2{\mathrm{OH}}^{-}+O^{-2}+2{\mathrm{Ce}}_2{O}_3+O_2-->2{\mathrm{Ti}}_4{O}_7+H_{2}O+4{\mathrm{CeO}}_2+2e^{-}& \mathrm{Equation}24\end{array}$

Looking only at the cations:

${\mathrm{Ti}}^{+3}+{\mathrm{Ce}}^{+4}-->{\mathrm{Ti}}^{+3.5}+{\mathrm{Ce}}^{+3}{E}_o~1.085$

Full Energy harvester Flow:

$\mathrm{Cathode}:{\mathrm{Co}}_3{O}_4+2e^{-}+4{\mathrm{CeO}}_2-->4\mathrm{CoO}+2{\mathrm{Ce}}_2{O}_3+O_2+1/2O_2\mathrm{Anode}:4{\mathrm{Ti}}_2{O}_3+2{\mathrm{OH}}^{-}+O^{-2}+2{\mathrm{Ce}}_2{O}_3+O_2-->2{\mathrm{Ti}}_4{O}_7+H_{2}O+4{\mathrm{CeO}}_2+2e^{-}\mathrm{Overall}:{\mathrm{Co}}_3{O}_4+4{\mathrm{CeO}}_2+4{\mathrm{Ti}}_2{O}_3+2{\mathrm{OH}}^{-}+2H^{+}+1/2O_2+2{\mathrm{Ce}}_2{O}_3-->3\mathrm{CoO}+2{\mathrm{Ce}}_2{O}_3+2{\mathrm{Ti}}_4{O}_7+2H_{2}O+4{\mathrm{CeO}}_2$

Thus, oxygen and water (which dissociates) enter the cathode and the final acceptor of the oxygen is a hydroxyl ion producing water vapor.

Table 2 below shows relevant potentials, which are similar to the potentials observed in OCV experiments such as FIG. 10 shows.

TABLE 2
Using standard potential
A	Ce+4 --> Ce+3	1.61	V
B	Ti+3 --> Ti+4	0.56	V	Oxidized
C	Co+3 --> Co+2	1.82	V	Reduced
D	W+6 --> W+4	0.21	V	W + 6 --> W + 5 unknown
Assuming that the admixture gives the average of the potentials
Anode:	B + A=	1.085	V	Ti+3 + Ce+4 --> Ti+3.5 + Ce+3
Separator:	D + A=	0.91	V	W+6 --> W+4 (W+6 --> W+5 unknown)
Cathode:	C + A=	1.715	V	Co+2.67 + Ce+4 --> Co+2 + Ce+3
Energy	Cathode − Anode=	0.63	V
harvester:

Sources of Materials Used:

• • Ti₄O₇, Ti-Dynamics Co. Ltd, Magnéli Phase Titanium Suboxides—N82, www.Ti-dynamics.com.
  • Nano WO_2.9, “Tungsten Blue Oxide” http://globaltungsten.com #P005016
  • Co₃O₄ Cobalt (II, III) oxide, www.fishersci.com #AAA1612130
  • CeO₂ Cerium (IV) oxide, www.fishersci.com #AC199125000
  • Teflon 30 dispersion “DISP 30”, www.fishersci.com #501090482 or www.chemours.com
  • PTFE 7CX: www.chemours.com
  • DAIKIN F104 unsintered Teflon powder
  • CABOT Vulcan XC72R (GP-3875) carbon V72
  • ASBURY Graphite Mills “Nano 307”
  • Cross-Bonded expanded metal 4Ni 5-060 P&L x 4: Dexmet Corporation, 22 Barnes Industrial Rd S, Wallingford, CT 06492 (www.dexmet.com)
  • Nickel 10 mil Shim Stock, (www.mcmaster.com) #9707K79
  • ¾″ Silver bezel: (www.riogrande.com) #950272
  • 24kt Gold Cyanide Plating Solution: (www.riogrande.com) #335082
  • 24kt Gold sheet for anode: (www.riogrande.com) #608030
  • Rolling Mill made by Durston (www.durston.co.uk, #DRM F130R)

Example 1: Pellet Electrode

A pellet electrode is made as follows.

Weigh powders: anode is 17% CeO₂, 33% WO_x, 50% Ti₄O₇; solid-state separator is 33.3% CeO₂ and 66.7% WO_x; cathode is 17% CeO₂, 33% WO_x and 50% Co₃O₄; binder is 40% by volume Teflon 7c.

Admix the powders in a high-intensity blender. Prepare a ¾″ compassion cylinder, and lubricate it with a small amount of Polymist F-5AEx by Ausimont sintered Teflon powder. Place a ¾″ cross-bonded expanded metal disk (Dexmet Corp, 4Ni 5-00 P&L x 4) in the bottom of the compression cylinder. Pour the blended powders into the cylinder. Add another ¾″ cross-bonded expanded metal disk on top of the powders. Place a stainless steel cover plate over the cylinder. Compress to 5000 Pounds (11,318 psi) and hold for a few seconds. Remove from the cylinder, and measure and record the weight and thickness.

Knowing the density of all the components, the weight and volume is used to calculate the porosity of the resulting pellet. A pressure is chosen that provides good binding of the powders and good porosity. In this example, 5000 pounds was found to be an exemplary pressure.

The pellets are then placed in a humidity chamber, which is at 100% relative humidity for four days, bringing the internal water content to about 5% in the anode, about 3.5% in the separator, and about 0.6% in the cathode.

FIG. 7A shows the physical layout of an exemplary resulting energy harvester with three electrodes: Anode pellet (7A1), Separator pellet (7A2), Cathode pellet (7A3), and nickel cross-bonded expanded metal (7A6) between each layer with the anode nestled within a gold bezel (7A4) held in with epoxy adhesive (7A5). Each pellet also has nickel expanded metal on each surface (7A6).

The Separator pellet (7A2) is often omitted from the design resulting in a two-electrode design.

Example 2A: Rolled Electrode

An embodiment of a rolled electrode is made as follows:

Weigh powders: anode is 17% CeO₂, 33% WO_x, 50% Ti₄O₇; solid-state separator is 33.3% CeO₂ and 66.7% WO_x; cathode is 17% CeO₂, 33% WO_x and 50% Co₃O₄; binder is 40% by volume Teflon 7c. Admix in a high-intensity blender.

Adjust the gap of a 60 mm diameter precision rolling mill made by Durston (www.durston.co.uk, #DRM F130R) to 0.178 mm (0.007″). Rolls must be parallel to a high degree. With the rollers situated in a horizontal position, pour the powder onto the roller nip. Slowly rotate the rollers toward the nip, drawing the powder into the nip and producing a freestanding sheet on the underside of the rollers. Remove the sheet and lay it on a clean sheet of paper. Cut a disk of each sheet using an arch punch, e.g., a ¾″ (19 mm) diameter punch #3427A19 from McMaster Carr. In one aspect, the cathode is 1″ diameter, the separator is ⅞″ diameter and the anode is ¾″ diameter to insure no cross electrode shorting. In more refined production situations, the diameters can be the same.

Lay the cathode sheet onto a current collector (e.g., gold or gold-plated nickel or other metal). An intra-electrode current collector may or may not be used over this first sheet. A 10-mil nickel shim stock, flattened nickel expanded metal, or no spacer (sheets in direct contact) may be used if an intra-electrode current collector is used. Place the separator sheet next, then the anode sheet, following the protocol used for the current collector. Place a current collector over the anode.

The resulting energy harvester is assembled into the testing apparatus, e.g., using 40-psi force compression.

FIG. 7B shows the physical layout of a three electrode, thin rolled energy harvester. This example uses no metallic spacers. In FIG. 7B, there is an anode layer 7A1, an anode layer 7A1, a separator layer 7A2 and a cathode layer 7A3 sandwiched between an anode current collector 7B1 and a cathode current collector 7B2. None of these example energy harvesters contain an insulating separator as most liquid electrolyte energy harvesters do.

The Separator layer (7A2) is often omitted from the design resulting in a two-electrode design.

Example 2B: Rolled Electrode

To resolve sticking problems with the rollers described above, another embodiment of a rolled electrode was made as follows:

Weigh powders: anode is 17% CeO₂, 33% WO_x, 50% Ti₄O₇; solid-state separator is 33.3% CeO₂ and 66.7% WO_x; cathode is 17% CeO2, 33% WO_x and 50% Co₃O₄; binder is 40% by volume Teflon 7c. Admix in a high-intensity blender.

