Patent Application
20240401210
The present disclosure relates to the synthesis of oxide and hydroxide nanomaterials of certain metals that are used in a variety of applications, for example to produce rechargeable battery compositions. In particular, the present disclosure relates to synthesis of transition metal hydroxides and oxides, and nanoparticles thereof.
Transition metal oxides and hydroxides have many important industrial applications, including as precursors for rechargeable battery cathode materials. However, conventional processes for synthesizing transition metal oxides and hydroxides generally produce large amounts of hazardous waste. Similarly, microparticles and nanoparticles that include iron are used in a variety of industrial processes. In particular, iron microparticles and nanoparticles may be preferred in applications in which a high specific surface area (e.g., meters2 (m2)/gram (g)) is desired.
However, conventional processes to produce nanoparticles of metals, for example iron, generally are energy intensive, time consuming, expensive and may still not produce particles that are sufficiently small or have a monodisperse particle size.
The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. It should be noted that references to “an” or “one” embodiment or aspect in this disclosure are not necessarily to the same embodiment or aspect, and they mean at least one. In the drawings:
In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding. One or more aspects may be practiced without these specific details. Features described in one embodiment or aspect of the disclosure may be combined with features described in a different embodiment. In some examples, well-known structures and devices are described with reference to a block diagram form in order to avoid unnecessarily obscuring the present invention.
Before describing several example aspects of the disclosed technology, it is to be understood that the technology is not limited to the details of construction or process steps set forth in the following description. The technology is capable of other implementations and of being practiced or being carried out in various ways.
One or more aspects include techniques by which transition metals may be oxidized at room temperature using an electrolyte and a porous carbon component. The porous carbon element may act as an “air cathode” that reduces oxygen, thereby causing oxygen to act as a cathode in an electrochemical cell with a transition metal anode. In this way, aspects described herein facilitate a room temperature redox reaction with transition metals. Some aspects described herein may oxidize transition metals that are resistant to corrosion, such as nickel. Aspects of the process described herein may react bulk transition metals (and/or their alloys) at room temperature with oxygen via a porous carbon component (or equivalently, porous carbon element) that reduces the activation energy needed for the reduction of oxygen. The transition metal reaction product(s) may be further processed into rechargeable battery cathode materials without also synthesizing hazardous waste products. In some examples, magnetic and/or non-magnetic nanoparticles of iron oxide are produced. In some examples, the iron oxide nanoparticles have high, and even unexpectedly high, specific surface area as measured in meters2 (m2)/gram (g)
For convenience of explanation, aspects that are related to active materials for a rechargeable battery, the term “cathode” is used to refer to a battery component that is oxidized during charging (e.g., Co3+ to Co4+) and is reduced during discharging (e.g., Co4+ to Co3+). The term “anode” is used to refer to a battery component that is reduced during charging (e.g., from C to LiC6) and is oxidized during discharging (e.g., from LiC6 to C). Furthermore, for brevity the term “transitional metal” also includes alloys, intermetallic compounds, and other combinations of multiple transition metals.
One or more aspects described in this Specification and/or recited in the claims may not be included in this General Overview section.
With respect to the terms used in this disclosure, the following definitions are provided. This application will use the following terms as defined below unless the context of the text in which the term appears requires a different meaning.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. The term “about” used throughout this specification is used to describe and account for small fluctuations. For example, the term “about” can refer to less than or equal to ±10%, or less than or equal to ±5%, such as less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.2%, less than or equal to ±0.1% or less than or equal to ±0.05%. All numeric values herein are modified by the term “about,” whether or not explicitly indicated. A value modified by the term “about” of course includes the specific value. For instance, “about 5.0” must include 5.0.
Within the context of the present disclosure, in some examples, the terms “framework” or “framework structure” refer to the network of interconnected oligomers, polymers, or colloidal particles that form the solid structure of a gel or an aerogel. The polymers or particles that make up the framework structures typically have a diameter of about 100 angstroms. In examples of pyrolyzed or carbonized aerogels, the terms “framework” or “framework structure” refer to the interconnected network of linear fibrils, that may be connected together at nodes to form a framework that defines pores.
As used herein, the terms “aerogel,” and “aerogel material” refer to a solid object, irrespective of shape or size, comprising a framework of interconnected solid structures, with a corresponding network of interconnected pores integrated within the framework, and containing gases such as air as a dispersed interstitial medium. As such, aerogels are open non-fluid colloidal or polymer networks that are expanded throughout their whole volume by a gas, and are formed by the removal of all swelling agents from a corresponding wet-gel without substantial volume reduction or network compaction. Aerogels are generally characterized by the following physical and structural properties (according to nitrogen porosimetry testing and helium pycnometry) attributable to aerogels: (a) an average pore diameter ranging from about 2 nm to about 100 nm; (b) a porosity of at least 60% or more, and (c) a specific surface area of about 1, about 10, or about 20, to about 100 or about 1000 m2/g by nitrogen sorption analysis. It can be understood that the inclusion of additives, such as a reinforcement material or an electrochemically active species, for example, silicon, may decrease porosity and the specific surface area of the resulting aerogel composite. Densification may also decrease porosity of the resulting aerogel composite. Aerogel materials of the present disclosure (e.g., polyimide and carbon aerogels) include any aerogels which satisfy the defining elements set forth in the previous paragraph.
Aerogel materials of the present disclosure thus include any aerogels or other open-celled compounds, which satisfy the defining elements set forth in previous paragraphs, including compounds, which can be otherwise categorized as xerogels, cryogels, ambigels, microporous materials (e.g., polymer foams), and the like.
As used herein, the term “xerogel” refers to a gel comprising an open, non-fluid colloidal or polymer networks that is formed by the removal of all swelling agents from a corresponding gel without any precautions taken to avoid substantial volume reduction or to retard compaction. A xerogel generally comprises a compact structure. Xerogels suffer substantial volume reduction during ambient pressure drying and generally have a porosity of about 40% or less.
In certain examples, the present disclosure involves the formation and use of nanoporous carbon-based scaffolds or structures, such as carbon aerogels, as electrode materials in an electrochemical cell to synthesize transition metal oxides, hydroxides, and nanoparticles thereof. Examples of porous carbon components of the present disclosure include, but are not limited to, carbonized aerogel materials (e.g., carbonized polyimide aerogel, carbonized polyamic acid aerogel) and carbonized polymer foams (e.g., carbonized polyurethane foam). For convenience, carbonized aerogels are sometimes equivalently referred to as “carbon aerogels” herein.
