Improved anodes with reduction in oxidation and species poisoning for electrochemical devices

Abstract

Described herein is the use of a platinum ruthenium (PtRu) anode catalyst that provides reduced oxidation and species poisoning in an electrochemical cell performing electrocatalysis. The described anode catalyst may be useful for the conversion of CO and CO2 to organic compounds including formic acid. The described catalyst may be implemented into perforated ion exchange membrane electrode assemblies.

Description

IMPROVED ANODES WITH REDUCTION IN OXIDATION AND SPECIES POISONING FOR ELECTROCHEMICAL DEVICESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Patent Application No. 63 / 697.051, filed on September 20, 2024, the contents of which are incorporated herein by reference in their entirety.CONTRACTUAL ORIGIN

[0002] This invention was made with government support under Contract No. DE-AC36- 08G028308 awarded by the Department of Energy'. The government has certain rights in the invention.BACKGROUND

[0003] Electrocatalysis may play an important role in the use and conversion of greenhouse gas pollutants into useful products, providing an economic means for carbon capture or sequestration. As an example, both carbon dioxide and carbon monoxide may be electrocatalyzed into useful organic compounds including formic acid. Recent advances in the electrocatalysis of CO and CO2 using ion exchange membranes can be seen in US Patent Publication No. 2024 / 0191366 and International Patent Publication No. WO 2024 / 124228, which are hereby incorporated by reference in their entirety. However, certain species, including CO and CO2, are problematic to electrocatalyze due to anode oxidation and species poisoning, which increase the required electricity / energy input and can cause periodic voltage oscillation within the electrochemical cell. It can be seen from the foregoing that there remains a need in the art for improved anodes and electrochemical cells in the field of electrocatalysis and membrane electrode assembly architecture to reduce anode oxidation and species poisoning.SUMMARY

[0004] Described herein is the use of a platinum ruthenium (PtRu) anode catalyst that provides reduced oxidation and species poisoning in an electrochemical cell performing electrocatalysis. The described anode catalyst may be useful for the conversion of CO and CO2 to organic compounds including formic acid. The described catalyst may be implemented into perforated ion exchange membrane electrode assemblies.

[0005] In an aspect, provided is a device comprising: a) an anode comprising Pt and at least one of Ni, Co, Cr, Mn, Zn, V, Ti, Ru, Rh, Pd, Ir. Os. Sn. Sb. Pb. Bi, Ga. In, Ge, Se, Te, La, Ce, Pr, Nd, Fe and Cu; b) a cathode: and c) at least one ion exchange membrane positioned between the anode and the cathode.

[0006] In an aspect, provided is a method comprising: a) providing an electrochemical cell comprising: i) an anode comprising Pt and at least one of Ni, Co, Cr, Mn, Zn, V, Ti, Ru, Rh, Pd, Ir, Os, Sn, Sb, Pb, Bi, Ga, In, Ge, Se, Te, La, Ce, Pr, Nd, Fe and Cu; ii) a cathode; and iii) at least one ion exchange membrane positioned between the anode and cathode; b) generating an electrical current between the anode and the cathode; and c) flowing CO or CO2 gas to the cathode, thereby reacting the CO or CO2 gas and generating organic compounds.

[0007] The anode may comprise Pt and Ru, for example, as a catalyst. The device may be an electrochemical cell or a membrane electrode assembly useful for the conversion of CO or CO2 to organic compounds, including formic acid and the conversion of CO to CO2. For the sake of clarity, CO and CO2 are considered an "‘organic compound" as used herein and the cell may convert CO2 to CO or vice versa.

[0008] The ion exchange membrane may be perforated, as described in US. Patent Pub. 2024 / 0191366, for example, having a void space selected from the range of 0.1% to 50% of a surface area of the perforated ion exchange membrane. The ion exchange membrane may also be coated with a catalyst. The ion exchange membrane may comprise two different membrane, one anionic and one cationic membrane with the additional features described herein.

[0009] The cathode may be a gas diffusion electrode. The anode may further comprise a catalyst supported on carbon nanoparticles having a diameter less than or equal to 5000 nm, 2500 nm, 1000 nm, or optionally 500 nm. The cathode may further comprise a catalyst comprising nanoparticles having a diameter less than or equal to 2500 nm, 1000 nm, 500 nm, or optionally, 250 nm.

