Additive for improving durability of electrolytic cells

Abstract

The disclosed technology relates to a composition for mitigating hydrogen penetration and mitigating polymer oxidation by adding a radical scavenging organic inhibitor within an anion exchange membrane ("AEM") electrolysis cell.

Description

Background Technology

[0001] The disclosed technology relates to a composition for mitigating polymer oxidation by adding a free radical scavenging organic inhibitor within an electrolyzer employing an anion exchange membrane (“AEM”).

[0002] There are many different electrolysis systems. One example known to be where the anode generates free radicals or free radical precursors is water electrolysis, where these precursors can generate free radicals (such as hydrogen peroxide) during the electrolysis operation, leading to oxidative degradation. Another type of electrolysis system where the anode can generate free radicals is CO2 electrolysis, in which the anode nominally releases oxygen from the aqueous electrolyte.

[0003] One type of water electrolysis system is the anion exchange membrane electrolysis (AEMWE) system. Water electrolysis systems are promising hydrogen sources utilizing direct electrical energy; however, technological improvements are needed to replace current steam methane reforming (SMR) units for hydrogen production. Two major problems in water electrolysis are hydrogen crossover and oxidation of the solid ion-conducting medium (i.e., ionomers).

[0004] New strategies are needed to extend the durability of ionomers in electrolyzer membranes and electrodes to prolong their lifespan against oxidative degradation, and to minimize or stop hydrogen permeation for safer operation and purer product streams. Summary of the Invention

[0005] The disclosed technology addresses the degradation of ionomers in the membranes and electrodes of anion exchange membranes (“AEM”) electrolyzers by employing redox active molecules within the membrane, within the composite layer, within the electrode layer, and / or within the electrolyte of the electrolyzer.

[0006] Organic inhibitors for free radical scavenging can be stoichiometric (i.e., single-use) or can be regenerated to a free radical scavenging state (i.e., reduced) during electrolyzer operation via various mechanisms, including but not limited to hydrogen oxidation to mitigate hydrogen permeation, direct reduction at the electrodes, or any other chemical or electrochemical operation. Additives can be regenerated to a free radical scavenging state through numerous mechanisms, including but not limited to mitigating hydrogen permeation (i.e., hydrogen oxidation).

[0007] Therefore, in one aspect, the present technology provides a composition comprising (a)(i) a catalyst, (a)(ii) an ionomer or (a)(iii) a mixture of (a)(i) and (a)(ii), and (b) an organic inhibitor.

[0008] A method for extending the lifetime of ionomers in an electrolyzer and preventing hydrogen penetration to the anode is also provided. This method involves adding organic inhibitors to the electrodes, membranes, electrolytes, and / or composite layers of the electrolyzer, and then operating the electrolyzer.

[0009] In another embodiment, the technology includes an electrolyzer having (a) an electrode, (b) a membrane and (c) an electrolyte, wherein the electrolyte contains an organic inhibitor. Detailed Implementation

[0010] The preferred features and implementation schemes will now be described in a non-restrictive manner.

[0011] Unless otherwise stated, all part-weight levels of the components are based on 100 parts by weight of membrane ionomer, abbreviated as "phr".

[0012] An anion exchange membrane (“AEM”) electrolyzer is a device that produces valuable end products (such as hydrogen or reduced carbon dioxide products, such as methane or formate) through an electrochemical process called electrolysis. This electrochemical process is able to use electricity to produce, for example, hydrogen and oxygen molecules from an electrolyte (such as water), or to produce reduced carbon dioxide products, such as methane or formate.

[0013] An AEM electrolyzer comprises electrodes separated by membranes and optional composite layers that can be incorporated into or on the membranes. Applying voltage or current to the electrodes creates an electric field between them, which causes the electrolyte to break down into its components, such as hydrogen and oxygen. A complete system also includes pumps, power electronics, gas separators, and other auxiliary components, such as storage tanks.

[0014] Many components of an AEM electrolyzer, including electrodes and membranes, may include solid ion-conducting media, also known as ionomers. These ionomers are susceptible to degradation due to oxidation. To address this oxidation, organic inhibitors can be incorporated into these layers.

[0015] Organic inhibitors are compounds that mitigate the harmful oxidation of ionomer materials by chemical oxidants, such as the oxidative attack of peroxide radicals that may form during operation. When chemical oxidants are formed, organic inhibitors can be chemically oxidized, while the membrane and / or polymer material remains unoxidized.

[0016] In other words, during an oxidation event, the organic inhibitors will be oxidized, rather than the membrane and / or polymer materials being harmfully oxidized.