Furthermore, it is contemplated herein that the porous carbon materials, including carbon aerogels, can take the form of monolithic structures. The monolithic porous carbon has not need for a distinct binder material; in other words, the air cathode can be binder-less. As used herein, the term “monolithic” refers to porous carbon materials in which a majority (by weight) of the carbon included in the carbon material or composition is in the form of a unitary, continuous, interconnected carbon structure. In the specific example of carbonized aerogel materials, this may include an interconnected aerogel nanostructure. Monolithic aerogel materials include aerogel materials which are initially formed to have a unitary interconnected gel or aerogel nanostructure, but which can be subsequently cracked, fractured or segmented into non-unitary aerogel nanostructures.
Monolithic porous carbon materials are differentiated from particulate porous carbon materials. The term “particulate porous carbon material” refers to porous carbon materials in which a majority (by weight) of the carbon included in the carbon material is in the form of particulates, particles, granules, beads, or powders, which can be combined together (i.e., via a binder, such as a polymer binder) or compressed together but which lack an interconnected structure between individual particles. Collectively, materials of this form will be referred to as having a powder or particulate form (as opposed to a monolithic form). It should be noted that despite an individual particle of a powder having a unitary structure, the individual particle is not considered herein as a monolith.
Within the context of the present disclosure, the terms “binder-less” or “binder-free” (or derivatives thereof) refer to a material being substantially free of binders or adhesives to hold that material together. For example, a monolithic nanoporous carbon material is free of binder since its framework is formed as a unitary, continuous interconnected structure. Advantages of being binder-less include avoiding any effects of binders, such as on electrical conductivity and pore volume. On the other hand, aerogel particles require a binder to hold together to form a larger, functional material; such larger material is not contemplated herein to be a monolith. In addition, this “binder-free” terminology does not exclude all uses of binders. For example, a monolithic aerogel, according to the present disclosure, may be secured to another monolithic aerogel or a non-aerogel material by disposing a binder or adhesive onto a major surface of the aerogel material. In this way, the binder is used to create a laminate composite and provide electrical contact to a current collector, but the binder has no function to maintain the stability of the monolithic aerogel framework itself.
In some examples, a carbonized aerogel may be used as the porous carbon element in the systems and methods described herein. Carbonized aerogels may be formed by carbonizing some compositions of organic polymer aerogels. One example of a carbonizable organic polymer aerogel is that of polyimide. Other examples of porous carbon sources are identified below.
Methods of forming a polyimide gel or aerogel include those in which a polyimide gel is prepared in an organic solvent solution from condensation of a diamine and a tetracarboxylic acid dianhydride to form a polyamic acid and dehydration of the polyamic acid. See, for example, U.S. Pat. Nos. 7,071,287 and 7,074,880 to Rhine et al., and U.S. Patent Application Publication No. 2020/0269207 to Zafiropoulos, et al.
Production of an aerogel, according to certain aspects, includes the following steps: i) formation of a solution containing a gel precursor; ii) formation of a gel from the solution; and iii) extracting the solvent from the gel materials to obtain a dried aerogel material.
In one example, a polyimide aerogel is formed by combining at least one diamine and at least one dianhydride in a common polar aprotic solvent(s). Additional details regarding polyimide gel/aerogel formation can be found in U.S. Pat. Nos. 7,074,880 and 7,071,287 to Rhine et al.; U.S. Pat. No. 6,399,669 to Suzuki et al.; U.S. Pat. No. 9,745,198 to Leventis et al.; Leventis et al., Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP), Chem. Mater. 2011, 23, 8, 2250-2261, among others, each of which is incorporated herein by reference in its entirety.
Nanoporous carbons, such as carbon aerogels, according to the present disclosure, can be formed from any suitable organic precursor materials. Examples of such materials include, but are not limited to, RF (resorcinol-formaldehyde), PF (phenol-furfural), PI (polyimide), polyamides, polyoxyalkylene, polyurethane, polyacrylonitrile, cresol formaldehyde, polyisocyanate, polyvinyl alcohol dialdehyde, polyisocyanurates, various epoxide resins, chitosan, and combinations and derivatives thereof. In some examples, the carbon aerogel is formed from a pyrolyzed/carbonized polyimide-based aerogel, i.e., the polymerization of polyimide. Even more specifically, the polyimide-based aerogel can be produced using one or more methodologies described in U.S. Pat. Nos. 7,071,287 and 7,074,880 to Rhine et al., e.g., by imidization of poly(amic) acid and drying the resulting gel using a supercritical fluid.
Carbonized aerogels of the present disclosure, e.g., polyimide-derived carbon aerogels, can have a residual “hetero-atom” (i.e., non-carbon atom) nitrogen content of at least about 1 wt % as determined by elemental analysis. For example, carbon aerogels can have a residual nitrogen content of at least about 1 wt %, and up to about 10 wt %. In some aspects, the residual nitrogen content is about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10 wt %.
In examples of the present disclosure, a dried polymeric aerogel composition can be subjected to a treatment temperature of 200° C. or above, 400° C. or above, 600° C. or above, 800° C. or above, 1000° C. or above, 1200° C. or above, 1400° C. or above, 1600° C. or above, 1800° C. or above, 2000° C. or above, 2200° C. or above, 2400° C. or above, 2600° C. or above, 2800° C. or above, or in a range between any two of these values, for carbonization of the organic (e.g., polyimide) aerogel. In some examples, the material is carbonized in the absence of oxygen and/or in a reducing environment. Exposure to this temperature can convert the dried polymeric aerogel into a carbonized aerogel. In exemplary aspects, a dried polymeric aerogel composition can be subjected to a treatment temperature in the range of about 1000° C. to about 1100° C., e.g., at about 1050° C. Without being bound by theory, it is contemplated herein that the electrical conductivity of the aerogel composition increases with carbonization temperature. In some examples, some compositions or types of aerogels will become conductive when carbonized above a threshold carbonization temperature (e.g., above 400° C., above 500° C., above 600° C.).
