Stacked Dual Cathode Device

Abstract

This disclosure provides systems, methods, and apparatus related to a stacked dual cathode device. In one aspect, a device includes an anode chamber and a cathode chamber. The anode chamber includes an anode layer. The cathode chamber includes a first cathode layer and a second cathode layer. The device further includes an ion exchange membrane. The anode layer is in contact with a first side of the ion exchange membrane. A first side of the first cathode layer is in contact with a second side of the ion exchange membrane. The cathode chamber further includes a conductive membrane. A first side of the conductive membrane is in contact with a second side of the first cathode layer and a second side of the conductive membrane is in contact with a first side of the second cathode layer.

Description

TECHNICAL FIELD

This disclosure relates generally to a stacked dual cathode device and more particularly to a stacked dual cathode device for electrochemical CO₂ reduction.

BACKGROUND

Electrochemical reduction of carbon dioxide into valuable chemicals and fuels represents a promising path towards combating increasing CO₂ concentrations in the atmosphere. However, reduction of CO₂ into molecules containing more than one carbon atom is currently difficult to achieve at high selectivities using a single cathodic electrode.

Dual cathodes comprise at least two different catalytically-active surfaces. Traditionally, these catalytically-active surfaces are placed next to each other, limiting the control over the tandem reactions.

SUMMARY

Described herein is a stacked dual cathode that is integrated into an electrochemical device. The electrochemical device can be used to reduce CO₂.

The stacked dual cathode device described herein comprises a first cathode layer which is in contact with an ion exchange membrane that separates the cathode from the anode. The first cathode layer achieves the conversion of carbon dioxide (CO₂) (or some other compound) to carbon monoxide (CO) (or another intermediate product). The carbon monoxide is then converted, for example, to ethylene, on a second cathode layer. The second cathode layer is separated from the first cathode layer by a conductive membrane that is both electronically and ionically conductive, but impedes or prevents undesired gas crossover between the first cathode layer and the second cathode layer.

The conductive membrane comprises either anion-exchange or cation-exchange materials combined with a PEDOT:PSS polymer (or some other electrically conductive polymer). In some embodiments, the conductive membrane can be spray-coated into layers of variable thickness. The conductive membrane enables the incorporation of a wide range of electrochemical tandem reactions. The approach described herein serves as a potential answer to the challenge of reducing CO₂ into molecules containing more than one carbon atom at high selectivities and single-pass conversion ratios.

Details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a schematic illustration of a stacked dual cathode device.

FIG. 2 shows an example of an exploded schematic illustration of a stacked dual cathode device.

DETAILED DESCRIPTION

Reference will now be made in detail to some specific examples of the invention including the best modes contemplated by the inventors for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise.

The terms “about” or “approximate” and the like are synonymous and are used to indicate that the value modified by the term has an understood range associated with it, where the range can be ±20%, ±15%, ±10%, ±5%, or ±1%. The terms “substantially” and the like are used to indicate that a value is close to a targeted value, where close can mean, for example, the value is within 80% of the targeted value, within 85% of the targeted value, within 90% of the targeted value, within 95% of the targeted value, or within 99% of the targeted value.

While there have been some reports of sequential electrochemical devices, the device described herein does not rely on free diffusion of intermediate products from a first cathode layer to a second cathode layer. Instead, with the device described herein, the reactants flow in a controlled way through the first cathode layer before flowing through the second cathode layer. This allows the first reaction to proceed to completion before the second reaction is initiated.

As the cathode layers are stacked on top of each other, the catalytic area for each cathode layer can equal the device footprint. This compares favorably to traditional tandem devices which employ coplanar cathodic surfaces, meaning the allowed area for each cathode catalyst is substantially less than the total device area. This carries implications for improving product conversion efficiencies relative to conventional tandem architectures.

Further, the device described herein allows for a stacked dual cathode assembly in a membrane electrode assembly-type cell format, which generally gives higher performance by reducing ionic path lengths relative to alternative designs.

FIG. 1 shows an example of a schematic illustration of a stacked dual cathode device. FIG. 2 shows an example of an exploded schematic illustration of a stacked dual cathode device. The device 100 includes an anode chamber 105, a cathode chamber 155, and an ion exchange membrane 190. The ion exchange membrane 190 is disposed between the anode chamber 105 and the cathode chamber 155.

The anode chamber 105 includes an anode layer 110 that includes an anode catalyst (not shown). The device 100 further includes a first anode port 115 and a second anode port 120. The first anode port 115 is operable to admit an oxidation reactant and a second anode port 120 is operable to exhaust oxygen or some other oxidized reactant.

The cathode chamber 155 includes a first cathode layer 160 and a second cathode layer 180. The first cathode 160 layer includes a first cathode catalyst (not shown) and the second cathode layer 180 includes a second cathode catalyst (now shown). The device 100 further including a first cathode port 165 and a second cathode port 170. The first cathode port 165 is operable to admit a reduction reactant and the second cathode port 170 is operable to exhaust a final product.