[0017] Organic inhibitors can have a redox potential greater than that of the anode electrode of the electrolyzer. Organic inhibitors must also not poison the catalyst in the electrode or any composite catalyst present on or within the membrane; that is, they must not reduce the catalyst's activity for the oxygen evolution and / or hydrogen evolution reactions to avoid adverse effects.

[0018] Organic inhibitors can be reversible. That is, after oxidation, a reversible organic inhibitor can be chemically and / or electrochemically reduced from its oxidized form back to a form that can be oxidized again, thus mitigating the harmful oxidation of other components by the oxidant. This reversibility between the oxidized and reduced states can occur, for example, through reaction with hydrogen passing through the electrolyzer membrane, or, for example, in reactions catalyzed by a composite catalyst. Therefore, reversible organic inhibitors can prevent not only membrane degradation but also hydrogen permeation.

[0019] The oxidation of reversible organic inhibitors must also have readily available kinetics, such that the oxidation of the molecule occurs at a perceptible rate prior to the membrane oxidation event, and that the subsequent reduction of the molecule (e.g., by reaction with hydrogen to an oxidized state) occurs prior to further subsequent oxidation catalyzed by a composite catalyst.

[0020] Those skilled in the art will be able to readily test compounds constituting reversible organic inhibitors using the techniques described herein. All such reversible organic inhibitors are covered under this disclosure.

[0021] Organic inhibitors can be selected from organic antioxidants, such as, for example, arylamines, diarylamines, alkylated arylamines, alkylated diarylamines, phenols, hindered phenols, sulfurized alkenes, sulfur heterocycles, arylamine heterocycles, terpenes, dithiocarbamates, phosphites, dithiophosphates, and hindered amines. In particular, phenolic antioxidants can be used, such as, for example, simple alkylphenols, hindered phenols, or coupled phenolic compounds. Hindered phenolic antioxidants often contain sec-butyl and / or tert-butyl groups as sterically hindered groups. The phenolic group can usually be further replaced by a hydrocarbon group (usually straight-chain or branched alkyl) and / or a bridging group connected to a second aromatic group. Examples of suitable hindered phenolic antioxidants include 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol, 4-ethyl-2,6-di-tert-butylphenol, 4-propyl-2,6-di-tert-butylphenol, or 4-butyl-2,6-di-tert-butylphenol, 4-dodecyl-2,6-di-tert-butylphenol, or butyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. In one embodiment, the hindered phenolic antioxidant may be an ester.

[0022] Coupled phenols typically contain two alkylphenols coupled to alkylene groups to form bisphenol compounds. Examples of suitable coupled phenolic compounds include 4,4'-methylenebis-(2,6-di-tert-butylphenol), 4-methyl-2,6-di-tert-butylphenol, 2,2'-bis-(6-tert-butyl-4-heptylphenol); 4,4'-bis(2,6-di-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol).

[0023] Diarylamines or alkylated diarylamines may be phenyl-α-naphthylamine (PANA), alkylated diphenylamines, or alkylated phenylnaphthylamines, or mixtures thereof. Alkylated diphenylamines may include dinonyl diphenylamine, nonyl diphenylamine, octyl diphenylamine, dioctyl diphenylamine, didecyl diphenylamine, decyl diphenylamine, and mixtures thereof. In one embodiment, the diphenylamine may include nonyl diphenylamine, dinonyl diphenylamine, octyl diphenylamine, dioctyl diphenylamine, or mixtures thereof. In one embodiment, the alkylated diphenylamine may include nonyl diphenylamine or dinonyl diphenylamine. Alkylated diarylamines may include octyl, dioctyl, nonyl, dinonyl, decyl, or didecylphenylnaphthylamine.

[0024] Other known examples of organic inhibitors include many hydroquinones / quinones, such as potassium 1,4-hydroquinone sulfonate; methyl 2,5-dihydroxybenzoate; 2,5-dihydroxybenzoic acid; 2,5-dihydroxybenzoic acid; 2,5-dimethoxybenzyl nitrile; 3,6-dihydroxyphthalonitrile; 3,4-dihydroxybenzoic acid; and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

[0025] The solid ion-conducting medium of the electrodes and / or membranes can be an ionomer polymer binder. The ionomer in the AEM electrolyzer can be a polymer that can conduct anions (e.g., OH-). - Any polymer that delivers anions to and from reaction sites within the electrolyzer. A "reaction site" is a catalyst site within the electrolyzer, such as in electrodes or composite layers. Generally, solid ion-conducting media or ionomers conduct negative ions (e.g., hydroxide ions).