In some examples, carbonized aerogels, such carbonized polyimide aerogels and carbonized poly(amic) acid aerogels can be mechanically strong, exhibiting a Young's Modulus that is unexpectedly high for carbonized materials. In certain aspects, carbonized aerogel materials or compositions of the present disclosure have a Young's modulus of about 0.2 GPa or more, 0.4 GPa or more, 0.6 GPa or more, 1 GPa or more, 2 GPa or more, 4 GPa or more, 6 GPa or more, 8 GPa or more, or in a range between any two of these values. Young's modulus may be determined by methods known in the art, for example including, but not limited to: Standard Test Practice for Instrumented Indentation Testing (ASTM E2546, ASTM International, West Conshocken, PA); or Standardized Nanoindentation (ISO 14577, International Organization for Standardization, Switzerland). Within the context of the present disclosure, measurements of Young's modulus are acquired according to ASTM E2546 and ISO 14577, unless otherwise stated.
Within the context of the present disclosure, the term “pore size distribution” refers to the statistical distribution or relative amount of each pore size within a sample volume of a porous material. A narrower pore size distribution refers to a relatively large proportion of pores at a narrow range of pore sizes, thus enhancing the amount of pores that can surround the electrochemically active species and maximizing use of the pore volume. Conversely, a broader pore size distribution refers to relatively small proportion of pores at a narrow range of pore sizes. As such, pore size distribution can be measured as a function of pore volume and recorded as a unit size of a full width at half max of a predominant peak in a pore size distribution chart. The pore size distribution of a porous material may be determined by methods known in the art, for example including, but not limited to, surface area and porosity analyzer by nitrogen adsorption and desorption from which pore size distribution can be calculated. Within the context of the present disclosure, measurements of pore size distribution are acquired according to this method, unless otherwise stated. In some examples, aerogel materials or compositions of the present disclosure have a relatively narrow pore size distribution (full width at half max) of about 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 5 nm or less, or in a range between any two of these values.
Within the context of the present disclosure, the term “pore volume” refers to the total volume of pores within a sample of porous material. Pore volume is specifically measured as the volume of void space within the porous material, where that void space may be measurable and/or may be accessible by another material, for example an electrochemically active species such as silicon particles. It can be recorded as cubic centimeters per gram (cm3/g or cc/g). The pore volume of a porous material may be determined by methods known in the art, for example including, but not limited to, surface area and porosity analyzer by nitrogen adsorption and desorption from which pore volume can be calculated. Within the context of the present disclosure, measurements of pore volume are acquired according to this method, unless otherwise stated. In certain examples, aerogel materials or compositions of the present disclosure (including carbonized aerogels) have a relatively large pore volume of about 0.5 cc/g or more, 1 cc/g or more, 1.5 cc/g or more, 2 cc/g or more, 2.5 cc/g or more, 3 cc/g or more, 3.5 cc/g or more, 4 cc/g or more, or in a range between any two of these values.
Within the context of the present disclosure, the term “porosity” refers to empty space within an aerogel sample as a fraction of the total (envelope) volume of the aerogel sample. Porosity may be calculated by methods known in the art, for example including, but not limited to, skeletal density minus bulk density divided by the skeletal density. Skeletal density may be measured by helium pycnometry, among other methods. Bulk density may be determined by a ratio of weight to geometric volume of an aerogel sample. Within the context of the present disclosure, measurements of porosity are acquired according to this method, unless otherwise stated. In certain aspects, aerogel materials or compositions of the present disclosure have a porosity of about 99% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or in a range between any two of these values.
Within the context of the present disclosure, the term “pore size at max peak from distribution” refers to the value at the discernible peak on a graph illustrating pore size distribution. Pore size at max peak from distribution is specifically measured as the pore size at which the greatest percentage of pores is formed. It can be recorded as any unit length of pore size, for example m or nm. The pore size at max peak from distribution may be determined by methods known in the art, for example including, but not limited to, surface area and porosity analyzer by nitrogen adsorption and desorption from which pore size distribution can be calculated and pore size at max peak can be determined. Within the context of the present disclosure, measurements of pore size at max peak from distribution are acquired according to this method, unless otherwise stated. Aerogel materials or compositions of the present disclosure can have a pore size at max peak from distribution of about 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, 10 nm or less, 5 nm or less, 2 nm or less, or in a range between any two of these values.
Porous carbons of the present disclosure are not limited to carbonized aerogels. Other porous carbons that exhibit sufficient chemical activity to reduce oxygen in the systems described herein may also be used. In some examples, conventional polymer foams may be carbonized and used in any of the examples described herein. In one experimental example, a carbonized polyurethane foam was used to generate nickel hydroxide. In another example, a carbonized polyurethane foam was used to synthesize nanoparticles of iron oxide. It will be appreciated that other polymers that lend themselves to carbonization (e.g., those containing backbones with phenyl rings, unsaturated bonds, and other similar structures) may be foamed or synthesized to have a porous structure, and may subsequently be used in the systems and examples described herein. The carbonization techniques described above in Section 3.1 are applicable to carbonizing non-aerogel materials, namely heating the polymer to a carbonization temperature in the absence of oxygen.
Many common types of rechargeable batteries, such as lithium-ion batteries (“LIB”), use transition metal oxides and/or hydroxides as precursors to rechargeable battery cathode materials. Early generations of rechargeable LIB cathode materials relied on cobalt (Co) as the predominant transition metal. However, successive generations of rechargeable batteries have progressively reduced the amount of cobalt in cathode materials. For example, many early rechargeable battery compositions used cobalt exclusively as the multivalent transition metal in the cathode composition (e.g., lithium cobalt oxide (LiCoO2)). However, more recent compositions of cathode materials have replaced some cobalt with nickel and other substituents. Examples of cathode compositions that include both nickel and cobalt include, but are not limited to, LiNi1/3Co1/3Mn1/3O2 (“NCM 111”) and LiNi0.8Co0.1Mn0.1O2 (“NCM 811”).