In some embodiments, the first cathode port 165 is on the anode side of the device 100 (as shown in FIG. 1) and enables an entry point of reduction reactant towards the first cathode layer 160. A conventional configuration with both cathode ports on the cathode side of the device may be difficult to achieve because the cathode layers are thin.

The ion exchange membrane 190 is disposed between the anode chamber 105 and the cathode chamber 155. The ion exchange membrane 190 separates the anode chamber 105 and the cathode chamber 155. The ion exchange membrane 190 is operable to conduct ions. The anode layer 110 is in contact with a first side of the ion exchange membrane 190. A first side of the first cathode layer 160 is in contact with a second side of the ion exchange membrane 190.

The cathode chamber 155 further includes a conductive membrane 185. The conductive membrane 185 is operable to conduct electrons and to conduct ions. Ion exchange membranes are typically insulating materials, prohibiting electronic conduction. By adding an electrically conducting polymer (e.g., PEDOT:PSS) to the polymer mixture for an ion exchange membrane and using appropriate conditions for a spray coating process, a membrane having both electrical and ionic conductivity can be fabricated. A first side of the conductive membrane 185 is in contact with a second side of the first cathode layer 160 and a second side of the conductive membrane 185 is in contact with a first side of the second cathode layer 180.

When the device 100 is in operation, a reduction reactant flows through the first cathode layer 160 where it is reduced to a first reduction product. The first reduction product flows to an open volume 175 on an edge of the first cathode layer 160, the conductive membrane 185, and the second cathode layer 180. The first reduction product then flows through the second cathode layer 180 where it is reduced to the final product.

In some embodiments, an entire first surface of the first cathode layer 160 is in contact with the ion exchange membrane 190. In some embodiments, an entire second surface of the first cathode layer 160 is in contact with the conductive membrane 185. In some embodiments, an entire first surface of the second cathode layer 180 is in contact with the conductive membrane 185. In some embodiments, an entire second surface of the second cathode layer 180 is in contact with a surface of the device 100 (e.g., a cathode endplate 152).

In some embodiments, the device 100 further includes an anode endplate 102 and a cathode endplate 152. In some embodiments, the anode endplate 102 and the cathode endplate 152 comprise a plastic (e.g., PMMA) or a metal. In some embodiments, the device 100 further includes an anode gasket 104 and a cathode gasket 154. In some embodiments, the anode gasket 104 is disposed between the anode endplate 102 and the ion exchange membrane 190, surrounding the anode layer 110 and leaving space for the first cathode port 165. In some embodiments, the cathode gasket 154 is disposed between the cathode endplate 152 and the ion exchange membrane 190, surrounding the second cathode layer 180, the conductive membrane 185, and the first cathode layer 160. In some embodiments, the cathode gasket 154 comprises multiple layers of gasket material to facilitate device assembly. The anode gasket material and the cathode gasket material is chemically compatible with chemicals flowing through the device. In some embodiments, the anode gasket material and the cathode gasket material are a material from a group silicone, polytetrafluoroethylene, ethylene tetrafluoroethylene, and perfluoroelastomer.

In some embodiments, the first cathode port 165 includes a port in the ion exchange membrane 190. In some embodiments, an entire first surface of the first cathode layer 160 (except for an area of the port in the ion exchange membrane 190) is in contact with the ion exchange membrane 190. In some embodiments, an entire second surface of the first cathode layer 160 is in contact with the conductive membrane 185. In some embodiments, an entire first surface of the second cathode layer 180 is in contact with the conductive membrane 185. In some embodiments, an entire second surface of the second cathode layer 180 (except for an area of the second cathode port 170) is in contact with a surface of the device.

In some embodiments, the ion exchange membrane 190 is a membrane from a group a cation exchange membrane (e.g., a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (e.g., Nafion, The Chemours Company, Wilmington, DE), an anion exchange membrane (e.g., Sustainion, Dioxide Materials, Boca Raton, FL), Fumion (Fumatech, Bietigheim-Bissingen, Germany), Selemion (Bellex International Corporation, Wilmington, DE), etc.), and a bipolar membrane.

In some embodiments, the conductive membrane 185 comprises a mixture of an ion exchange polymer and a conductive polymer. In some embodiments, the ion exchange polymer comprises a polymer from a group a cation exchange polymer and an anion exchange polymer. In some embodiments, the conductive polymer comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and the ion exchange polymer comprises a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer. In some embodiments, the conductive polymer comprises polyaniline (PANI), and the ion exchange polymer comprises an anion exchange polymer (e.g., Sustainion). In some embodiments, a weight ratio of the conductive polymer to the ion exchange polymer is about 1:3 to 3:1. In some embodiments, the conductive membrane 185 is about 10 microns to 100 microns thick, about 15 microns to 45 microns thick, or about 30 microns thick.