Use a 60 mm diameter precision rolling mill made by Durston (www.durston.co.uk, #DRM F130R) (801 of FIG. 8) situated in a vertical position (801). Cut two pieces of 1/16″ (1.58 mm) sintered Teflon sheeting (McMaster Carr #8545K13) or thicker about 100 mm wide (about 4 inches) and about 150 mm long (about 6 inches) (802). Adjust the roller mill gap to be 2 times the thickness of the Teflon sheet plus 0.007″ (0.178 mm). Alternatively, the rollers can be pressed together pneumatically rather than under a constant gap. This way, the thickness of the powder going into the mill can vary more than if using a constant gap. A pair of 4-inch pancake cylinders (Mead Fluid Dynamics SS-400X1.125-FB), under 50-psi giving 1257 pounds force can be used. About 25 psi (630 Pounds Force) can be used to produce a strong sheet, while maintaining porosity in a useful range(e.g., 0% to about 50% porosity).

Pour the well-blended powder on one sheet (803), doctoring between stainless steel rods to a constant thickness and width, and place the second sheet over it. Slowly rotate the rollers toward the nip, drawing the Teflon sheets and powder into the nip and producing a freestanding sheet between the Teflon sheets. The Teflon sheets (802) may be replaced with Teflon coated metal sheets of the same size cut from a cookie sheet, for example. Remove the electrode sheet (804) using a safety razor or other sharp instrument and lay it on a clean sheet of paper. Cut a disk of each sheet using an arch punch, e.g., a ¾″ (19 mm) diameter punch (e.g., #3427A19 from McMaster Carr). Lay the cathode sheet onto a current collector (e.g., gold plated brass or nickel). A current collector can optionally be used over this first sheet. A 10-mil nickel shim stock, flattened nickel expanded metal, or no spacer (sheets in direct contact) may be used. Place the separator sheet next, then the anode sheet, following the protocol used for the current collector. Place a current collector over the anode; here, gold plated nickel or brass shim stock was used. The resulting energy harvester is assembled into the testing apparatus, e.g., using 40-psi force compression.

In another aspect, the cathode is 1″ diameter, the separator is ⅞″ diameter and the anode is ¾″ diam. In this aspect, cross electrode shorting is reduced or eliminated. In another aspect, the diameters can be the same.

The separator layer can be omitted with the anode and cathode simply placed in immediate contact with each other. In another aspect, the anode and cathode have a concentration gradient of materials to produce, for example, higher impedance near the interface between the electrodes.

In some aspects having carbon (graphite or carbon black) added to the anode and the cathode electrodes, no additives are added to the SSE layer situated between the anode and cathode. The separation of charge in this aspect is accomplished by using the higher impedance of the SSE layer. In a further aspect, no load can be lower than the total output impedance of the finished unit.

In many energy harvester builds, the cell is placed within a plastic enclosure. Exemplary plastic enclosures have been made from polyacrylate and polycarbonate, but could be composed of any non-conductive plastic material. The adhesive used has been “airplane glue” when using polycarbonate or methyl ethyl ketone (MEK) when using polyacrylate. In one aspect, the functioning cell is enclosed in a space with a gas inlet and outlet for increased control of the gaseous reactants, and to make the resulting cell more robust. When using an enclosure, the gases are pumped across the electrodes at a rate from 5 to 300 ml/minute depending on the test involved with an exemplary rate of 50 ml/minute per cell.

Example 3: Testing

The test apparatus holds the energy harvester under 125 pounds force onto anode and cathode current collectors, which are gold-plated, nickel 200 or brass resting on cast acrylic supports. Testing was done using a Solartron S1287 Electrochemical Interface and a Solartron S1250 Frequency Response Analyzer, but many other test apparatuses would work as well. The pellets were tested as individuals and as an energy harvester between gold electrodes. The entire apparatus was situated inside a plastic bag for gas environment experiments. Typically, tests can be conducted in air (20% O2), 100% O2 and Argon (0% oxygen). When testing the assembled energy harvester, the cathode is used as the Working Electrode and the Working Reference. The anode is the Counter Electrode and the Reference Electrode. One would expect negative currents when shorting or potentiostatic discharges of the energy harvester in this example

When the Energy Harvesting cell is built into an air-tight enclosure, then gasses are passed into the cell via a port at one end of the enclosure with the gasses escaping from an exhaust portal. Typically, tests were conducted in air (20% O2), 100% O2 and Argon (0% oxygen).

Tests include the set below:

• • Open Circuit Voltage (OCV) for 1 minute
  • AC Impedance Spectroscopy from 1 MHz to 1 mHz with 10 data per decade.
  • The units are normalized for physical conditions by measuring the thickness of the compressed electrode or the pellet thickness and knowing the surface area.
  • Polarization curve from OCV+0.25 to zero volts at 1 mv per second scan rate.
  • This gives us the Exchange Potential (E_o), Limiting current density and power density.
  • Cycling Voltammogram from OCV to +1.0 volt, to −1.0 volt, cycling five times at 50 mV/sec. The data resulting from this included:
  • R_functional, is calculated by taking the Maximum current at +1 volt and the minimum current at −1.0 volts and calculating the slope between those two points as a resistance by using Ohms law (R_functional=dV/di).
  • Hysteresis at 0 volts: If the electrons are consumed and released during the cycle as they are with an electrochemical system or a capacitive system, then there is a spread in the current when the direction of potential is rising as compared to falling. In essence, the electrons are being consumed or release as opposed to simply passing through the system (as they are through a resistor). The greater this hysteresis is, the better the crystals are for storage or release of energy. The current density spread at positive and negative directions is the hysteresis which can be measured as the voltage at zero current.

Example 4

CeO₂ is used in equal parts in all three electrodes: the Ti₄O₇ Anode, the WO_2.9 separator, and the Co₃O₄ cathode. CeO₂ is admixed with 10% Teflon 7c by DuPont. Each pellet contains 2 grams of the active material and a pure nickel expanded metal (from Dexmet) on both surfaces. The pellets are made as described above and held in 100% relative humidity for four days giving moisture content of 3.7% for the anode, 1.6% for the separator, and 0.5% for the cathode pellet. To assemble the energy harvester, the anode pellet is adhered with 5-minute epoxy resin at its perimeter to a heavily gold-plated silver bezel while held under 40 PSI compression to ensure good contact with the gold. The separator is sealed around its perimeter with epoxy resin; this ensures that all oxygen must be transported from the Cathode through the separator.

This pellet design energy harvester as described in FIG. 7A above was then dead shorted for an hour and allowed to recover for an hour over eight cycles all while in an oxygen environment. The chamber was not hermetically sealed, so oxygen diffuses out and nitrogen diffuses in, but at very low rates. FIG. 9 shows the current density during the shorting for the many discharges. It should be noted that all discharge tests have a reversed vertical axis because the cathode is considered to be the working electrode, so currents are negative and open circuit voltages will be positive. During the highest two lines (A), oxygen was introduced at about 700 seconds and the other at about 1600 seconds, oxygen is re-introduced and the jump in performance is noted. All other lines are in air (20% oxygen).

After each shorting described above, the energy harvester was allowed to rest for one hour, in oxygen. FIG. 10 shows the energy harvester recovery. The energy harvester consistently recovered after dead shorting—even after 25 hours of continuous shorting.

Next, the energy harvester was allowed to rest in various atmospheres. FIG. 11 shows the results of this experiment the energy harvester started in air (20% oxygen), then after about 5 minutes, the atmosphere was changed to pure oxygen and the current density rose from about 30 mV to about 70 mV. Then, at about 20 minutes, the atmosphere was changed to pure argon (0% oxygen) and the potential dropped to zero, then even below that. Next, at about 4 hours, the atmosphere was returned to open air (20% oxygen) and the potential returned to about 45 mV. This shows the strong effect of external gasses on the performance of this energy harvester.

Next, a dead short was done in the various gasses, and FIG. 12 shows the resulting current densities under the three gas environments as a bar graph. The currents are cathodic, resulting in negative values, thus requiring multiplying by −1 as shown in FIG. 12. A strong effect of the atmospheric presence of air is seen in the first bar, then in oxygen (second bar) and finally in argon (0% oxygen) (third bar).

FIG. 13 provides a voltammogram for the energy harvester 28716.4 (14 Oct. 2016, cell #4) showing a current density of 170 uA/cm² and an exchange potential of nearly 100 mV after allowing the energy harvester to rest for 48 hours in air. The voltammogram also shows 5 nW/cm² at 0.066 volts. This data is not impedance compensated.

FIG. 14 shows the AC impedance of this energy harvester is acceptably low. The compression of the pellet and the nickel cross-bonded expanded metal current distribution both help the impedance issue. FIG. 15 is a Nyquist plot of this energy harvester, showing a large charge-transfer resistance (R_ct) of 18.8 kΩ.