Replacing cobalt with other transition metals has a number of benefits. For example, cobalt is known to be environmentally toxic and also known to pose various threats to human health. Replacing cobalt with other materials that are less toxic and/or pose less risk to health may reduce environmental and health risks associated with the production, use, and disposal of rechargeable batteries. In some examples, replacing cobalt with other materials may also reduce the cost of rechargeable batteries (e.g., on a per unit of stored energy basis, on a per charge/discharge cycle basis). Furthermore, replacing cobalt with other transition metals has additional benefits. Cobalt generally has a financial higher cost that other transition metals and may be mined under socially problematic situations. Using an alternative to cobalt may address these disadvantages.
Precursor materials to nickel, cobalt, and manganese (“NCM”) cathode compositions are generally formed via aqueous synthesis techniques that produce large amounts of wastewater. In some examples, transition metal salts, such as sulfates, are first reacted with potassium hydroxide (KOH) to produce water-insoluble metal hydroxides. These metal hydroxides include, in some examples, Ni(OH)2 among other transition metal oxides and/or hydroxides. The metal hydroxides are ultimately precipitated from solution into a solid form. These precipitates are washed with deionized water to remove potassium sulfate impurities and then dried. The dried precipitates are then combined with lithium carbonate (Li2CO3), and thermally processed to produce a cathode composition (e.g., NCM 111, NCM 811). In some examples, lithium hydroxide is used instead of lithium carbonate for high Ni content cathode materials.
The synthesis of nickel-based transition metal cathode materials has various drawbacks. For example, ammonia (NH3) is often added to aqueous transition metal solutions, such as those described above. While not wishing to be bound by theory, it is believed that ammonia forms complexes with transition metals in aqueous solution. These complexes are believed to stabilize the transition metal cations in the solution at high pH before a controlled precipitation with hydroxy anions (e.g., OH−) happens. This in turn may improve the compositional uniformity of the transition metal precipitates, ultimately improving the compositional uniformity of cathode compositions derived therefrom.
The waste products from the ammonia-containing aqueous solution present hazards to the environment and to human health. For example, these waste products may include NH3 and K2SO4. Both of these waste products require proper handling during processing, remediation, and treatment prior to disposal, all of which increase battery production costs and present environmental disadvantages. Furthermore, the aqueous processes described above are voluminous. Tens or hundreds of liters of waste product may be produced for every 1 kilogram of cathode composition. This large volume of waste product is a significant drawback, particularly given the potential scale of rechargeable battery production when applied to automotive and/or grid power storage applications. An alternative synthesis technique that produces stoichiometrically preferred cathode composition precursors without generating an abundance of hazardous waste would reduce production costs and reduce environmental and human health risks.
Furthermore, aspects described herein also beneficially eliminate the production of waste products used to synthesize the precursors to traditional NCM battery cathode material reaction. For example, nickel sulfate (NiSO4) used in the aqueous reaction described above may be synthesized by treating metallic nickel, or its hydroxide or carbonate salts, with sulfuric acid. The reaction product NiSO4 is separated, washed, and dried, all of which require energy and produce pollutants (e.g., sulfuric acid).
Surprisingly, it has been experimentally observed that certain types of porous carbon materials (including carbon aerogels produced according to techniques described above) may act as an “air cathode” to catalytically reduce oxygen at room temperature. When arranged in an electrochemical cell with aqueous electrolytes, oxygen can be reduced into hydroxide anions that can oxidize a transition metal counter-electrode. The techniques described herein may operate effectively even on transition metals normally resistant to oxidation. In some examples, aspects herein may oxidize nickel to produce nickel hydroxide. In some examples, aspects herein may react transition metal components to completion (i.e., completely consume the portions of transition metal in contact with an electrolyte) within a few hours and a room temperature.
The catalytic effect of carbon aerogels and other porous carbons described herein may be used to oxidize nickel in the solid state at room temperature (e.g., from 5° C. to 25° C.). This is unexpected given the kinetic unfavourability of oxidizing nickel beyond its naturally occurring passivation layer and reductive dissociation of the dioxygen into hydroxide. In some examples, aspects described herein may be used to synthesize precursor materials used in rechargeable batteries that include, but are not limited to, NCM111, NCM811, LiNi0.8Co0.15Al0.05O2 (“NCA 85 15 5”), among others.
While not wishing to be bound by theory, it is believed that the porous carbon element 104 may reduce the activation energy for the reduction of oxygen, as described above, thereby enabling the electrically connected transition metal to participate in a room temperature redox reaction. As also described above, room temperature oxidation of transition metals like those used in rechargeable battery cathode materials is unexpected and also has many benefits.
In various aspects, the porous carbon element 104 may be synthesized and/or produced according to the techniques described above. Some aspects of these techniques include pyrolysis of a polyimide-derived carbon aerogel. In some examples, the pyrolyzed polyimide derived carbon aerogel may include residual nitrogen or other heteroatoms (i.e., non-carbon atoms) that are not removed during aerogel synthesis or pyrolysis. Using the porous carbon element 104 as a catalyst to oxidize the transition metal electrode 116 may generate cathode precursor materials that include, but are not limited to nickel oxide (NiO), nickel hydroxide (Ni(OH)2), NiCO3 (if CO2 is present during electrolysis) and analogous compositions for cobalt, manganese, and other transition metals. The process described herein may produce the transition metal cathode precursor materials (e.g., Ni(OH)2, Co(OH)2, Mn(OH)2), among others, in the solid state without producing large quantities of waste water.
In some examples, the transition metal hydroxide using some of the aspects described herein may generate a reaction product that does not require purification and/or washing of contaminants (e.g., NH3, K2SO4, NiSO4). For examples in which sodium chloride is present in the electrolyte, reaction product may include benign NaCl that may simply be removed by washing the reaction products with water. NaCl is less environmentally polluting and poses a lower threat to human health than the sulfates and ammonia produced by alternative processing techniques. For examples in which the electrolyte includes ammonium chloride (NH4Cl), remediation is also less problematic than other process. NH4Cl decomposes to a gaseous mixture of NH3 and HCl at 338° C. during calcination. The temperature of the gas mixture may be reduced below 338° C. after evolution of the gases so that NH4Cl condenses back into solid form, which can be recycled. For this reason, an impurity of NH4Cl salt requires no washing and therefore produces no wastewater.