The ratio between conductive polymer and ion exchange polymer in the conductive membrane 185 can be adjusted to achieve specified properties for ionic and electronic conduction. Further, the thickness of the conductive membrane 185 can be adjusted to achieve a specified voltage drop across the conductive membrane 185. Different voltage drops across the conductive membrane 185 are expected to yield different product distributions in the first cathode layer 160 or the second cathode layer 180. Further, the concept of the structure of the device 100 (i.e., the dual stacked cathodes) is not limited to two tandem reactions, but can in principle be extended to multi-step reactions (e.g., using a tri-stacked cathode).

In some embodiments, the first cathode layer 160 comprises a porous material with the first cathode catalyst disposed thereon. In some embodiments, the second cathode layer 180 comprises a porous material with the second cathode catalyst disposed thereon. In some embodiments, the first cathode layer 160 and the second cathode layer 180 are each a layer from a group carbon cloth, carbon felt, carbon paper, a metal foam, and a metal mesh (e.g., a porous titanium mesh). In some embodiments, the first cathode layer 160 and the second cathode layer 180 are each about 50 microns to 450 microns thick, about 150 microns to 450 microns thick, or about 300 microns thick.

In some embodiments, the first cathode catalyst is disposed on the second side of the first cathode layer 160. In some embodiments, the second cathode catalyst is disposed on the first side of the second cathode layer 180. In some embodiments, the first cathode catalyst and the second cathode catalyst are each about 10 nanometers to 300 nanometers thick, about 50 nanometers to 150 nanometers thick, or about 100 nanometers thick. In some embodiments, the first cathode catalyst is disposed on the first side of the conductive membrane 185, and the second cathode catalyst is disposed on the second side of the conductive membrane 185. In this configuration, the cathode layers 160 and 180 are still included in the device 100 to provide channels for gas transport.

In some embodiments, the first cathode catalyst comprises silver or gold, the second cathode catalyst comprises copper, the reduction reactant comprises carbon dioxide (CO₂), the first product comprises carbon monoxide (CO), and the final product comprises ethylene (C₂H₄). In some embodiments, the first cathode catalyst comprises zinc, the second cathode catalyst comprises cobalt phthalocyanine (e.g., immobilized cobalt phthalocyanine), the reduction reactant comprises carbon dioxide (CO₂), the first product comprises carbon monoxide (CO), and the final product comprises methanol (CH₃OH). In some embodiments, the first cathode catalyst comprises MoS₂ or MoS_x, which also generate a first product comprising carbon monoxide (CO).

In some embodiments, a layer of a material comprising the ion exchange membrane 190 is disposed on the first side of the first cathode layer 160. In some embodiments, the first cathode layer 160 is ionically conductive. In some embodiments, the first cathode layer 160 is coated with an ion exchange material to provide ion conduction from the ion exchange membrane 190 to the conductive membrane 185.

In some embodiments, the anode layer 110 comprises a porous material with the anode catalyst disposed thereon. In some embodiments, the anode layer 110 is a layer from a group carbon cloth, carbon felt, carbon paper, a metal foam, and a metal mesh (e.g., a porous titanium mesh). In some embodiments, the anode layer 110 is about 50 microns to 450 microns thick, 150 microns to 450 microns thick, or about 300 microns thick.

In some embodiments, the anode catalyst comprises an oxygen evolution reaction catalyst. In some embodiments, the oxygen evolution reaction catalyst is a catalyst from a group iridium, ruthenium, a nickel-containing compound, an iron-containing compound, and a cobalt-containing compound. In some embodiments, the oxidation reaction is a hydrogen oxidation reaction or water oxidation to hydrogen peroxide reaction. In some embodiments, the anode catalyst is about 10 nanometers to 300 nanometers thick, about 50 nanometers to 150 nanometers thick, or about 100 nanometers thick.

In some embodiments, the anode layer 110 has a first side and a second side, with the anode catalyst disposed on the second side of the anode layer 110, and the second side of the anode layer 110 in in contact with the first side of the ion exchange membrane 190.

In some embodiments, the oxidation reactant comprises water. In some embodiments, the water includes potassium bicarbonate dissolved therein. The potassium bicarbonate acts as a pH buffer and reduces the ionic resistance across the entire device, relative to operation in pure water.

For example, describing the operation of the device 100 as a whole, CO₂ flows through the first cathode layer 160 and is electrochemically reduced to an intermediate product, such as CO. The flow of CO₂ and CO (after the conversion of the CO₂ to CO) passes through the entire first cathode layer 160 before it reaches the second cathode layer 180, as the conductive membrane 185 limits gas exchange between layers. It is possible to achieve a CO₂-free stream of CO reaching the second cathode layer 180.