Example 6: Excluding Water as Liquid Electrolyte

Water absorption improves functionality. To test whether water is a liquid electrolyte, an energy harvester was constructed using five (5) layers of dry nickel expanded metal inserted between the electrodes of FIG. 16 showing the anode (7A1), 5 expanded metal disks (1601), separator pellet (7A2), five more expanded metal disks (1601) and cathode pellet (7A3). The source for the electrodes was the well-tested energy harvester above. Then, while under pressure, the anode and separator was re-epoxy sealed (7A5) from any external contact with air, leaving the cathode pellet (7A3) exposed to the air. The energy harvester was re-assembled and tested. In this example, electrons and gasses, but not ions, are allowed to pass between the electrodes. The pellets were made according to the Example 1 above.

FIG. 17 shows two Voltammograms of these energy harvesters 30616.1 (2 Nov. 2016, cell #1). The top line is with electrodes nestled together and the lower line shows the performance with 5 expanded metal disks separating each electrode. Even without any possible ion movement between electrodes, the energy harvester performed, demonstrating that such ion movement is not required and charge is indeed passed vie electrons and perhaps on charged gas molecules, but not as ions.

FIGS. 18A and 18B are graphs of a set of shorted discharges and OCV spontaneous recharges all done in air (20% oxygen). The discharge set is shown in FIG. 18A where the top line is the energy harvester with the electrodes in intimate contact and the lower set of lines shows performance with the five layers of expanded metal placed between the electrodes. Clearly, performance continues without ionic transport, but only electrons and perhaps charged gasses.

FIG. 18B is the same set, but for the voltage recovery after one hour discharges. Again, the top line is the energy harvester with electrodes in contact with one another and the lower set are several recharges with the electrodes physically separated from one another. Again, the performance is clear even with no ionic transport of charge. This energy harvester transfers charge only vie electrons.

These experiments with electrodes isolated one from the other, but allowing electrons and gasses to pass freely, demonstrate that charge is being passed between the electrodes using only electrons or charged gasses. The ionization of oxygen occurs within the individual electrodes (using water vapor as a reagent), with oxygen being passed as a gas as electrons move from each cathode toward the anode.

The increased performance when assembled in closer proximity of the electrodes to each other is a physical advantage, not an electrochemical advantage.

Without being bound by theory, it is believed that water present in the energy harvester acts not as an electrolyte, but rather as a reagent within individual electrodes.

Example 7

FIG. 19 shows a 3-layer thin-film energy harvester was prepared as described in Example 2A and 2B above using the rolling mill as described in FIG. 8 (run number: 36416). Gold plated 10-mil brass shim stock 1-inch diameter disks (7B1 and 7B2) placed between each thin layer anode (7A1), separator (7A2) and cathode (7A3) between a pair of gold plated current collector (7B1 and 7B2) sheets were used.

FIG. 20 shows a voltammogram of the separated-electrode energy harvester described in FIG. 19, with the curve from the 3-layer thin rolled electrode energy harvester, wherein the electrodes were simply pressed on top of each other with no spacer. The top line had gold plated brass spacers between the electrodes. The lower line was built with no spacers at all, but electrodes pressed together. It showed a lower the voltage, but a decade higher current density. Both energy harvesters performed, but with different resulting parameters. Total blocking of liquids, ions and gasses clearly did not hinder performance, demonstrating that this energy harvester transfers charge using only electrons.

FIG. 21 shows a long OCV of this thin electrode energy harvester with solid spacers between electrodes for cell 36516 (31 Dec. 2016). This energy harvester was exposed to oxygen in the beginning where the OCV reached 0.12 volts, then sagged a bit, but still held a voltage. T about 700 minutes, it was given more oxygen and the performance improved again. It should be noted that the environmental “chamber” is simply a plastic bag with cable ties closing the top. This is not a hermetic seal by any means. So atmospheric gasses do diffuse in over time. At about 825 minutes, argon was made to fill the bag and a precipitous drop in performance was observed. At about 875 minutes, oxygen was reintroduced to the “chamber” and performance again rebounded. These results show that the energy harvester still functions whether the electrodes are sandwiched together or separated with an impervious layer of nickel. This indicates that one could roll or paint the active ingredients onto a metal foil to increase the surface area.

Example 8

FIG. 22 shows a cross-section of a 3-layer energy harvester made using the Teflon rolling mill method described above in Example 2B. In this case, each electrode is a different diameter with the bottom layer being the cathode at 1″ (25.4 mm) diameter (7A3), the separator being ⅞″ (22.2 mm) (7A2), and the anode being ¾″ (19 mm) (7A1). A paper insulator is made to be sure the current collector does not short the anode and separator (2201) to the current collector disks (7B1 and 7B2). This ensures that there is no accidental shorting between the anode and the cathode or even direct shorting of the energy harvester. The energy harvester was subjected to various tests, where it performed the best of all previous tests.

Shorting tests: FIG. 23 shows the current density for three 24-hour dead shorting tests of cell 24417 (1 Sep. 2017). The current density is now much higher than previous tests using the thin electrodes with progressively smaller electrodes to prevent accidental shorting between electrodes. Several conditions, such as changing the gasses can be seen in these lines. Consider the lowest line, which was the initial discharge. The energy harvester was dry after manufacturing. Near 90% of the test, it was exposed to 100% relative humidity (RH) and it's performance improved considerably. The next line above that, shows a continuation of the same energy harvester in air and 100% RH until 20% of the test where pure oxygen is introduced. At about 25%, pure argon was introduced to remove all oxygen from the test chamber. At 85%, atmospheric air was introduced (20% oxygen). The top line was after house of rest in 100% RH air and at the end of the 24-hour test, oxygen was introduced, giving a considerable increase to the current density output. The effect of atmospheric oxygen is clearly evident in the resulting open circuit voltage with oxygen giving the highest value.

OCV Recovery Testing: FIG. 24 shows the OCV after each of the long discharges in FIG. 23. The lowest line shows OCV recovery in argon (little oxygen). Remember that the test chamber is not fully sealed from contaminating oxygen from the air. The middle line is in air and the top line is in 100% oxygen. Again, clearly, the atmospheric gasses are playing a large role in performance.

FIG. 25 summarizes the OCV between the tests from the graph shown in FIG. 24. The light gray bar shows the rate of increase rate (i.e., initial slope of recovery) and the dark bar shows the voltage reached after 30 seconds.

The energy harvester was tested on mostly 24-hour dead short discharge cycles and changing rest times. FIG. 26 shows the dead-short discharges for the life of this energy harvester (run number 24417) plotted in the order of the tests. Most of the bars are the current density at the end of a 24-hour test in 100% RH air. The two grey bars #4 and #5 were discharged in oxygen for an hour each. The fifth from the last (#20) is a 12-day discharge in 100% RH air. The fourth from the last (#21), was a series of environmental gas changes. The longest discharge is shown by the last bar (#24) showing the current density after 5 days of discharge. It increased the current output over time. The energy harvester appears to self-recharge as it discharges. The total discharge of this energy harvester during this series of tests of 560 hours (23 days), delivering 1.5 Coulombs.

The last bar in this test was repeatedly interrupted to take impedance values. FIG. 27 shows this long discharge over many days of discharge with changing atmospheric gas composition. The discharge was interrupted several times for a few minutes to measure the impedance numbers (as shown later in FIG. 29). In this long test is a period of gas testing starting with a desiccated condition, followed at about 24 hours 100% RH air environment. After 12 days, a series of gas tests were run discussed below with FIG. 27. Then at about 290 hours (12 days), the chamber was filled with argon to displace the oxygen.

FIG. 28 provides exemplary results with air in the first portion, followed by oxygen at about 294.5 hours (12.25 days) where the output increased. This was followed by argon displacing oxygen at about 294 hours. Then air was introduced 30 minutes later until about 300 hours when argon was introduced. This was followed by many applications of argon due to the constant diffusion of atmospheric air into the test chamber. Again, the importance of oxygen is shown for this energy harvester.

With respect to FIG. 27, the chamber was re-filled with 100% Rh air and run for an additional six days. It not only fully recovered, but gave higher current density after the test. This cell ran for almost 20 days with no degradation and the current density improved over the course of the testing.

FIG. 29 shows the 65 kHz AC impedance as a function of the current density of the energy harvester as it humidifies from desiccated to water saturated conditions. There is a semi-logarithmic relationship (with a R2 value of 99%), which shows that it is a first-order relationship. Without intending to be bound by theory, this appears to indicate that water ingress caused the change in impedance as the current density increases. In this example, AC impedance is lowered, which increases the current density.

Example 10

A 3-layer energy harvester was made using the Teflon rolling mill method described above in Example 2B: Rolling Electrode. In this example, the Teflon (PTFE) was added as a water suspension called Teflon 30. These particles are very small compared to the T7c powder described before.

The recipe for this 12-gram mixture was:

TABLE 3
Molecule	CeO2	WO2.9	Ti4O7	CO3O4	T30	H2O	Units
Anode	2	4	6		2.76	1.5	g
Separator	4	8			2.066	0.84	g
Cathode	2	4		6	2.421	0.33	g

In this aspect, 40 volume percent Teflon was added to each electrode as was used for the Teflon 7C.

