Recycling of catalyst coated membrane components

Abstract

Disclosed is a method of recycling a spent catalyst coated membrane material comprising an ionomer, at least one catalyst comprising platinum, palladium and / or ruthenium, and at least one catalyst comprising an iridium binary oxide, the method comprises: (a) treating the spent catalyst coated membrane material with a heated solution comprising an acid and an oxidizing agent wherein platinum, palladium and / or ruthenium are leached from the spent catalyst coated membrane material into the solution that is separated from the remaining solid components of the spent catalyst coated membrane material; (b) treating the spent catalyst coated membrane material with a solvent to disperse ionomers and recover a dispersion of ionomers, wherein the dispersion of ionomers is performed before or after the leaching of platinum, palladium and / or ruthenium in step (a); and (c) after recovering platinum, palladium and / or ruthenium and ionomers in steps (a) and (b), treating the residual spent catalyst coated membrane material by one of three specified processes to extract iridium.

Description

TECHNICAL FIELD

[0001] This specification relates to recycling methods for components of catalyst-coated membranes, such as those used in fuel cells and hydrogen-producing water electrolyzers. BACKGROUND

[0002] Fuel cell and hydrogen-producing water electrolyzer production will grow rapidly with investment in a global hydrogen economy. Catalyst-coated membranes (CCMs) are a primary functional component of both fuel cells and electrolyzers. Such CCMs typically include a conductive polymer membrane coated on either side with a catalyst-containing layer. CCMs are configured to drive oxidation and reduction reactions and support proton and electron transport, processes needed for fuel cell and electrolyzer technology to function.

[0003] While there are variations in CCM component materials and configurations depending on functional performance requirements in end-use applications, they generally contain several valuable components, including one or more platinum group metal (PGM) catalysts and one or more proton-conducting polymers.

[0004] Typically, the membrane is formed from one or more ionomer, such as a perfluorosulfonic acid (PFSA) ionomer. Ionomer can also be provided in one or both of the catalyst layers. The ionomer in the catalyst layers can be the same or different from the main membrane component and / or the ionomer in the other catalyst layer.

[0005] A CCM can include two different catalysts, one to drive an oxidation reaction on one side of the CCM and one to drive a reduction reaction on the other side of the CCM. A CCM can also include a reforming catalyst provided to catalyze the reforming of hydrogen and oxygen to form water, reducing the amount of hydrogen passing through the membrane and mixing with oxygen to form a potentially explosive mixture. A CCM can also include a metal oxide (e.g., Ce02) as a peroxide scavenger.

[0006] CCM catalysts can be based on platinum group metals, such as platinum, ruthenium, iridium, palladium, or mixtures thereof. Platinum group metals can be provided in elemental (metal) form, in compound form (e.g., oxides, such as iridium oxide catalyst), or as a PGM-based metal alloy (e.g., PtCo). In addition, PGM catalyst materials can be supported on a base material (e.g., carbon, such as a carbon-supported platinum catalyst including carbon microparticles having platinum disposed thereon or carbon-supported PtCo).

[0007] Catalyst-coated membranes (CCMs) can also be provided in conjunction with additional functional layers to form a multi-layer membrane electrode assembly (MEA). Such MEAs can have, for example, 3, 5, or 7 layers.

[0008] With the increase in CCM manufacturing for fuel cells and electrolyzers, there is an associated increase in CCM waste, including an increase in production scrap (e.g., due to quality control failures) and end-of-life (EoL) CCMs formed during CCM manufacturing. Since CCMs contain several rare and / or valuable components, including platinum group metals (particularly Pt, Pd, Ir, and Ru) and ionomers (in both the membrane and catalyst layers), there is a growing need for methods to recycle such components from waste CCM materials.

[0009] One current method for recovering PGMs from production scrap and end-of-life CCM materials involves incineration. The incineration process produces an ash rich in PGMs (typically Pt and Ir) that is processed via conventional PGM refining routes. However, the incineration process releases harmful and toxic gases, such as CO2 and HF, from the polymers that are part of the membrane. Both of these gases have negative impacts as they pollute the atmospheric environment, increase the greenhouse effect, and / or have harmful effects on the human body. Thus, there is a need for a cleaner process that reduces or eliminates the emission of these gases.

[0010] In addition to the above, the incineration method destroys the ionomer components, which also have important value. Thus, it is also desirable to provide a process that is able to recover both PGMs and ionomer components and to provide a cleaner, safer, and more environmentally friendly process. Processes for recovering perfluorosulfonic acid ionomers are known. See, e.g., WO2016 / 156815 and US7255798. In addition, processes for recovering individual PGM catalyst components are known. See, e.g., US7709135. However, in order for fuel cells and electrolyzers to become more sustainable technologies, a commercially viable and environmentally friendly route is needed to recover, separate, and recycle both PGMs and ionomer components from waste CCM materials, including production scrap and end-of-life materials.