[0010] The catalyst may be alloyed with or otherwise supported by carbon, e.g., PtRu / C. The catalyst may be comprised of about 50 wt% Pt and 50 wt% Ru, greater than 30 wt% Pt, 40 wt% Pt, 50 wt% Pt, 60 wt% Pt, 70 wt% Pt, or optionally. 80 wt% Pt or greater than 30 wt% Ru, 40 wt% Ru, 50 wt% Ru, 60 wt% Ru, 70 wt% Ru, or optionally, 80 wt% Ru (wherein the previous weight percentages ignore the weight of any carbon support or alloying).BRIEF DESCRIPTION OF DRAWINGS

[0011] Some embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.

[0012] Figure 1 provides an exemplary cross-sectional schematic of an electrochemical cell utilizing a perforated ion exchange membrane and a PtRu catalyst, as described herein.

[0013] Figure 2A illustrates a membrane electrode assembly (MEA) architecture with anion exchange membrane (AEM) and perforated cation exchange membrane (CEM), and different pathways for formic acid transport. Figures 2B-2C show durability’ (Figure 2B) and faradaic efficiency (Figure 2C) for the first three hours versus time at 200 mA / cm2.

[0014] Figure 3A illustrates the gas diffusion layer (GDL) cell setup with different anode catalyst coated gas diffusion electrode (GDE) as working electrode. Figure 3B provides the FA oxidation mechanism via direct and indirect pathways. Figures 3C-3D provide potential vs. time and corresponding CO2 ppm vs. time at 200 mA / cm2using Pt / C anode catalyst (Figure 3C) and 100 mA / cm2using PtRu / C anode catalyst (Figure 3D). Figure 3E provides current density vs. potential while scanning the potential at scan rate of 10 mV / s using different anode catalyst in an electrolyse containing 1.0 M FA in 0.5 M sulfuric acid and continuous H2 flow at 2 seem and Figure 3F provides corresponding ppm of CO2 for the same conditions.

[0015] Figures 4A-4D provide FE at different current densities (50 to 500 mA / cm2) using PtPd / C (Figure 4A), Pd / C (Figure 4B), Pt / C (Figure 4C), and PtRu / C anode catalyst (Figure 4D). Figure 4E provides Cell voltage at different current densities using different anode catalysts. Figure 4F provides 10 hours of % FA loss and % FA FE vs. time at 200 mA / cm2using different anode catalysts.

[0016] Figure 5A shows cell voltage vs. time at 200 mA / cm2while using different anode catalysts. Figures 5B-5F provide FE vs. time for 60 hours using Pd (Figure 5B), 60 hours using PtPd (Figure 5C), 60 hours using Pt (Figure 5D), 125 hours using Pt (Figure 5E), and 100 hours using PtRu anode catalyst (Figure 5F).REFERENCE NUMERALS100 Electrochemical cell110 Perforated ion exchange membrane120 Anode130 Cathode140 Electrode (cathode)150 Cathode catalyst160 Anion exchange membrane170 Anode catalyst180 Electrode (anode)190 Gas reactant flow chamber200 Product flow chamberDETAILED DESCRIPTION

[0017] The embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein. References in the specification to "‘one embodiment”, "an embodiment”, “an example embodiment”, “some embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0018] As used herein the term “substantially” is used to indicate that exact values are not necessarily attainable. By way of example, one of ordinary skill in the art will understand that in some chemical reactions 100% conversion of a reactant is possible, yet unlikely. Most of a reactant may be converted to a product and conversion of the reactant may asymptotically approach 100% conversion. So, although from a practical perspective 100% of the reactant is converted, from a technical perspective, a small and sometimes difficult to define amount remains. For this example of a chemical reactant, that amount may be relatively easily defined by the detection limits of the instrument used to test for it. However, in many cases, this amount may not be easily defined, hence the use of the term “substantially”. In some embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 20%, 15%, 10%, 5%, or within 1% of the value or target. In further embodiments of the present invention, the term “substantially” is defined as approaching aspecific numeric value or target to within 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1% of the value or target.