The procedure was as follows:

• • 1) Weigh the active powders as usual, but with no Teflon 7C (alternatively, Teflon F-104 can be used).
  • 2) Place powders in a 100 cc beaker and add 50 cc distilled water
  • 3) Insert a stirring bar and bring to a deep vortex without sucking in air
  • 4) Add the Teflon emulsion T30 drop wise
  • 5) Allow to stir for about 30 minutes
  • 6) Prepare a Buckner funnel and filter the slurry under high vacuum
  • 7) Place the filter paper with the filter cake still attached into a glass dish
  • 8) Place in a drying oven at 120° C. until dry (˜6 hours for this 12 gram recipe).
  • 9) Alternatively, place in a desiccator at room temperature until dry (˜24 hours).
  • 10) Scrape the dry cake from the paper and grind in a high-shear blender after adding the small aliquots of water in the recipe.
  • 11) Use a rolling mill to form the electrodes.

The resulting electrodes were more robust than the dry method, and formed an energy harvester rather easily.

FIG. 30 shows the limiting current taken from the initial voltammogram after building several energy harvesters. The first bar shows the limiting current (LC) of a new energy harvester using the dry Teflon 7C binder before humidification. The second bar shows the LC after humidification. The third shows the initial performance of the energy harvester made using the liquid emulsion T30 binder, removing the water via evaporation.

Without wishing the invention to be bound by theory, FIG. 31 generally illustrates the charge flow of an exemplary energy harvester described herein. It is believed that oxygen enters cathode 7A3 carrying its two negative charges (electrons). The oxygen nestles into the crystal structure and defects of cathode material 3101 (e.g., Co₃O₄), making an excess of electrons that slide onto the CeO₂ crystals with their loosely bound oxygen atoms, carrying two electrons with them. These electrons are free to migrate to separator layer 7A2, being attracted by the lower electronegativity of the WO_2.9, and facilitated by CeO₂ “electrolyte” 3102. The transition metal suboxide (e.g., Ti₄O₇) in anode 7A1 has a greater electronegativity than Co₃O₄ 3101 of cathode 7A3. These electrons are released by the oxygen reacting with hydroxyl ions, forming water vapor in anode body 3103, which escapes into the environment. Current collector 7B1 accumulates the excess electrons forming a potential across load 3104, returning the electrons to cathode current collector 7B2.

Layer 7A2 is optionally not included.

Example 11

Low impedance, three-electrode design:

In this aspect, the cell uses a high impedance portion to separate the charge. For example, the anode and cathode can comprise carbon (e.g., black or graphite) to reduce the impedance of the electrodes while retaining the high impedance in a layer of SSE situated between the electrodes as a solid-state separator (FIG. 32). In another aspect, Ti₄O₇ is added to the SSE to increase the DC resistance. In this aspect, the power density can be increased by about 10-fold.

In the exemplary aspect of FIG. 32, “A” is the anode and composed of the active compounds plus carbon, “Sep” is the SSE, and “C” is the cathode plus carbon. In another aspect, carbon loading can be about 5%. In another aspect, Ti₄O₇ or other impedance-increasing component can be added to the SSE separator layer to increase its resistance. The carbon is preferably nano-sized acetylene carbon black powder. The carbon was tested in the form of carbon black using CABOT Vulcan XC72R (also called simply “V72”) and alternately Asbury Graphite Mills “Nano 307” powdered graphite. Loading below 5% is best, but even 0.5% is beneficial. Also tested was a mixture of the two carbon types.

The DC resistance of the components was measured to better understand the impedance character the exemplary cell. Table 4 shows the DC resistance of the cell components. Components 1-4 are the raw chemicals, components 5-6 are the anode without and with carbon, 7 is the SSE and 8 & 9 are the cathode without and with carbon. Items 5-9 all also contain 40 volume percent unsintered Teflon powder.

TABLE 4
Component & Electrode Ohm-cm
#	Material	Dry
1	Ti4O7	2,977,662
2	Co3O4	24,615
3	WO2.9	4.96
4	CeO2	63,300,000
5	Anode	1,488,843
6	Anode w/Graphite	393
7	SSE	205,213
8	Cathode	12,320
9	Cathode w/Graphite	149

FIG. 33 shows that the exemplary three-layer design produces a 12.5 times higher discharge rate than 34818 cell (14 Dec. 2018). which was the highest tests before with no carbon in the electrodes. This cell was a two-electrode design.

FIG. 34 shows the dead short discharge of a cell with and without carbon in the electrodes with an eight (8) fold increase in current density.

As shown in FIG. 35 shows a potentiostatic discharge of the cell, beginning in humid air (20% oxygen), then at 4.5 hours in 100% humid oxygen. At 6 hours, the gas was changed to humid argon (0% oxygen) and at 12 hours back to humid air. In this aspect, it appears that oxygen content influences the output. Without being bound by theory, the fact that an argon atmosphere does not reach zero suggests that water vapor is being electrolyzed to produce its own oxygen in situ.

FIG. 36 shows the power curve for three example designs. The bottom curve is for a two-electrode design and contained no carbon. The top two curves are three-electrodes designs one with 3% nano graphite and the other with 3% Vulcan 72 carbon black added to the anode and cathode with a SSE layer between the two for separation of charge across it's relatively higher impedance.

Next, carbon black was used in the anode and cathode at the same loading levels as the graphite was in the previous run. After “activation” (shorting for 24 hours, then OCV for 6 hours) this cell with carbon black was a bit higher in power density than the graphite, but graphite achieved a slightly higher exchange potential. In another aspect, carbon black and graphite can be mixed in the electrodes.

In one aspect, carbon can be added to the anode and cathode at between about 2% to about 6%. In another aspect, the amount of carbon added to the anode and cathode can be about 4%.

Example 12

These electrodes can be produced using a painted method if the binder is liquid based that will then be removed. A painted energy harvester was developed using a 25% dilution of a latex medium (lot 03717). Each electrode was rolled material that was then re-ground to chop up the fibrillated Teflon fibrils. The resulting mixture was then mixed 50/50 with a 25% solution of latex binder resulting in a thick paint-like material. The paint-like material was painted on to a 1 mil sheet of nickel that had previously been painted with a thin coat of 50% diluted Timrex LB1016 graphite conductive paint. Each electrode was dried between applications. The final thickness was just 12 mils (0.012″ or 0.3 mm). Discs were then blanked out using a ¾″ arch punch. The resulting energy harvester proved feasibility, but delivered low current density values compared to the rolled or pellet methods.

Example 13

An exemplary low impedance, three-electrode design with gold-plated current collectors, nano powder size and carbon additive was tested.

In this aspect, the cell uses a high impedance portion to separate the charge as described in Example 11. In this example, the anode current collector had a heavy gold plating on the brass sheet current collector, and the cathode used a porous carbon fiber (Sigracet 25 BC from FuelCellStore.com) cloth current collector. Without being bound by theory, it is believed that carbon fiber cloth current collector permitted airflow into the cathode, but not the anode resulting in an unexpected increase in performance.

In this example, the anode mixture is ground in a high sheer blender for about 5 minutes, and then the carbon is hand mixed until the mixture appears uniform in color (e.g., about three minutes), similar to “folding” in egg whites in a cake mixture. The same procedure is applied to the cathode powders (e.g., the SSE is blended in a high sheer blender, but no carbon is added).

FIG. 37 shows the performance improvement in three steps as polarization curves expressed as Voltammograms.

Scan c was generated from the cell providing the previous best results. Scan b was generated from a cell with the carbon additive to the anode and cathode during high sheer grinding and increased current density by 3.7-fold compared to the lowest scan. Scan a was generated from a cell that included 2% V72 carbon black added to the anode and cathode using the gentile folding method resulting in a 38.4 fold increase in current density. All components in this cell were nano sized except the carbon, and the cathodic current collector was porous carbon paper with the anode heavily gold-plated brass current collector. The carbon paper for this and other embodiments may advantageously be Sigracet 22 BB, which may be obtained, for example, from The Fuel Cell Store (fuelcellstore.com).

Example 14

FIG. 38 shows the performance improvement from the three-electrode design of Example 13 showing the first derivative of the polarization curve (i.e., the power vs applied potential curve)

Scan c was generated from the cell providing the previous best results. Scan b was generated from a cell with the carbon additive to the anode and cathode during high sheer grinding and increased power density by 5.7-fold compared to the lowest scan. Scan a was generated from a cell that included 2% V72 carbon black added to the anode and cathode using the gentile folding method resulting in a 110 fold increase in current density. All components in this cell were nano sized except the carbon, and the cathodic current collector was porous carbon paper with the anode heavily gold-plated brass current collector.