While not wishing to be bound by theory, in some examples the porous carbon element 104 may reduce the activation energy of transferring an electron from a metal (e.g., the transition metal electrode 116) in electrical communication with the porous carbon to oxygen (via the conductor 120). This reduced activation energy may increase the rate at which a transition metal is oxidized when placed in electrical communication with the porous carbon. In some examples, an electrolyte (e.g., NaCl(aq)) may wet surfaces of the porous carbon element 104. This, in turn may facilitate the generation of hydroxy anions at the porous carbon element 104. The generated hydroxy anions may then diffuse to the transition metal electrode 116 and react with it to produce an oxidized form of the transition metal.
While not wishing to be bound by theory, the high specific surface area of porous carbon element 104 may be a factor in the efficient catalytic reduction of oxygen and subsequent oxidation of an electrolytically connected transition metal electrode 116. For example, porous carbon elements 104 that use carbonized aerogels, examples of which are described above, may have specific surface areas in the range of their non-pyrolyzed aerogel precursors from 100 m2/g to 600 m2/g.
While not wishing to be bound by theory, some examples of the porous carbon element 104 that comprise carbonized aerogels may comprise non-carbon “hetero atoms,” some of which may increase the efficiency by which oxygen is reduced and transition metals subsequently oxidized. For example, some carbon aerogels of the present disclosure derived from pyrolysis of polyimide aerogels may include residual nitrogen. In some examples, a residual nitrogen content of a carbon aerogel may be at least about 4 wt %. For example, carbon aerogels according to aspects disclosed herein can have a residual nitrogen content of at least about 0.1 wt %, at least about 0.5 wt %, at least about 1 wt % at least about 2 wt %, at least about 3 wt %, at least about 4 wt %, at least about 5 wt %, at least about 6 wt %, at least about 7 wt %, at least about 8 wt %, at least about 9 wt %, at least about 10 wt %, or in a range between any two of these values. Other heteroatoms that may participate in the reactions described herein may also include oxygen, hydrogen, graphitic carbon, in some examples.
While not wishing to be bound by theory, some examples of the porous carbon element 104 that comprise carbonized aerogel may have a relatively high electrical conductivity relative to other forms of carbon. The high electrical conductivity of the carbonized aerogel may facilitate the reduction of oxygen. In certain aspects, carbonized aerogel materials or compositions of the present disclosure have an electrical conductivity of about 1 S/cm or more, about 5 S/cm or more, about 10 S/cm or more, 20 S/cm or more, 30 S/cm or more, 40 S/cm or more, 50 S/cm or more, 60 S/cm or more, 70 S/cm or more, 80 S/cm or more, or in a range between any two of these values.
In some examples, the rate of the redox reaction (and more specifically, the oxidation of the transition metal) may be selected (e.g., increased or decreased relative to a reference reaction rate) by modifying one or more conditions under which the reaction is performed. In some examples, the rate of reaction may be increased by one or more of: increasing a temperature at which the reaction is performed, increasing a partial pressure of oxygen (thereby increasing a rate of hydroxy anion production), increasing a concentration of electrolyte (e.g., from a 1 molar (M) solution to a multiple molar solution), and/or increasing the magnitude of the electrical potential difference applied to the porous carbon/transition metal system 100. Similarly, a rate of reaction can be decreased by limiting any of the foregoing parameters. Changing a pH of the electrolyte or the composition of the electrolyte may also affect the rate of the reaction as well as the composition and morphology of the reaction product(s).
The porous carbon element 104 may be in a monolithic form, a particulate form, or combinations thereof.
In some examples, excluding gases other than oxygen may influence the reaction product. For example, using pure oxygen or a mix of gases that excludes carbon dioxide may reduce the presence of carbonate species in the reaction product. This in turn may reduce and/or eliminate the presence of undesired reaction products (e.g., carbonates) in the oxidized transition metal compounds.
The separator 108 is an electrically insulating material that provides a structure through which ions may travel. This combination prevents electrical shorting of the system 100 while enabling current flow via ionic transfer between the porous carbon element 104 and the transition metal electrode 116. Examples of separator 108 may include cellulose-based papers, fibrous polymer fabrics or felts, among others. Also, the separator can be eliminated if the electrodes are held physically apart (such as a flooded cell design).
The electrolyte 112, disposed within the separator 108, facilitates ionic transfer from the porous carbon element 104 to the transition metal electrode 116. Examples of the electrolyte include aqueous (e.g., distilled water, deionized water, distilled deionized water, tap water) solutions of sodium chloride (NaCl(aq)), ammonia chloride (NH3Cl(aq)), sodium carbonate (NaCO3(aq)), among others. In some examples, a concentration of the electrolyte may be saturated with solute. In other examples, a concentration of the electrolyte may be less than a saturated solution. In some examples, a concentration of the electrolyte may be selected according to various criteria including, but not limited to a desired rate of reaction at the transition metal anode (higher concentrations generally accelerating an oxidation rate), a morphology and/or configuration of the oxide reaction product at the transition metal anode, among others.
While not wishing to be bound by theory, it has been observed that the presence of chloride in the electrolyte promotes separation of the hydroxylated reaction product from the surface of the transition metal electrode 116. Thus, when using a chloride-containing electrolyte, the process may naturally convert an entire mass of the transition metal electrode 116 to the reaction product because a fresh surface of the transition metal electrode 116 is naturally exposed as the reaction progresses. In other examples, the configuration and/or morphology of the reaction product may be altered by changing the composition of the electrolyte, the pH of the electrolyte, or other similar parameters. For example, an electrolyte or pH may be changed so that the reaction product remains adhered to the transition metal electrode 116. An adhered reaction product may be beneficial in some examples, such as processing a transition metal electrode that has a layered or graduated composition and that retains its configuration during its processing into a rechargeable battery cathode. Such examples are described below in more detail.
The transition metal electrode 116 may be a piece of a transition metal that is in electrical and ionic communication with the porous carbon element 104 as illustrated in
In some examples, the transition metal electrode 116 may include compositional components that are not transition metals that are added to improve conductivity, improve oxidation reaction kinetics, and/or improve the conversion of the transition metal oxide/hydroxide into a cathode composition.
In some examples, such as those described below in Section 6 and
The conductor 120 may be an electrical conductor, such as a copper wire, an aluminum wire, a gold wire, and alloys thereof that connects the porous carbon element 104 and the transition metal electrode 116. In some examples, the conductor 120 may also be used to apply an electrical potential to the system 100 that initiates and sustains the oxidation reaction at the transition metal electrode 116.