[0019] As used herein, the term ‘‘about’' is used to indicate that exact values are not necessarily attainable. Therefore, the term “about” is used to indicate this uncertainty limit. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±20%, ±15%, ±10%, ±5%, or ±1% of a specific numeric value or target. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±1%, ±0.9%, ±0.8%, ±0.7%, ±0.6%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, or ±0.1% of a specific numeric value or target.

[0020] The membrane electrode assembly (MEA) architecture (Fig. 2A) with the perforated CEM layer provides pathways for the migration of formic acid and anions through the CEM / AEM interface, benefiting in reduced species accumulation. Carbon supported Pt (Pt / C) anode catalyst was utilized to oxidize continuously flowing Eh to H+, which combines with the formate to target formic acid (FA) generation. Results for the initial 3 hours of durability test while holding constant current density of 200 mA / cm2is shown in Figs. 2B-2C. Increase in the cell voltage can be observed within 30 mins which stabilized thereafter while having a periodic oscillation in the voltage (Fig. 2B). Faradaic efficiency (FE) for FA oxidation / loss at the anode (Fig. 2C) can be observed to increase correspondingly which can be related to accumulation of FA with time. With the increasing concentration of FA. FA will enter the anode catalyst layer as the diffusion of FA through the membrane itself can occur along with transportation through the membrane perforation. Result suggests that the formic acid oxidation rate (FAOR) over the anode surface results in the increase of cell voltage and the oscillation.

[0021] Gas diffusion electrode (GDE) cell coupled with time-of-flight mass spectrometry (TOF-MS) as shown in Fig. 3A was utilized to verify the undergoing mechanism during FAOR and quantify and compare the amount of CO2 generated while using different anode catalysts (Pt, Pd, PtPd, and PtRu). Fig. 3B shows FAOR mechanism via direct and indirect pathways. Fig. 3C shows the potential and corresponding CO2 response while holding a constant current density of 200 mA / cm2while using Pt catalyst. Indirect pathway of FAOR generates surface adsorbed carbon monoxide (CO) which acts as poison for HOR resulting in the sudden increase of potential as observed. Once the CO oxidation / stripping potential is reached, the CO2 ppm increases followed by drop in potential because of removal of CO poison from the catalyst surface. Fig. 3D is the similar study while using PtRu catalyst at 100 mA / cm2current density.Repetition of poisoning and stripping mechanism results in the anodic potential oscillations which verifies that the cell voltage oscillations during the current-hold durability test (Fig. 2B) occurs due to FAOR. Fig. 3E shows the current response while scanning the potential while using different catalyst and Fig. 3F shows the corresponding CO2 ppm. PtRu generates lower amount of CO2 relative to other anode catalyst.

[0022] Different anode catalysts were employed in the MEA, and the FE loss for FA oxidation at the anode (Fig. 4D) and the cell voltage (Fig. 4E) at different current densities are clearly lower for PtRu catalyst as expected from the results of GDE cell-based studies. Fig. 4F shows that FE for FA is higher and the FE for FA loss is lower at 200 mA / cm2for 10 hours while using PtRu anode catalyst, which is desired for the optimum anode catalyst. The durability result is also consistent for longer time (Fig. 5F). Due to lower FAOR loss, the cell voltage is also relatively lower while using PtRu anode catalyst (Fig. 5A).

[0023] The provided discussion and examples have been presented for purposes of illustration and description. The foregoing is not intended to limit the aspects, embodiments, or configurations to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the aspects, embodiments, or configurations are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the aspects, embodiments, or configurations, may be combined in alternate aspects, embodiments, or configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the aspects, embodiments, or configurations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects he in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. While certain aspects of conventional technology have been discussed to facilitate disclosure of some embodiments of the present invention, the Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate aspect, embodiment, or configuration.

[0024] The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will be obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional composition and processing elements and steps.

[0025] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to "a cell" includes a plurality of such cells and equivalents thereof known to those skilled in the art. As well, the terms "a" (or "an"), "one or more" and "at least one" can be used interchangeably herein. It is also to be noted that the terms "comprising", "including", and "having" can be used interchangeably. The expression ‘"of any of claims XX-YY " (wherein XX and YY refer to claim numbers) is intended to provide a multiple dependent claim in the alternative form, and in some embodiments is interchangeable with the expression “as in any one of claims XX-YY.”