Example 15

A series of water glycerin mixtures was used to generate humidified air for testing of the exemplary well-functioning three-electrode cell on a dead-short discharge. FIG. 39 shows the resulting output (i.e., current density). At 85% RH, the ultimate performance is 50% of its maximum at 100% RH. In one aspect, increasing the relative humidity (e.g., above 50%) can increase the current density.

Example 16

In this example, cells were prepared with the active component of Ti₄O₇ in the anode and Co₃O₄ for the cathode. One cell used an activated Nafion™ (sulfonated tetrafluoroethylene based fluoropolymer-copolymer having a chemical formula of C₇HF₁₃O₅S·C₂F₄) separator (see DuPont Product Bulletin P-11 “Nafion™ NR211 and NR212” at www.nafion.com/en/-/media/files/nafion/nafion-nr211-nr212-p-11-product-info.pdf?rev=b3a97676150d4db5b4cd7518491a8f94), which transports only protons (H⁺). Another cell was prepared with an AEM-215-30 Anion Exchange Membrane (AEM) separator. The exemplary cell having the Nafion™ separator ran at 13 times higher current output when using Nafion™ than when using AEM. Without being bound by theory, it is believed that that the charge-transfer involves proton transport from the anode to the cathode and not hydroxyl groups (OH⁻). In one aspect, the exemplary three-electrode design can use a Nafion™ separator to achieve higher current output.

Example 17

FIG. 40 shows the Specific Power Density of the active components. In FIG. 41, exemplary cells using only the active components (Ti₄O₇ and Co₃O₄) (411) were compared to a control mixture of active components and an SSE separator (CeO₂ & WO_2.9). As shown in FIG. 40, the combination of the exemplary active components and the SSE separator between about 20 and 70% more specific power. In this example, cells can be made with only the active components (Ti₄O₇ and Co₃O₄), however with the SSE (CeO₂ & WO_2.9) performance is surprisingly improved (e.g., 3 times more power density and 4 times the specific power). Without being bound by theory, it is believed that the SSE in this example behaves catalytically or functions in active transport of oxygen molecules.

Example 18

Cells were prepared using exemplary layered electrodes to double, triple and quadruple the electrode thickness. In this example, a single electrode was 0.23 mm thick. The thickness series used was 0.23 mm, 0.46 mm, 0.69 mm and 0.92 mm. As can be observed in FIG. 41, the performance was improved by about 70% up to three layers (0.69 mm) with about a 50% improvement at 0.92 mm. 0.46 mm provided about a 10% improvement. In this example, the power density performance of the cells showed that thicker electrodes surprisingly improved performance to a limit: 0.23 mm<0.46 mm<0.69 mm=0.92 mm.

Example 19

Assembly Modes and Methods: In one aspect, this energy harvester is assembled as follows:

• • a. A solid anodic current collector, which should be of a material that does not react with the active ingredients. This could be nickel, gold, gold-plated metal or carbon and should cover most or the entire anode surface.
  • b. An anode composed of an admixture of the solid-state electrolyte and a suboxide of a transition metal. The physical form of this layer is compressed and held together using a porous binder. It may also be applied as a paint using a liquid binder that is dried after application.
  • c. A layer called a “separator” consisting of only the solid-state electrolyte and the binder. It may be the same thickness of the anode and cathode, or it may be thinner than the anode and cathode or it may be missing all together.
  • d. A cathode composed of the solid-state electrolyte and a suboxide of a transition metal, which is less electronegative than the suboxide used in the anode.
  • e. A cathode current collector, which should be of a material that does not react with the active ingredients. This could be nickel, gold, gold-plated metal or carbon, and should cover most or the entire cathode surface. This layer is preferably porous, such as foamed metal, perforated metal of porous carbon.

Example 20

Binders: In this example, the powders described herein are not sintered, but rather bound together using a binder. They are therefore “green” (unsintered). Binders that may function in this energy harvester include fibrillated Teflon (PTFE), Latex, albumen, hydrogels, aerogels, or other organic or inorganic binders with low conductivity. The material needs to be porous and have very high internal impedance; higher than the active ingredients of the invention. The binders may start with a solvent that when dried, results in a high impedance, high porosity binder.

Example 21: Grommets and Cellulose Separator

Exemplary Applications: This energy harvester can be used in low-power applications where there is a constant source of atmospheric air. Preferably this air is moving, such as in the flow from a ventilation fan or on a moving vehicle. If on a digital watch, the energy harvester case will need to be porous for air access. Examples include the list below among others:

• • a. Gas sensors, due to its sensitivity to atmospheric gas composition,
  • b. Any low-power device such as electronic watches, low-power LEDs,
  • c. Any place with constant air movement such a moving vehicle, within the flow of a cooling or ventilation fan, on the blade of a windmill, upon the wing of an aircraft among many others.
  • d. Painting the anode portion on a solid surface with subsequent layers painted over it, terminating with some porous current collector would result in a large surface area, high current output for many applications.

Additional energy harvesters in accordance with aspects of the present invention may also be used in implementing the exemplary applications listed in Example 21 above. Examples of such further energy harvesters will now be discussed.

The further energy harvesters may retain many of the features of the previously discussed energy harvesters, e.g., Example 2A. For example, the retained features may include (1) the powder mixing method (high sheer of all but the carbon, which is hand mixed), (2) all components in the nano size, (3) use of a powder chute to slightly pre-compress the powder before rolling the electrode, and (4) cells tested under 125 pounds force.

The further energy harvesters may include variations/changes from the previously discussed energy harvesters. These may include, but are not limited to, (1) a new formulation that does not include CeO₂, (2) a new assembly method using an electrode grommet and a pre-compression step. (3) a new separator, using no SSE, but rather a separator made of a cellulosic material, where a cellulosic material may be cellulose (optionally hydrated and non-plasticized) cellophane, rayon, or another cellulose-derived or viscose derived material, (4) a new cell body, in which all or substantially all air ingress is from the surface of the cathode, with the anode being mostly sealed off from gas movement, and (5) the cathode current collector (transfer layer) is a fine stainless-steel screen rather than a gold-plated brass disk with a tail as used before.

One embodiment of such an energy harvester is shown in FIG. 42 and has the following construction.

FIG. 42 shows a five-layer design for a cell. The cell includes an anode pellet 4201 and a cathode pellet 4202. Both the anode and cathode are enclosed within a plastic grommet 4203, as also shown in FIG. 43. Polypropylene works well for the material of the grommet, but nylon and any other plastic that is stable in moist environments would work. A cellophane sheet 4204 separates the two electrodes. Advantageously, this is non-plasticized cellophane, however a plasticizer that encourages moisture transport would also work very well. Most cellophane plasticizers are used to increase strength and to make the sheet waterproof, which is not a feature of this cell structure. Both cellophane that is filled with silver and that which is not have been tried, and both work well. The cellophane is cut and soaked in distilled water for several hours. It is then removed from the water, gently daubed off between two dry paper towels, and then is sandwiched between the grommeted electrodes. Then an anode current collector is made of gold-plated brass 4205. The cathode has a layer of porous carbon paper (e.g., Sigracet 22 BB) 4206. Over this is a very fine mesh stainless steel screen cathode current collector (TIMESETL 304 Stainless Steel Woven Wire 200 Mesh) 4207. All humid air enters the cell via an open grid pattern 4208 in the cell body. As in previous designs, the cell body (not shown) is made of polypropylene, but any moisture resistant material would do.

In this Example:

Anode: The anode is composed of 83% nTi₄O₇+17% nWO_2.9. The ratio may be a bit higher in WO_2.9, but not too much. This is bound with 40 volume percent Dalkin F104 Teflon Binder (powder), and then 2% nano-sized acetylene carbon black powder, preferably Vulcan XC 72R or Nao 307.

Separator: The separator may be, e.g., one of hydrated, non-plasticized cellophane and a proton exchange membrane. The cellophane may be silver filled and or not silver filled.

Cathode: The cathode may be composed of 70% nWO_2.9+30% Co₃O₄ (AKA W₂₀O₅₈). Alternatively, the cathode may be composed of 72% nWO_2.9+28% Co₃O₄ (AKA W₂₀O₅₈). The cathode is bound with 40 volume percent Dalkin F104 Teflon Binder (powder), and then 2% nano-sized acetylene carbon black powder, preferably Vulcan XC 72R or Nao 307.

Generally, the cell assembly may comprise the following layers:

• • (1) A cathode current collector. This is a 27 mm disk, and it may be made of Sigracet 22 BB Carbon paper that is 0.2 mm thick.
  • (2) A cathode disk and grommet assembly.
  • (3) A hydrated cellulose disk.
  • (4) An anode disk and grommet assembly.
  • (5) A gold-plated brass disk that is 27 mm in diameter.

A cell may be constructed by a method in accordance with aspects of the present invention.