A minimum applied electrical potential, applied in some examples via the conductor 120 from an external source, varies depending on the transition metal (or metals) selected for the transition electrode 116. The minimum applied electrical potential needed to promote an oxidation reaction at the transition metal oxide 116 may be an indication of the catalytic activity of the carbon catalyst used to reduce oxygen (e.g., for hydroxy anion generation) relative to the particular transition metal used as the transition metal electrode 116. An upper limit of the applied electrical potential may be based on the electrolyte. For purposes of illustration, an electrical potential applied to a water-based electrolyte may be selected to be below the voltage used for hydrolysis of water into oxygen and hydrogen. Electrolytes may be selected to sustain higher voltages.
Many of the elements shown in the electrochemical cell 200 of
The porous carbon element 216 is analogous to the porous carbon element 104. In some examples, the porous carbon element 216 is a carbon aerogel material formed by carbonizing a polyimide aerogel or a poly(amic) acid aerogel. In some examples, the porous carbon element 216 is a carbonized polyurethane foam. In some examples, the porous carbon element 216 is a combination or mixture of carbonized aerogel and carbonized polyurethane foam.
In addition to the elements already described in the context of
In particular,
The oxygen, upon encountering the porous carbon element 216 that also contains and/or is coated with the electrolyte 224, may be ultimately converted into hydroxy anions solvated by the electrolyte 224.
The hydroxy anions may then react with the transition metal component 208 to form one or more of transition metal oxides, hydroxides, and/or other reaction products 220 resulting from the reaction of transition metals and hydroxy anions. These reaction products are indicated by shaded region 220 in
In some examples, oxygen is the cathode in the electrochemical cell 200. That is, the oxygen that encounters the porous carbon element 216 (which functions as an “air cathode”) is reduced upon operation of the electrochemical cell 200. The arrows in
In some aspects, transition metal components reacted according to one or more of the aspects described above may be layered or graduated compositions. In some examples, the transition metal component may include two or more transition metals (e.g., Ni and Co; Ni, Co, and Mn). In some examples, the multiple transition metals are combined into an alloy that may have a uniform composition or may include multiple phases. In other examples, the multiple transition metals may include an intermetallic compound instead of, or in addition to, one or more alloys. In some examples, the composition may be graduated such that an exterior surface of a transition metal component is rich in one transition metal and gradually richer in another component as a distance to a center of the component decreases.
In other aspects, such as the one illustrated in
In one aspect, the transition metal component 400 may be processed according to the techniques described above to convert the outer layer 404 to its corresponding oxidized forms (e.g., oxides, hydroxides, peroxides). Some or all of the inner core 408 may be reacted to its corresponding oxidized forms. In one instantiation of this example, the outer layer 404 may be a first composition that includes cobalt and the inner core 408 may be a second composition that includes nickel. After oxidation and conversion to a cathode material upon thermal processing with a lithium salt, a cobalt-rich surface layer may decrease the rate of occurrence of NiO-side reactions that degrade cathode performance in more traditionally configured cathodes.
Some aspects herein may be applied to synthesize microporous and/or nanoporous materials by selectively oxidizing, at room temperature, one component of a multi-component and/or multi-phase system. For convenience of illustration, a two phase alloy of a first metal and a second metal may be formed in which the first metal may oxidize at a lower applied electrical potential than the second metal (when placed in an electrochemical cell with a carbon aerogel air cathode). In this way, regions of the alloy that are rich in the first alloy may be selectively oxidized and removed from the alloy. This technique may thus generate three-dimensional nanoporous elements that may have specific surface areas that are hundreds or thousands of square meters per gram. These high surface area metal components may be used as catalyst substrates, or themselves have a high surface chemical activity. In other examples, these techniques may be used to generate light-weight metal components that have mechanical properties (e.g., fracture toughness, elastic modulus, yield strength) that are comparable or better than their non-nanoporous analogs.
Oxidation of the metal corresponding to each of the metals shown in
The differences in onset voltage may be used to selectively oxidize one metal in an alloy, but not another with a different onset voltage. For example, aluminum and zinc form a solid solution of an aluminum-rich (a) phase and a zinc-rich (q) phase. In this example, aluminum may be oxidized preferentially, leaving pores having similar dimensions to the size of the a phase regions. Annealing and compositional parameters may be selected to alter the size of these a phase regions, thereby altering the size of the pores upon their removal. While cyclic voltammetery data is not shown for copper, aluminum and copper are known to form a solid solution. The techniques described herein may also be applied to aluminum-copper alloys, as well as many other types of alloys.
Similarly, mechanical processing may also be used to alter an onset voltage of a material. Mechanical deformation (e.g., exceeding a yield stress of a material) is known to promote oxidation at the location of the deformation. Bending, compressing, cold rolling (or other types of deformation), welding, and the like may be used to encourage preferential removal of material using the techniques described above.
In one experimental example, a configuration similar to that illustrated in
A nickel anode was inserted into (i.e., in direct contact) with the electrolyte solution and indirect contact with the carbon aerogel air cathode. The nickel anode was a section of pure nickel wire. A pure nickel current collector (the same material as the pure nickel anode) was placed in contact with the nickel anode. The nickel current collector was not in contact with the electrolyte. Both the pure nickel anode and the pure nickel current collector were purchased from TEMCo®.
To complete the circuit, a first end of a stainless-steel wire was placed in contact with the carbon aerogel air cathode. A second end (opposite the first end) of stainless-steel wire was placed in contact with the nickel current collector and Ni wire anode. Alligator clips were used to electrically connect the current collectors to a direct current voltage supply.
An external power source was used to apply a potential difference to the above electrochemical cell, where the carbon air cathode was connected to the negative terminal of the power source. In this example, approximately a 1 Volt (V) potential difference was applied to the carbon aerogel air cathode and the nickel current collector. In this experiment, the carbon aerogel air cathode was connected to a negative terminal of the power source and the nickel anode was connected to a positive terminal of the power source. The 1 V potential difference was selected for convenience and to avoid the parasitic water electrolysis reaction that reduces the coulombic efficiency of the system. Electrolysis of water also produces gaseous hydrogen and oxygen which additionally present a safety risk. The cyclic voltammetry data presented in
The reaction was performed in an ambient atmosphere (air) at standard temperature (˜20° C.) and pressure (1 atmosphere).