At the second cathode layer 180, the intermediate product (e.g., CO) flows through the second cathode layer 180 and is further reduced to a product, such as ethylene. The conductive membrane 185 provides both ionic and electronic conduction, enabling electrochemical reactions at the second cathode layer 180. In the anode chamber 105 of the device 100, the oxidation reaction, typically water oxidation, completes the full cell reaction with hydrogen or hydroxide ions traveling through the ion exchange membrane 190. The required voltage for the reactions to occur is supplied by the electrical grid, a photovoltaic (PV) element (not shown), or other (renewable) electricity sources.

CONCLUSION

In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention.

Claims

1. A device comprising: an anode chamber, the anode chamber including an anode layer including an anode catalyst, the anode chamber further including a first anode port operable to admit an oxidation reactant and a second anode port operable to exhaust oxygen;a cathode chamber, the cathode chamber including a first cathode layer and a second cathode layer, the first cathode layer including a first cathode catalyst and the second cathode layer including a second cathode catalyst, the cathode chamber further including a first cathode port operable to admit a reduction reactant and a second cathode port operable to exhaust a final product; andan ion exchange membrane, the anode layer being in contact with a first side of the ion exchange membrane, and a first side of the first cathode layer being in contact with a second side of the ion exchange membrane; andthe cathode chamber further including a conductive membrane, the conductive membrane operable to conduct electrons and to conduct ions, a first side of the conductive membrane being in contact with a second side of the first cathode layer and a second side of the conductive membrane being in contact with a first side of the second cathode layer.

2. The device of claim 1, wherein when the device is in operation, the reduction reactant flows through the first cathode layer where it is reduced to a first reduction product, the first reduction product flows to an open volume on an edge of the first cathode layer, the conductive membrane, and the second cathode layer, and the first reduction product then flows through the second cathode layer where it is reduced to the final product.

3. The device of claim 1, wherein an entire first surface of the first cathode layer is in contact with the ion exchange membrane, wherein an entire second surface of the first cathode layer is in contact with the conductive membrane, wherein an entire first surface of the second cathode layer is in contact with the conductive membrane, and wherein an entire second surface of the second cathode layer is in contact with a surface of the device.

4. The device of claim 1, wherein the first cathode port includes a port in the ion exchange membrane, wherein an entire first surface of the first cathode layer except for an area of the port in the ion exchange membrane is in contact with the ion exchange membrane, wherein an entire second surface of the first cathode layer is in contact with the conductive membrane, wherein an entire first surface of the second cathode layer is in contact with the conductive membrane, and wherein an entire second surface of the second cathode layer except for an area of the second cathode port is in contact with a surface of the device.

5. The device of claim 1, wherein the first cathode port includes a port in the ion exchange membrane.

6. The device of claim 1, wherein the ion exchange membrane is a membrane from a group a cation exchange membrane, an anion exchange membrane, and a bipolar membrane.

7. The device of claim 1, wherein the conductive membrane comprises a mixture of an ion exchange polymer and a conductive polymer.

8. The device of claim 1, wherein the first cathode layer comprises a porous material with the first cathode catalyst disposed thereon.

9. The device of claim 1, wherein the second cathode layer comprises a porous material with the second cathode catalyst disposed thereon.

10. The device of claim 1, wherein the first cathode layer and the second cathode layer are each a layer from a group carbon cloth, carbon felt, carbon paper, a metal foam, and a metal mesh.

11. The device of claim 1, wherein the first cathode layer and the second cathode layer are each about 50 microns to 450 microns thick.

12. The device of claim 1, wherein the first cathode catalyst is disposed on the second side of the first cathode layer, and wherein the second cathode catalyst is disposed on the first side of the second cathode layer.

13. The device of claim 1, wherein a layer of a material comprising the ion exchange membrane is disposed on the first side of the first cathode layer.

14. The device of claim 1, wherein the anode layer comprises a porous material with the anode catalyst disposed thereon.

15. The device of claim 1, wherein the anode catalyst comprises an oxygen evolution reaction catalyst.

16. The device of claim 1, wherein the anode layer is about 50 microns to 450 microns thick.

17. The device of claim 1, wherein the anode layer is a layer from a group carbon cloth, carbon felt, carbon paper, a metal foam, and a metal mesh.

18. The device of claim 1, wherein the anode layer has a first side and a second side, wherein the anode catalyst is disposed on the second side of the anode layer, and wherein the second side of the anode layer is in in contact with the first side of the ion exchange membrane.

19. The device of claim 1, wherein the oxidation reactant comprises water.

20. The device of claim 1, wherein the first cathode catalyst comprises silver or gold, wherein the second cathode catalyst comprises copper, wherein the reduction reactant comprises carbon dioxide (CO2), wherein the first product comprises carbon monoxide (CO), and wherein the final product comprises ethylene (C2H4).