The electrode powders for the anode or cathode are weighed into a 250 ml plastic beaker. The Daikin F104 Teflon powder is then added. The powders are mixed with a high sheer grinder at ˜20,000 rpm for at least one minute, and about 2 minutes. A Krups® F203 coffee grinder is suitable for this purpose. The mixed powders are allowed to rest for a few minutes to let the dust settle. The mixed powders are weighed to calculate the carbon loading. Then the nano-sized acetylene carbon black powder is added and hand mixed with a flat spatula for at least 2 minutes, and preferably for about 3 minutes.

The resulting powder is pre-compressed in a paper-lined compression chute. First, a strip of paper is laid on the chute, and the powder is sprinkled onto the paper strip to about 3.5 mm depth. The powder is leveled with a wide plastic spatula using the edge like a knife at a 45° angle to the powder. The leveling is done back and forth to get the powder very even and slightly compacted on the rails of the chute, to about 2.0 mm (or 2.5 mm) depth. A second strip of paper is laid on top.

This arrangement is then compressed under about 2000 pounds compressive force using, for example, a rolling mill between two Teflon-coated steel sheets. Using, for example, the spatula, the powder and paper arrangement is lifted and placed on the first steel sheet and placed on the entry platform of the rolling mill. The rolling mill is set to 25 psi, with two 4″ pancake cylinders delivering just over 1000 pounds force at that pressure. The second steel plate is placed over the arrangement, which is then rolled through the mill. Then the arrangement is placed on a clean work sheet and the two strips of paper are removed.

The result is a strip of electrode about 180 mm inches long and about 0.09 mm thick. From this, electrode disks are blanked out using an arch punch or equivalent.

The electrode grommets were 3D printed using PETG filament. FIG. 43 is a cross section of that part. The ID of the grommet is 25 mm and the OD of the disk is 22.25 mm. When they are then compressed under 2000 pounds force between parallel plates, this expands the electrode in OD to compress within the grommet while reducing the thickness of that part as well. The result is a strong, uniform part that is easily assembled. The OD of the assembled part is 28 mm.

This is done for both the anode and cathode electrodes.

The cellulose separator is blanked at 27 mm, so it totally covers the active electrode and is easily placed over the electrode-grommet assembly.

The cellulose sheet is blanked is placed on a soaked paper towel. A second paper towel is placed over this, and the flooded mass is allowed to sit for at least 16 hours. The paper toweling is to hold them under the distilled water.

When it is time to use the cellulose, it is tweezed out of the dish and placed on a dry paper towel and momentarily daubed to remove any standing water.

The cell may then be subjected to testing.

The tester supplies all humid air from the cathode side of the cell with no clear exit, but the cell is not hermetically sealed. This holder is shown in 3D CAD image in FIG. 44. The incoming gas flow is from the bottom, facing the cathode. The holder is also shown in cross section in FIG. 45, showing the interconnection of the honeycomb pattern airflow manifold. Not shown is the cathode current contact, which is a very fine stainless steel screen disk with a tail extending out for electrical contact. Also not shown is the anode current contact, which is a gold plated brass disk with a tail extending out for electrical contact.

The cell assembly, comprising layers 1-5 described above, is placed into the cell testing body. This supplies all airflow from the cathode side of the cell and limits any gas movement into or out of the anode.

The chemical mechanism discussed below suggests that oxygen is used in the cathode, but not by the anode. There is oxygen gas exhaled from the anode, but at very low rates, so gas entrapment is very unlikely.

The assembled cell is then placed in a test apparatus that applies about 125 pounds force. This would not be necessary if the cell were built into a discrete component.

While not wishing to be bound by theory, the following Mechanism 3 may be relevant. This explanation describes the current understanding of the chemical mechanism and environment.

Mechanism 3

In the following explanation, a symbol in BOLD means it is in from the environment (H₂O vapor) or external circuit (e⁻). A symbol in ITALICS means it is soluble or mobile within the cell (H₂O_v, H₂O, and H⁺). A symbol in UNDERLINE means it leaves the cell (O₂ from anode, e⁻ from anode, H₂ from cathode).

Anode (TiO_x and WO_2.9):

$H_2{O}_v+{\mathrm{TiO}}_x-->{\mathrm{TiO}}_x{\mathrm{OH}}^{-}+H^{+}-->{\mathrm{TiO}}_x+1/2O_2+H^{+}+\underset{\_}{2e^{-}}$

Or simplified to

$H_2{O}_v\stackrel{\mathrm{TiOx}}{--}>\underset{\_}{1/2O_2}+2H^{+}+\underset{\_}{2e^{-}}$

The TiO_x is catalyzing the dissociation of the water molecule. We propose with vacancies (“V”) shown:

${\mathrm{Ti}}_4{O}_{7}V+H_{2}O-->{\mathrm{Ti}}_4{O}_7{O}^{-}+2H^{+}-->{\mathrm{Ti}}_4{O}_{7}V+\underset{\_}{1/2O_2}+2H^{+}+\underset{\_}{2e^{-}}$

WO_2.9 mechanism

$\left(W^{+6}-V-W^{+6}\right)+H_{2}O-->{\left(W^{+6}-O-W^{+6}\right)}^{=}+2H^{+}-->{\left(W^{+6}-V-W^{+6}\right)}^{=}\underset{\_}{1/2O_2}+2H^{+}+2e^{-}{H}_2{O}_v<\stackrel{\mathrm{WOx}}{--}>\underset{\_}{1/2O_2}+2H^{+}+2e^{-}$

The second reaction is reversible.

The anode exhales O₂ and liberates electrons. It does not inhale oxygen.

Separator:

The proton exchange membrane Nafion 211 works well, as does non-plasticized “battery-grade” cellophane. This works well due to:

• • Easy proton transfer (for Nafion™) and all ions for cellulose.
  • No electron loss through the SSE layer. All electrons must pass through the load.Cathode (Co₃O₄ and WO_2.9):

WO_2.9 mechanism. This is the reverse of the anode reaction. It needs oxygen from the air and electrons from the external circuit.

$\left(W^{+6}-V-W^{+6}\right)+H_{2}O<-->{\left(W^{+6}-O-W^{+6}\right)}^{-}+2H^{+}<-->{\left(W^{+6}-V-W^{+6}\right)}^{=}1/2O_2+\underset{\_}{2H^{+}}+2e^{-}$ $\left(W^{+6}-V-W^{+6}\right)+H_{2}O<-->{\left(W^{+6}-O-W^{+6}\right)}^{=}+$ $2H^{+}<-->{\left(W^{+6}-V-W^{+6}\right)}^{=}\underset{\_}{1/2O_2}+2H^{+}+$ $2e^{-}+2H^{+}-->{\left(W^{+6}-V-W^{+6}\right)}^{=}1/2O_2+2H^{+}+$ $2e^{-}<-->{\left(W^{+6}-O-W^{+6}\right)}^{=}+2H^{+}<-->\left(W^{+6}-V-W^{+6}\right)+H_{2}O$

Or simplified:

$1/2O_2+2H^{+}+2e^{-}<\stackrel{\mathrm{WOx}}{--}>H_{2}O$

The oxygen is from air, in a reversible reaction.

Co₃O₄ set (This does not require external oxygen, just H⁺ and 2e⁻)

$2{\mathrm{Co}}_3{O}_4+2H^{+}+2e^{-}-->2{\mathrm{Co}}_3{O}_4+\underset{\_}{H_2}$

Or simplified to

$2H^{+}+2e^{-}\stackrel{\mathrm{CoOx}}{--}>\underset{\_}{H_2}$

Mechanism for the Co₃O₄ Catalysis of Water Dissociation:

${\mathrm{Co}}_3{O}_{4}V+H_2{O}_v+2H^{+}+2e^{-}-->{\mathrm{Co}}_3{O}_{4}O+1/2H_2+3H^{+}-->{\mathrm{Co}}_3{O}_{4}V+H_{2}O+\underset{\_}{H_2}$

Or expanded:

Co₃O₄ is valence +4 cobalt and a cobalt +3 with four resident oxygens and a vacancy (or two).

${\left(O_2^{-4}{\mathrm{Co}}^{+4}-V^{+1}-{\mathrm{Co}}^{+3}{O}_2^{-4}\right)}^0+H_2{O}_v+2H^{+}+2e^{-}--->{\left(O_2^{-4}{\mathrm{Co}}^{+4}-O^{-2}-{\mathrm{Co}}^{+3}{O}_2^{-4}\right)}^{-3}+\underset{\_}{1/2H_2}+3H^{+}--->{\left(O_2^{-4}{\mathrm{Co}}^{+4}-V^{+1}-{\mathrm{Co}}^{+3}{O}_2^{-4}\right)}^0+H_2{O}_v+\underset{\_}{H_2}$

The cathode exhales H₂, accepts electrons, and inhales O₂.