The electrochemical cell was then permitted to react under the conditions described above. The pure nickel anode reacted to completion in about 160 minutes. At this point, the portions of the nickel anode in contact with the electrolyte were consumed, thereby causing an open circuit between the electrolyte and the remaining stub of the anode that is no longer in contact with the electrolyte. The reaction product was disposed on the bottom of the beaker and had a green color consistent with Ni(OH)2, NiCO3 or a mixture of both.
The present inventors have surprisingly discovered that the methods of the present disclosure can also be used to produce both magnetic and non-magnetic iron oxide nanoparticles (IONPs) by using iron as the transition metal electrode 116 in a method analogous to that depicted in
First, in the disclosed method of producing magnetic IONPs, iron is used as the transition metal anode and a porous carbon element 104 may be used as described above, reducing the activation energy for the reduction of oxygen thereby enabling the electrically connected iron metal to participate in a room temperature redox reaction. The present inventors have found that a carbonized polyurethane foam maybe used in place of carbon aerogel as the element 104. In fact, the inventors believe that any porous carbon material may be used.
A carbonized polyurethane foam may be advantageous in the method of producing magnetic IONPs because it may be more chemically and mechanically stable than a carbon aerogel in the reaction that will be described below. In addition, the inventors believe that a combination of a carbonized polyurethane foam and carbon aerogel could be used in combination e.g., carbon aerogel stabilized within the pores of the carbonized polyurethane foam, wherein the carbonized polyurethane foam provides additional mechanical stability to the carbon aerogel material.
The production of magnetic IONPs may be described with reference to
The electrolytic reaction proceeds to oxidize the iron metal 208 to produce “green rust” which is iron (II) hydroxide (Fe(OH)2) and/or its partially oxidized form, Fe(OH)2-xOx. In practice this material precipitates and falls to the bottom of the reaction chamber and can be removed, for example by gravity or by pumping to a separate chamber. In the separate chamber the green rust may be allowed to stand and further oxidize partially under ambient conditions to form lepidocrocite (γ-FeO(OH)). This resulting (partially oxidized) iron hydroxide may be further forced to oxidize by bubbling air in basic conditions (e.g., pH>8) to yield magnetic IONPs and in particular maghemite γ-Fe2O3. The air bubbling may proceed at volumes of around 1-5 L/min, for example around 2 L/min. Magnetic IONPs (e.g., magnetite, maghemite, and/or their solid-solutions) are ferrimagnetic and can be magnetically separated from the reaction mixture (noting that iron oxy/hydroxides are paramagnetic). The recovered IONPs are then washed and dried for onward processing for example as the iron source in LFP synthesis.
Magnetic IONPs produced as described above have undergone XRD analysis and it has been confirmed that the observed XRD pattern matches the calculated pattern of the cubic spinel. The magnetic particles produced in this method are in the form of nanoparticles i.e. particles having a size in the region of 20-100 nm when observed using scanning electron microscopy. It has surprisingly been observed that the concentration of the electrolyte used in the process may have an influence on the particle size of the produced particles. For example, a 1M NaCl electrolyte has been shown to produce particles having a size of around 60-70 nm (specific surface area 22.46 m2/g) whereas a 0.2M KCl electrolyte has been shown to produce particles having a size of 20-40 nm (specific surface area 40.22 m2/g). Thus, the process may be tailored to produce particles of different size, depending on the intended end-use. Experimental example of making maghemite (γ-Fe2O3) nanoparticles.
The reaction was carried out in a 15 L rectangular plastic container filled with 10 L of 1 M NaCl solution, prepared in tap water. The air cathode comprised of four rectangular blocks of carbon foam, with dimensions of 4×10×16 cm. The air cathode blocks were secured in the reactor mechanically and connected electrically. Each carbon foam block has a central hole drilled along its length, through which air can be pumped. However, for the synthesis of magnetic γ-Fe2O3 (maghemite) no forced air diffusion is needed.
Foils of pure iron (˜15×2×0.04 cm) anodes were introduced between the carbon air cathodes and connected electrically. An overhead mixer with a mixing rate of ˜250 rpm was introduced in the reactor to homogenize the concentration of hydroxide reagents produced by the reduction of atmospheric oxygen. To begin, a voltage of 1 V was applied to the electrodes. Immediately, a current of ˜2 A starts to flow due to the following reactions:
½O2+H2O+2e→2OH− Cathode:
Fe→Fe2++2e Anode:
The magnitude of the current increases with time to around 4 Amperes(A), as corrosion increases the surface roughness of the Fe anode. The release of Fe2+ and OH− ions in the electrolyte beyond the solubility product constant results in the formation of nanoparticulate Fe(OH)2, i.e., the green rust. Partial oxidation of green rust through contact with atmospheric oxygen causes some oxidation to intermediate oxidations states, such as FeO1-x(OH)2-x (i.e., lepidocrocite) which adopts a cubic crystal structure similar to maghemite. After ˜24 h of reaction, the Fe anodes are corroded.
In a second step, the lepidocrocite fine sludge is extracted, the pH of the solution is increased to 9 by adding the appropriate amount of Na2CO3 and air is bubbled (1 L/min, 3 h) through the solution for oxidative dihydroxylation to maghemite, γ-Fe2O3. A magnet test is used to conclude complete conversion of lepidocrocite to maghemite. Next, the nanoparticulate maghemite is readily separated from the sodium chloride/carbonate electrolyte by magnetic separation and subsequent washes until free from the chloride ion (2˜3 washes with 1 L water each time).
The production of non-magnetic IONPs may proceed in part analogously to the production of magnetic IONPs described above, with reference to
The electrolytic reaction proceeds to oxidize the iron metal 208 to produce “green rust” which is iron (II) hydroxide Fe(OH)2 and/or its partially oxidized form, Fe(OH)2-xOx. In a first alternative method of the disclosure this material precipitates and falls to the bottom of the reaction chamber and can be removed, for example by gravity or by pumping to a separate chamber. In the separate chamber the green rust may be further forced to oxidize by bubbling air to yield non-magnetic IONPs and in particular goethite (FeOOH). The air bubbling may proceed at volumes of around 1-5 L/min, for example around 2 L/min. The nanoparticulate goethite is separated from the solution by at least one, and preferably a plurality of cycles of washing and decantation, or filtration, or centrifugation. The recovered IONPs are then dried for onward processing for example as the iron source in LFP synthesis.