[0026] When a group of substituents is disclosed herein, it is understood that all individual members of that group and all subgroups, are disclosed separately. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. For example, when a device is set forth disclosing a range of materials, device components, and / or device configurations, the description is intended to include specific reference of each combination and / or variation corresponding to the disclosed range.

[0027] Every formulation or combination of components described or exemplified herein can be used to practice the invention, unless otherwise stated.

[0028] Whenever a range is given in the specification, for example, a density range, a number range, a temperature range, a time range, or a composition or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges givenare intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.

[0029] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments that are in the prior art. For example, when composition of matter is claimed, it should be understood that compounds known and available in the art prior to Applicant's invention, including compounds for which an enabling disclosure is provided in the references cited herein, are not intended to be included in the composition of matter claims herein.

[0030] As used herein, “comprising” is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of' excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of' does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each instance herein any of the terms "comprising", "consisting essentially of' and "consisting of' may be replaced with either of the other two terms. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[0031] All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be w ithin the scope of this invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A device comprising: an anode comprising Pt and at least one of Ni, Co, Cr, Mn, Zn, V, Ti, Ru, Rh, Pd, Ir, Os, Sn, Sb, Pb, Bi, Ga, In, Ge, Se, Te, La, Ce, Pr, Nd, Fe and Cu; a cathode; and at least one ion exchange membrane positioned between the anode and the cathode.

2. The device of claim 1, wherein the anode comprises Pt and Ru.

3. The device of claim 1 or 2, wherein the device is an electrochemical cell for the conversion of CO or CO2 to organic compounds via electrolysis.

4. The device of any of claims 1-3, wherein the at least one ion exchange membrane comprises a perforated ion exchange membrane.

5. The device of claim 4, wherein the perforated ion exchange membrane has void space selected from the range of 0. 1% to 50% of a surface area of the perforated ion exchange membrane.

6. The device of any of claims 1-5, wherein the at least one ion exchange membrane comprises a coated membrane.

7. The device of any of claims 1-6. wherein the at least one ion exchange membrane comprises: a cationic exchange membrane; and an anionic exchange membrane.

8. The device of any of claims 1-7, wherein the cathode is a gas diffusion electrode.

9. The device any of claims 2-8, wherein the anode comprises greater than or equal to 30 wt% Ru.

10. The device of any of claims 1-9, wherein the anode further comprises a catalyst supported on carbon nanoparticles having a diameter less than or equal to 5000 nm.

11. The device of any of claims 1-10, wherein the cathode further comprises a catalyst comprising nanoparticles having a diameter less than or equal to 1000 nm.

12. A method comprising: providing an electrochemical cell comprising: an anode comprising Pt and at least one of Ni, Co. Cr, Mn, Zn, V. Ti, Ru. Rh, Pd, Ir, Os. Sn. Sb. Pb. Bi, Ga. In, Ge, Se, Te, La, Ce, Pr, Nd, Fe and Cu; a cathode; and at least one ion exchange membrane positioned between the anode and cathode; generating an electrical current between the anode and the cathode; and flowing CO or CO2 gas to the cathode, thereby reacting the CO or CO2 gas and generating organic compounds.

13. The method of claim 12, wherein the anode comprises Pt and Ru.

14. The method of claim 12 or 13, wherein the at least one ion exchange membrane comprises a perforated ion exchange membrane.

15. The method of claim 14, wherein the perforated ion exchange membrane has void space selected from the range of 0. 1% to 50% of a surface area of the perforated ion exchange membrane.

16. The method of any of claims 12-15, wherein the at least one ion exchange membrane comprises: a cationic exchange membrane; and an anionic exchange membrane.

17. The method of any of claims 12-16, wherein the organic compounds comprise formic acid.

18. The method of any of claims 13-17, wherein the anode comprises greater than or equal to 30 wt% Ru.

19. The method of any of claims 12-18, wherein the anode further comprises a catalyst supported on carbon nanoparticles having a diameter less than or equal to 5000 nm.

20. The method of any of claims 12-19, wherein the cathode further comprises a catalyst comprising nanoparticles having a diameter less than or equal to 1000 nm.

21. The method of any of claims 12-20, wherein the step of flowing comprises flowing CO2 gas to the cathode, thereby reacting the CO2 to generate CO.

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