This explains why running in oxygen is best, air is good. and argon (i.e., no oxygen) still performs, but not as well.

FIG. 45 is a pictorial representation of what comes into the cell, what comes out of the cell, and what passes through the cell.

{This figure will be placed in the drawings in the final version of the spec, with a change from color coding to emphasis.}

		Anode
		H2Ov	--> O2
		H2O H+	--> e− to load
			Cellulose
	H2Ov -->	H2O H+	<-- e− from load
	O2 -->	H2Ov	--> H2
		Cathode

Entering the cell: The cathode inhales water vapor (H₂O_v) and oxygen (O₂). The cathode accepts electrons (e⁻) from the load.

Internal charge transfer is the protons (H⁺) produced in the anode and transported within liquid water (H₂O) on the surfaces. The driving force is both from Knudsen diffusion and the concentration gradient. Water vapor (H₂O_v) is also free to move within the porous body of the electrodes.

Leaving the cell: Oxygen (O₂) from the anode and hydrogen (H₂) from the cathode are exhaled in gaseous form. Electrons (e⁻) leave the anode to do work in some load and return to the cathode.

Unless indicated otherwise, potentials (E_o) reported herein are from the following source: en.wikipedia.org/wiki/Standard_electrode_potential_(data_page).

The term “energy harvester” used herein is not limited in a mechanical way to be an enclosed body with electrodes, but may be open to the environment on one of more sides of the device. The term “solid state energy harvester” may be interpreted as a “solid state energy source.”

This device may function as an energy storage unit such as a battery or as a capacitor.

Example 22

This example demonstrates aspects of the invention that can use water vapor to generate power with no need to be exposed to air. Applications of this embodiment include nonlimiting subdermal applications such as Deep Brain Stimulators, intraocular pressure monitors, artificial urinary sphincters and bone healing applications. Such applications provide a steady temperature (e.g. 37° C.), 100% RH environment, however, there is no oxygen. So, a new cell housing was developed to exclude all atmospheric oxygen, establishing that the invention can operate in an anoxic environment.

Materials

Porous Teflon tape: Saint Gobain DoM 30/23/00/Natural or equivalent.

Fine nickel cloth: TIMESETL 304 Stainless Steel Woven Wire 200 Mesh (see amazon.com/gp/product/B081QB3BLF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1) or equivalent.

Closed-cell porous neoprene compressible gasket material: Neoprene soft gasket material, McMaster Carr #93375K402 or equivalent.

Conductive paint: MTN Water Based 300 Spray Paint-WRV9011-Carbon Black

In this example the cells are assembled in a manner similar to other Examples herein, with the major difference being that the cell is excluded from ambience. Specifically:

• • The anode is 77% nTi₄O₇+23% nWO_2.9+40 v/v Teflon Binder, which are blended together in a high-sheer grinder. Then 2% nCarbon Black (V72) is admixed.
  • The cathode is 70% WO_2.9+30% Co₃O₄ (AKA W20058)+40 v/v Teflon Binder, which are blended together in a high-sheer grinder. Then 2% Carbon Black (V72) is admixed.
  • More specifically, the powders were blended at 20,000 rpm blender for 2 minutes, then the Carbon Black (V72) was admixed for about 3 minutes.
  • The powder is sprinkled onto a paper-lined compression chute to about 3.5 mm depth and smoothed & pre-compressed to about 2 mm depth. This is then compressed under about 2000 pounds compressive force in a rolling mill between two Teflon-coated steel sheets. The result is a strip of electrode about 180 mm long and about 0.09 mm thick. From this, electrode disks are blanked out using an arch punch or equivalent.
  • The OD outside diameter (OD) of the disks is 22 mm. They are dropped into a polypropylene gasket that has a 23 mm inner diameter (ID) and a 28 mm OD (see FIG. 42). This is then compressed in a vertical hydraulic press to 2000 pounds force, which compresses the lip downward and the electrode OD expands to fill the ID of the grommet. This is done for both the anode and cathode electrodes.
  • The 0.02 mm cellulose sheet is blanked into 22 mm disks and placed on a soaked paper towel. A second paper towel is placed over this and the flooded mass is allowed to sit for at least 16 hours. The paper toweling is to hold them under the distilled water.
  • When it is time to use the cellulose, it is tweezered out of the dish and placed on a dry paper towel and momentarily daubed to remove any standing water.

Cell Assembly:

The electrode grommets were 3D printed using PETG filament. FIG. 43 is a cross section of that part. The ID of the grommet is 25 mm and the OD of the disk is 22.25 mm. They are then compressed under 2000 pounds force between parallel plates, which expands the electrode in OD to compress within the grommet while reducing the thickness of that part as well. The result is a strong, uniform part that is easily assembled. The OD of the assembled part is 28 mm.

The cellulose separator is blanked at 27 mm, so totally covers the active electrode and is easily placed over the electrode-grommet assembly.

All housing components are 3D printed using PETG filament, but any filament that is water stable would work.

FIG. 47 depicts the anoxic cell in exploded view where 470 depicts the chamber that holds degassed water. It is covered by one or two layers of porous Teflon (471) film of the type used in air electrodes for metal air batteries. It is a full diameter disk to keep the liquid water from reaching the cell, while allowing 100% RH exposure to the cell. Number 472 depicts a fine nickel cloth cathode current collector. Number 473 depicts a soft, closed-pore neoprene gasket to prevent atmospheric oxygen from reaching the cell. Number 474 depicts the cell. This is in three layers as described above with the cathode assembly down, the hydrated cellulose separator next and the anode assembly on top in this view. Number 475 depicts the anode current collector. This is preferably a non-reactive metal such as gold-plated brass, nickel or other metals. Number 476 depicts the anode cover, which is simply a disk with a small indent (not shown) to house the anode current collector.

FIG. 48 depicts the anoxic cell in semi-compressed view where 480 depicts the chamber that holds degassed water. It is covered by one or two layers of porous Teflon (481) film of the type used in air electrodes for metal air batteries. It is a full diameter disk to keep the liquid water from reaching the cell, while allowing 100% RH exposure to the cell. Number 482 depicts a fine nickel cloth cathode current collector. Number 483 depicts a soft, closed-pore neoprene gasket to prevent atmospheric oxygen from reaching the cell. Number 484 depicts the cell. This is in three layers as described above with the cathode assembly down, the hydrated cellulose separator next and the anode assembly on top in this view. Number 485 depicts the anode current collector. This is preferably an electrically conductive and non-reactive metal such as gold-plated brass, nickel or other metals. Number 486 depicts the anode cover, which is simply a disk with a small indent (not shown) to house the anode current collector.

Preferably, a conductive paint is applied on the external surface of the electrodes to reduce internal resistance. This Example used a water-based spray paint, but a 50% dilution of the paint used to coat the inside of alkaline cells would work as well, for example. This improved internal impedance and current output.

The Teflon binder is hydrophobic, and alternative hydrophobic binders may be used. There are many such hydrophobic additives that are used in the battery industry and some non-limiting examples include: PVDF (Polyvinylidene Fluoride), Modified SBR (Styrene Butadiene Copolymer) from Targray, FEP (fluoroplastic powder), paraffins, epoxies, and other similar materials.

Energy harvesters have been described herein as devices that do not store energy, but rather gather it from the environment. Although in this embodiment the cavity in which the electrodes are house is excluded from the surrounding environment during operation of the device, we hereby still refer to this embodiment as an energy harvester.

In this embodiment a cellulosic separator was used as it is well suited for the requirement of being hydrophilic, and wettable, but alternative separators can be used which are not SSE's or include metal oxides. Such nonlimiting alternatives include: polyolefins such as Setela and Celgard, glass fiber separators, and separators including polyester and nylon.

Mechanism: That the cell in this Example runs without atmospheric oxygen is surprising when considering the mechanism discussed above. Without being bound by theory, we believe the mechanism of producing electricity in this embodiment proceeds as follows:

Cathode Mechanism:

The Cathode combines protons (H⁺), electrons (e⁻) and oxygen (O₂), producing H₂O and H₂.

WO_2.9 Mechanism

$\left(W^{+6}-V^o-W^{+6}\right)+H_2{O}_v<-->\left(W^{+5}-O-W^{+5}\right)+$ $2H^{+}<-->{\left(W^{+5}-V^o-W^{+5}\right)}^{=}1/2O_2+2H^{+}+2e^{-}$ $\left(W^{+6}-V^o-W^{+6}\right)+H_2{O}_v<-->\left(W^{+5}-O-W^{+5}\right)+$ $2H^{+}<-->\left(W^{+5}-V^o-W^{+5}\right)1/2O_2+2H^{+}+\left(2e^{-}+2H^{+}\right)-->$ $\left(W^{+5}-V^o-W^{+5}\right)+1/2O_2+2H^{+}+2e^{-}<-->{\left(W^{+6}-O-W^{+6}\right)}^{=}+$ $2H^{+}<-->\left(W^{+6}-V^o-W^{+6}\right)+H_{2}O$

Or simplified:

$1/2O_2+2H^{+}+2e^{-}<\stackrel{\mathrm{WOx}}{--}>H_{2}O$

where the ½O₂ is derived from water vapor, catalyzed by the tungsten sub-oxide.