In an alternative method of the disclosure the Fe(OH)2 formed in the electrolytic reaction may be directly oxidized to goethite nanoparticles in situ by the introduction of oxygen to the electrochemical cell, for example by bubbling air, optionally and conveniently through the porous carbon anode during electrolysis. The air bubbling may proceed at volumes of around 1-5 L/min, for example around 2 L/min. Such alternative method may be carried out in neutral to slightly acidic pH conditions (e.g., 5<pH<7, such as pH of about 6). The nanoparticulate goethite is separated from the sodium chloride electrolyte by analogous cycles of washing and decantation, or filtration, or centrifugation. The recovered IONPs are then dried for onward processing for example as the iron source in LFP synthesis.
The reaction was carried out in a 15 L rectangular plastic container filled with 10 L of 1 M NaCl solution, prepared in tap water. The air cathode comprised of four rectangular blocks of carbon foam, with dimensions of 4×10×16 cm. The air cathode blocks were secured in the reactor mechanically and connected electrically. Each carbon foam block has a central hole drilled along its length, through which air can be pumped as needed. Foils of pure iron (˜15×2×0.04 cm) anodes were introduced between the carbon air cathodes and connected electrically. An overhead mixer with a mixing rate of ˜250 rpm was introduced in the reactor to homogenize the concentration of hydroxide reagents. To begin, a voltage of 1 V was applied to the electrodes while air is pumped through the carbon cathodes at a rate of 2 L/min. Immediately, a current of ˜4 A starts to flow due to the following reactions:
½O2+H2O+2e→2OH− Cathode:
Fe→Fe2++2e Anode:
Due to the high concentration of dissolved O2 in the electrolyte, the as formed Fe(OH)2 nanoparticles oxidize directly to goethite nanoparticles. Under the above circumstances, complete etching of Fe anode occurs within 7-10 h.
Next, the nanoparticulate goethite is separated from the sodium chloride electrolyte by successive cycles of washing and decantation, or filtration, or centrifugation.
While not wishing to be bound by theory, the inventors believe that with all metals (M) capable of forming stable divalent cations (e.g., Fe, Mn, Ni, Co, Cu, Zn, Sn, etc.) the immediate reaction product formed at the surface of the M anode is the metal double hydroxide salt, M(OH)2. With metals for which +2 is the highest possible oxidation state (e.g., Zn) or where oxidation states higher than +2 are not energetically favorable to form at low temperature in air (e.g., Ni, Co, Cu), M(OH)2 seems to be the final reaction product as well. For the specific case of Fe (and Mn), as +3 oxidation states are readily available in air at low temperature, M(OH)2 tends to be an intermediate, leading to higher oxidation states depending on the potential-pH and oxidation conditions.
In the specific example of Fe, it seems that Fe(OH)2 and/or its partially oxidized form, FeOx(OH)2-x, i.e., the green rust, is the first intermediate that forms during electrolysis. Without any specific further treatment at neutral pH, green rust oxidizes slowly to goethite, FeO(OH). On the other hand, increasing the pH to above 8 and controlled oxidation by air, in the described method of the invention yields maghemite, Fe2O3 (or Fe8/3V1/3O4 in magnetite's spinel notation, where V=Vacancy). Due to availability of the +3 oxidation state for manganese, similar transformations are expected.
The inventors have found that either magnetic or non-magnetic IONPs can be produced by the methods of the present disclosure, by controlling the reaction conditions and in particular the oxygen from air that is available for oxidation. In the examples above, both performed at the same scale (15 L electrolytic reactor, 10 L electrolyte) the limited oxygen in the reactor when no air is bubbled through the carbon anode allows the green rust to oxidize to lepidocrocite FeO(OH), which later undergoes forced oxidation by air bubbling in alkaline conditions to magnetic maghemite Fe2O3. In the alternative, bubbling air during electrolysis in basic conditions causes the green rust to quickly oxidize directly to non-magnetic goethite FeO(OH). Thus it is the air and therefore oxygen that is introduced into the electrolyte which drives the oxidation in situ to the alpha form of the iron(III) oxide-hydroxide i.e. goethite, rather than the gamma form lepidocrocite. However, the inventors have also observed that when performing these reactions at a smaller scale (e.g., 1.5 L electrolyte), even with air bubbling through the carbon cathode, the reaction proceeds to lepidocrocite and then later maghemite. Without wishing to be bound by theory it is believed that in the smaller scale there is insufficient oxygen in the electrolyte to directly oxidize the green rust to goethite.
While the magnetic IONPs produced by methods of this disclosure have been described as useful for synthesizing LFPs, magnetic IONPs have many industrial uses such as in catalysts, in the defense industries e.g., as Microwave and Radar Absorbing Materials (RAMs), as ferrofluids, for recording tape, in remediation of pollution and in medical applications.
The method of producing magnetic IONPs as described is semi-continuous in that the electrochemical reaction may proceed in a first vessel and the product of the reaction may be transferred to a second vessel using a pump as described above while the electrochemical reaction continues and does not need to be stopped. The electrolyte may be reused thereby avoiding waste.
Table 1 presents particle size and specific surface area data for various experimental conditions. It will be noted that some embodiments include ball milling to access specific surface areas that are unexpectedly as much as 10 times greater than commercially available materials.
When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.
The invention may also broadly consist in the parts, elements, steps, examples and/or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and/or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein.
Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure.
Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/326,353 filed Apr. 1, 2022 entitled “Oxidation of Metals and Alloys Using a Carbon Aerogel Counter Electrode” and U.S. Provisional Patent Application No. 63/378,756 filed Oct. 7, 2022 entitled “Oxidation of Metals and Alloys Using a Porous Carbon Counter Electrode” both of which are herein incorporated by reference in their entirety
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2023/016824 | 3/30/2023 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63378756 | Oct 2022 | US | |
| 63326353 | Apr 2022 | US |