[0026] In an AEM electrolyzer, any anion-conducting polymer can be used as an ionomer in the electrodes and membranes. Examples of anion-conducting polymers commonly used as ionomers and suitable for this invention are cationic-free base polymers, which have cationic groups that allow anion transport rather than cation transport. Commonly used cationic groups in AEM polymers include quaternary ammonium head groups, imidazolium-based groups, and nitrogen-free groups such as phosphonium, thioonium salts, and ligand-metal complexes. Cationic-free base polymers to which cationic groups can be bonded include those based on poly(aryl ethers), polyolefins (poly(ethylene), poly(propylene)), and polyphenylene oxides, and examples include backbones containing cationic moieties. Some examples include hexamethyltrimethylammonium-functionalized Diels-Alder polyphenylene polyphenylene (“HTMA-DAPP”), quaternized polycarbazole (“QPC-TMA”), poly(2,2'-m-phenylene-5,5'-bibenzimidazole) (“m-PBI”), and poly(fluorene-co-terphenyl) (“PFTP”).

[0027] The electrodes and membranes of an AEM electrolyzer may also include non-ionic conductive materials to help maintain the integrity of the electrodes and / or membranes. Examples of non-ionic conductive materials may include polymers such as polyvinyl alcohol, polyacrylate, polymethacrylate, functionalized polyethylene oxide, functionalized polypropylene oxide; thermoplastic polyurethane, polytetrafluoroethylene, to name a few. Again, the non-ionic conductive material is not limited and can be any material now known or developed in the future that helps maintain the integrity of the membrane.

[0028] Conductive electrodes, or simply electrodes, may also include ionomer binders and / or nonionic conductive materials as described above, as well as optional organic inhibitors.

[0029] The electrode will further include an electrode catalyst. The catalyst can be any electrode catalyst now known or developed later, including metallic or non-metallic catalysts. Metallic catalysts can be, for example, noble metals or transition metals or any alloys thereof. Examples of such metals include, for example, ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, silver, copper, rhenium, mercury, iron, cobalt, and nickel. In one embodiment, the metallic catalyst is platinum or a platinum alloy.

[0030] The conductive electrode will also include at least one solid ion-conducting medium to bind the catalyst together and conduct anions (i.e., OH-) - Anions are transported to and from reaction sites within a specific electrode (anode or cathode) and help disperse electrode components. Any solid anion-conducting polymer can be used as an ionomer, such as those described above.

[0031] Especially for catalysts, there are alternative embodiments that simply mix the catalyst and organic inhibitor with the ionomer. In an alternative embodiment, the organic inhibitor can be immobilized onto the ionomer by functionalization, and then the functionalized ionomer can be mixed with the catalyst and optionally a nonionic conductive material. Alternatively, the entire mixture can be mixed with a solvent to prepare the ink.

[0032] When present, the amount of organic inhibitor in the electrode layer can be in the range of 1 phr to 50 phr based on the total electrode catalyst content, or 2 phr to 40 phr based on the total electrode catalyst content, or even 3 phr to 37 phr based on the total electrode catalyst content, or 4 phr to 35 phr based on the total electrode catalyst content, or even 5 phr to 34 phr based on the total electrode catalyst content.

[0033] The membrane layer of the electrolyzer is also composed of the ion-conducting medium described above, providing multiple functions, including the transport of anions and the separation of the anode and cathode electrodes.

[0034] When present in the membrane layer, the amount of organic inhibitor may be in the range of 0.1 mol% to 25 mol% relative to the ionic portion of the ionomer, or 0.2 mol% to 20 mol% relative to the ionic portion of the ionomer, or 0.3 mol% to 15 mol% relative to the ionic portion of the ionomer, or 0.4 mol% to 10 mol% relative to the ionic portion of the ionomer, or 0.5 mol% to 5 mol% relative to the ionic portion of the ionomer.

[0035] The membrane layer may also include a metal-hydrogen composite catalyst or a non-metal-hydrogen composite catalyst (also referred to as a "composite catalyst" or simply a "catalyst") that promotes the oxidation of hydrogen. The metal-hydrogen composite catalyst can be a noble metal or a transition metal or any alloy thereof. Examples of such metals include, for example, ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, silver, copper, rhenium, mercury, iron, cobalt, and nickel. In one embodiment, the metal-hydrogen composite catalyst is platinum or a platinum alloy. This composite catalyst is used to consume hydrogen gas passing through a separator from the hydrogen production side of the system to the oxygen production side.