Co3O4 mechanism: (Does NOT require external oxygen, only H⁺ and e⁻)

$2{\mathrm{Co}}_3{O}_4+2H^{+}+2e^{-}-->2{\mathrm{Co}}_3{\mathrm{Co}}_4+H_2$

Or simplified:

$2H^{+}+2e^{-}\stackrel{\mathrm{CoOx}}{--}>H_2$

Mechanism for the Co₃O₄ catalysis of water re-combination:

${\mathrm{Co}}_3{O}_{4}V+H_{2}O+2H^{+}+2e^{-}-->{\mathrm{Co}}_3{O}_{4}O+1/2H_2+3H^{+}{\mathrm{Co}}_3{O}_{4}O+1/2H_2+3H^{+}-->{\mathrm{Co}}_3{O}_{4}V+H_{2}O+H_2$

Or expanded:

Co₃O₄ is valence +4 cobalt and a cobalt +3 with four resident oxygens (Co⁺⁴Co⁺³O₄) and a vacancy (or two).

$\left({\mathrm{Co}}^{+3}-V^o-{\mathrm{Co}}^{+3}\right)+H_{2}O-->\left({\mathrm{Co}}^{+4}-O-{\mathrm{Co}}^{+4}\right)+2H^{+}+2e^{-}$

Co₃O₄ and WO_2.9 electron transfer in conduction bands

$2\left(W^{+5}-V^o-W^{+5}\right)+2\left({\mathrm{Co}}^{+4}-V^o-{\mathrm{Co}}^{+4}\right)+4e^{-}\to 2\left(W^{+6}-V^o-W^{+6}\right)+2\left({\mathrm{Co}}^{+3}-V^o-{\mathrm{Co}}^{+3}\right)\left(W^{+6}-V^o-W^{+6}\right)+H_{2}O-->\left(W^{+5}-O-W^{+5}\right)+H_2\left({\mathrm{Co}}^{+3}-V^o-{\mathrm{Co}}^{+3}\right)+H_{2}O-->\left({\mathrm{Co}}^{+4}-O-{\mathrm{Co}}^{+4}\right)+H_2$

Anode Mechanism:

The anode splits water using TiO_x and WO_x as catalyst, consuming H₂O and liberating protons (H⁺), electrons (e⁻) and O₂.

Tungsten Set

$\left(W^{+6}-V^o-W^{+6}\right)+H_{2}O-->\left(W^{+5}-O-W^{+5}\right)+2H^{+}\left(W^{+5}-O-W^{+5}\right)-->\left(W^{+5}-V^o-W^{+5}\right)+1/2O_2+2e^{-}\mathrm{Or}\mathrm{simplified}:H_{2}O<\stackrel{\mathrm{WOx}}{--}>1/2O_2+2H^{+}+2e^{-}$

Titanium Set

$\mathrm{In}\mathrm{general}:H_{2}O+{\mathrm{TiO}}_x-->{\mathrm{TiO}}_x{\mathrm{OH}}^{-}+H^{+}-->{\mathrm{TiO}}_x+1/2O_2+H^{+}+2e^{-}$

In detail:

$\mathrm{Or}\mathrm{simplified}:H_{2}O\stackrel{\mathrm{TiOx}}{--}>1/2O_2+2H^{+}+2e^{-}\mathrm{Or}\mathrm{combined}\mathrm{to}:H_{2}O\stackrel{\mathrm{TiOx}\&\mathrm{WOx}}{--}>1/2O_2+2H^{+}+2e^{-}$

WO₃ and TiO₂ electron transfer in conduction bands:

$2\left(W^{+5}-V^o-W^{+5}\right)+2\left({\mathrm{Ti}}^{+4}-V^o-{\mathrm{Ti}}^{+4}\right)+4e^{-}\to 2\left(W^{+6}-V^o-W^{+6}\right)+2\left({\mathrm{Ti}}^{+3}-V^o-{\mathrm{Ti}}^{+3}\right)$

The definitions for the Kroger-Vink Notation used herein and be found at many sources including Wikipedia (en.wikipedia.org/wiki/Kröger-Vink_notation) or more scholarly sites such as (www.tf.uni-kiel.de/matwis/amat/def_en/kap_2/backbone/r2_4_2.html).

References cited in this disclosure are incorporated herewith by reference in their entirety.

While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.

Claims

1. A solid-state energy harvester, comprising: a) an anode comprising a first transition metal suboxide;b) a cathode comprising a second transition metal suboxide; andc) a separator interposed between the anode and the cathode;wherein at least one of the anode, the cathode or the separator comprises water; andwherein the harvester produces electricity when electrically connected to an external load.

2. The solid-state energy harvester of claim 1, wherein the first transition metal suboxide and the second transition metal suboxide are the same.

3. The solid-state energy harvester of claim 1, wherein the first transition metal suboxide and the second transition metal suboxide are different.

4. The solid-state energy harvester of claim 1, wherein the anode further comprises a transition metal suboxide different from the first transition metal suboxide.

5. The solid-state energy harvester of claim 1, wherein the cathode further comprises a transition metal suboxide different from the second transition metal suboxide.

6. The solid-state energy harvester of claim 1, wherein the separator is hydrophilic.

7. The solid-state energy harvester of claim 1, wherein the separator does not substantially comprise a metal oxide.

8. The solid-state energy harvester of claim 1, wherein the separator conducts protons and is electrically resistive.

9. The solid-state energy harvester of claim 1, wherein the separator comprises water.

10. The solid-state energy harvester of claim 1, wherein the anode further comprises an electrically conductive additive.

11. The solid-state energy harvester of claim 1, wherein the cathode further comprises an electrically conductive additive.

12. The solid-state energy harvester of claim 1, wherein the anode further comprises a hydrophobic additive.

13. The solid-state energy harvester of claim 1, wherein the cathode further comprises a hydrophobic binder.

14. The solid-state energy harvester of claim 1, wherein at least one of the transition metal suboxides comprises tungsten.

15. The solid-state energy harvester of claim 1, wherein at least one of the transition metal suboxides comprises titanium.

16. The solid-state energy harvester of claim 1, wherein at least one of the transition metal suboxides comprises cobalt.

17. The solid-state energy harvester of claim 1, wherein the anode and cathode are both planar shaped.

18. The solid-state energy harvester of claim 1, wherein the anode and cathode are positioned in parallel relative each other.

19. The solid-state energy harvester of claim 1, further comprising a housing having a cavity within, wherein the anode and cathode are positioned in the cavity.

20. The solid-state energy harvester of claim 19, wherein the housing excludes ambiance from the cavity.

21. The solid-state energy harvester of claim 19, wherein the housing allows ambiance to reach the cathode.

22. The solid-state energy harvester of claim 1, further comprising multiple anode and cathode electrode couples each generating electricity, wherein all such electrodes are housed within the cavity.

23. A solid-state energy harvester system, comprising a first energy harvester and a second energy harvester, wherein the first energy harvester and the second energy harvester comprise the solid-state harvester of claim 1, and wherein the first energy harvester is in electrical connection with the second energy harvester.

24. A solid-state energy harvester system of claim 23, further comprising a storage battery, wherein the first energy harvester and the second energy harvester generate electrons which are stored in the storage battery.

25. A method of producing electricity including a solid-state energy harvester, comprising: a) preparing an anode mixture comprising a first transition metal suboxide, and a binder;b) preparing a cathode mixture comprising a second transition metal suboxide, and a binder;c) forming the anode mixture into a first layer, and forming the cathode mixture into a second layer;d) positioning the first layer and second layer on opposing sides of a separator; ande) electrically connecting the first layer to the second layer via an external electrical connection while the first layer and the second layer are exposed to humidity, whereby the energy harvester produces electricity.

26. The method of claim 25, wherein the preparing an anode mixture step a) further comprises a first metal suboxide different from the first transition metal suboxide.

27. The method of claim 26, wherein in the preparing a cathode mixture step b) further comprises a second metal suboxide different from the second transition metal suboxide.

28. The method of claim 25, wherein in both preparing steps a) and b), an electrically conductive additive is added to both the anode and cathode mixtures.

29. The method of claim 25, wherein in both preparing steps a) and b), a hydrophobic additive is added to both the anode and cathode mixtures.

30. The method of claim 25, further comprising a wetting step in which the separator is wetted with water.