[0036] In one embodiment, the present technology provides a composition comprising a composite catalyst and a reversible organic inhibitor. The combination of the composite catalyst and the reversible organic inhibitor is contained within a membrane and is not in explicit contact with an electrode. This can be a discrete continuous layer within the membrane or a random dispersion throughout the membrane. The composite catalyst and the reversible organic inhibitor can be simply mixed together and physically contacted, or the reversible organic inhibitor can be immobilized onto the composite catalyst. Immobilization can be, for example, by covalently bonding the reversible organic inhibitor to the composite catalyst and / or the organic material constituting the catalyst layer via methods known in the art.

[0037] In particular, regarding composite catalysts, there is an alternative embodiment whereby the composite catalyst and the reversible organic inhibitor are prepared first. In this alternative embodiment, the reversible organic inhibitor can be immobilized onto the ionomer by functionalization, followed by mixing the functionalized ionomer with the composite catalyst; or the reversible organic inhibitor can be immobilized onto the composite catalyst by functionalization, followed by mixing the functionalized ionomer with the ionomer, optionally mixed with a non-ionic conductive material in each case.

[0038] When present in the membrane composite layer, the amount of reversible organic inhibitor can be in the range of 1 phr to 50 phr based on the total composite catalyst content, or 2 phr to 40 phr based on the total composite catalyst content, or even 3 phr to 37 phr based on the total composite catalyst content, or 4 phr to 35 phr based on the total composite catalyst content, or even 5 phr to 34 phr based on the total composite catalyst content.

[0039] An AEM electrolyzer will include electrodes, a membrane, and an electrolyte. The electrolyte is a conductor of ions and can include any electrolyte now known or to be developed in the future. For this purpose, example electrolytes include solutions of inorganic salts in water, dilute acids, and dilute bases, such as alkaline solutions of sodium hydroxide or potassium hydroxide, which in particular can carry organic inhibitors through the system. In one embodiment, the technology covers an electrolyzer having (a) electrodes, (b) a membrane, and (c) an electrolyte, wherein the electrolyte contains an organic inhibitor.

[0040] In one embodiment, the present technology provides an ionomer additive composition. The ionomer additive composition may include an ionomer, an optional nonionic conductive material, and an organic inhibitor.

[0041] In one embodiment, the present technology provides an ionomer additive composition. The ionomer additive composition may include an ionomer, a composite catalyst, an optional nonionic conductive material, and an organic inhibitor.

[0042] In one embodiment, the present technology provides an electrode composition. The electrode composition may include an ionomer, optionally a nonionic conductive material, an organic inhibitor, and an electrode catalyst.

[0043] The technology also includes a method for preventing the degradation of ionomers in an electrolyzer. This method includes adding an organic inhibitor to the electrolyzer and operating the electrolyzer.

[0044] This technology allows for a method to prevent ionomer oxidation and hydrogen permeation within the electrolyzer by including organic inhibitors in the membrane layer of the electrolyzer and operating the electrolyzer.

[0045] It also includes a method for extending the lifespan of ionomers and / or membrane materials in an electrolyzer by adding an organic inhibitor to an electrolyte placed in the electrolyzer and operating the electrolyzer.

[0046] Unless otherwise stated, the amounts of each chemical component described do not include any solvents or diluents that are commonly found in commercial substances, i.e., based on active chemicals. However, unless otherwise stated, each chemical or composition mentioned herein should be interpreted as a commercial-grade substance that may contain isomers, byproducts, derivatives, and other such substances generally understood to be present in commercial-grade forms.

[0047] It is known that some of the substances described above can interact in the final formulation, such that the composition of the final formulation may differ from those initially added. For example, metal ions can migrate to other acidic or anionic sites of other molecules. The resulting products, including those formed when the compositions of the present invention are used for their intended purpose, may not be easily described. However, all such modifications and reaction products are included within the scope of the present invention; the present invention includes compositions prepared by mixing the above-described components.

[0048] Unless otherwise expressly stated, all numerical quantities of material amounts, reaction conditions, molecular weights, carbon number, etc., specified in this specification should be understood as being modified by the word "about". It should be understood that the upper and lower limits of the quantities, ranges, and proportions described herein can be combined independently. Similarly, the ranges and quantities of each element of this invention can be used in conjunction with the ranges or quantities of any other element.

[0049] As used herein, the transitional term “comprising,” synonymous with “comprising,” “containing,” or “characterized in,” is inclusive or open-ended and does not exclude additional, unlisted elements or method steps. However, in every use of “comprising” herein, it is intended that the term also cover the phrases “consistently composed of” and “composed of” as alternative embodiments, wherein “consisting of” excludes any elements or steps not specified, and “consisting of” allows the inclusion of additional, undescribed elements or steps that do not substantially affect the essential or essential and novel characteristics of the composition or method under consideration.

[0050] While certain representative embodiments and details have been shown to illustrate the purpose of this invention, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention. In this regard, the scope of the invention is defined only by the following claims.

Claims

1. A composition comprising: (a)(i) a catalyst, (a)(ii) an ionomer or (a)(iii) a mixture of (a)(i) and (a)(ii), and (b) an organic inhibitor.

2. The composition according to claim 1, wherein the organic inhibitor comprises an organic inhibitor capable of cycling between an oxidized state and a reduced state, i.e., a reversible organic inhibitor.

3. The composition according to claim 2, wherein the organic inhibitor is reversible through a chemical mechanism.

4. The composition according to claim 2, wherein the organic inhibitor is reversible via an electrochemical mechanism.

5. The composition according to any of the preceding claims, wherein the organic inhibitor comprises a substance that decomposes peroxides.

6. The composition according to any of the preceding claims, wherein the organic inhibitor comprises a free radical scavenger.

7. The composition according to any of the preceding claims, wherein the organic inhibitor is capable of chemically oxidizing hydrogen or driving electrochemical hydrogen oxidation.

8. The composition according to any of the preceding claims, wherein the ion-conducting ionomer conducts anionic substances.

9. The composition according to any of the preceding claims, wherein the composition further comprises a non-ionic conductive material.

10. The composition according to claim 1, wherein the catalyst is a composite catalyst.

11. The composition according to any of the preceding claims, wherein the composite catalyst comprises a noble metal.

12. The composition according to any of the preceding claims, wherein the composite catalyst comprises platinum.

13. The composition according to any of the preceding claims, wherein the composite catalyst comprises ruthenium.

14. The composition according to any of the preceding claims, wherein the composite catalyst comprises a transition metal.

15. The composition according to any of the preceding claims, wherein the composite catalyst comprises iron.

16. The composition according to any of the preceding claims, wherein the composite catalyst comprises nickel.

17. The composition according to any of the preceding claims, wherein the composite catalyst comprises an alloy of any of the aforementioned substances.

18. The composition according to any of the preceding claims, wherein the composite catalyst comprises a non-metallic composite catalyst.

19. The composition according to claim 1, wherein the catalyst is an electrode catalyst.

20. The composition of claim 19, wherein the catalyst comprises a noble metal.

21. The composition according to claim 19, wherein the catalyst comprises platinum.

22. The composition of claim 19, wherein the catalyst comprises ruthenium.

23. The composition of claim 19, wherein the catalyst comprises a transition metal.

24. The composition of claim 19, wherein the catalyst comprises iron.

25. The composition of claim 19, wherein the catalyst comprises nickel.

26. The composition of claim 19, wherein the catalyst comprises an alloy of any of the foregoing substances.

27. The composition of claim 19, wherein the catalyst comprises a nonmetallic catalyst.

28. The composition according to any of the preceding claims, wherein the organic inhibitor is immobilized onto the ionomer by functionalization.

29. A method for preventing the degradation of ionomers in an electrolyzer, the method comprising including an organic inhibitor in the electrolyzer and operating the electrolyzer.

30. The method of claim 29, wherein the organic inhibitor is contained in the membrane layer of the electrolyzer.

31. The method of claim 29, wherein the membrane comprises a composite catalyst.

32. The method of claim 29, wherein the organic inhibitor is contained in the electrodes of the electrolyzer.

33. The method of claim 29, wherein the organic inhibitor is contained in an electrolyte circulating through the electrolyzer.

34. A method for preventing hydrogen penetration into an electrolyzer, the method comprising including an organic inhibitor in a composite layer of the electrolyzer, and operating the electrolyzer.

35. An electrolyzer comprising (a) an electrode, (b) a membrane and (c) an electrolyte, wherein the electrolyte contains an organic inhibitor.

36. A method for extending the lifetime of ionomers and / or membrane materials in an electrolyzer, the method comprising adding an organic inhibitor to an electrolyte placed in the electrolyzer, and operating the electrolyzer.

37. The method of claim 36, wherein the organic inhibitor comprises a substance that decomposes peroxides.

38. The method of claim 36, wherein the organic inhibitor comprises a free radical scavenger.