[0011] It is an object of the present specification to solve this problem. SUMMARY

[0012] This specification relates particularly to the recycling of spent catalyst-coated membrane materials comprising ionomer, at least one catalyst comprising platinum, palladium and / or ruthenium and at least one catalyst comprising iridium binary oxide such as iridium tantalum oxide (IrTaOx) and / or iridium ruthenium oxide (IrRuOx). Iridium binary oxides present particular challenges as they are well-known stable catalysts and are therefore resistant to simple acid dissolution and purification methods that can be used for other catalyst materials. This specification provides a method that is able to recover all platinum group metal components as well as ionomer components from spent catalyst-coated membrane materials comprising iridium binary oxides such as iridium tantalum oxide (IrTaOx) and / or iridium ruthenium oxide (IrRuOx).

[0013] According to the present specification, there is provided a method of recycling spent catalyst-coated membrane materials comprising ionomer, at least one catalyst comprising platinum, palladium and / or ruthenium and at least one catalyst comprising iridium binary oxide such as IrTaOx and / or IrRuOx, the method comprising:

[0014] (a) treating the spent catalyst-coated membrane material with a solution comprising an acid and an oxidizing agent, wherein platinum, palladium and / or ruthenium is leached from the spent catalyst-coated membrane material into the solution, the solution being separated from the remaining solid components of the spent catalyst-coated membrane material;

[0015] (b) treating the spent catalyst-coated membrane material with a solvent to disperse the ionomer and recover a dispersion of ionomer, wherein the dispersion of ionomer is performed before or after the leaching of platinum, palladium and / or ruthenium in step (a); and

[0016] (c) after the recovery of platinum, palladium and / or ruthenium and ionomer in steps (a) and (b), treating the residual spent catalyst-coated membrane material by one of three processes to extract iridium:

[0017] (i) directly recovering iridium as a solid iridium binary oxide catalyst material after the leaching of platinum, palladium and / or ruthenium and the dispersion and recovery of ionomer;

[0018] (ii) subjecting the iridium binary oxide to a peroxide fusion process, wherein the iridium binary oxide material is mixed with an alkali fusion flux, heated in a furnace and then subjected to acid dissolution to recover iridium in solution;

[0019] (iii) subjecting the iridium binary oxide to one or more pyrometallurgical processes including smelting to separate platinum group metals, followed by acid dissolution of platinum group metals and a series of hydrometallurgical processes to separate and purify individual platinum group metals including iridium.

[0020] The process is based on the recognition that the iridium binary oxide component is the most stable component and is advantageously recovered after recovery of the platinum, palladium and / or ruthenium components and the ionomer component. In this regard, it has been found that the iridium binary oxide component is not leached by leach processes that can be used to recover the platinum, palladium and / or ruthenium components. Furthermore, it has been found that the iridium binary oxide component meets the specification requirements for reuse in fuel cell applications after being subjected to oxidative acid leach conditions used to recover the platinum, palladium and / or ruthenium components. Thus, according to route (c)(i) of the process of the present application, the iridium binary oxide catalyst material can be recovered for direct reuse without the need for metal separation, purification and re-synthesis of a new iridium binary oxide catalyst material.

[0021] As an alternative to direct recovery and reuse of the iridium binary oxide catalyst material, the iridium component of the binary oxide material can be recovered. However, while reductive acid leaching can be used to recover iridium from non-iridium binary oxide catalyst materials, such reductive acid leach processes do not provide high iridium recovery yields for iridium binary oxide catalyst materials. According to the present specification, two alternative routes are available in addition to the direct recovery route (c)(i).

[0022] According to route (c)(ii), the iridium binary oxide is subjected to a superoxide fusion process in which the iridium binary oxide material is mixed with an alkali fusion flux, heated in a furnace and then subjected to acid dissolution to recover the iridium in solution. The superoxide fusion process is currently performed by analytical laboratories to determine the iridium binary oxide material. In the present specification, this known method is transferred from an analytical analysis context to a recycling method for recovering iridium (and optionally other metal components of the binary oxide) from the spent iridium binary oxide material produced after separation of the platinum and ionomer components.

[0023] Alternatively, according to route (c)(iii), the iridium binary oxide can be fed into a PGM refinery circuit in which the material is subjected to one or more pyrometallurgical processes, including smelting, to separate the platinum group metals, followed by acid dissolution of the platinum group metals and a series of hydrometallurgical processes to separate and purify individual platinum group metals including iridium. Optionally, the residual iridium binary oxide containing material can be ashed to remove any residual ionomer prior to entering the refinery circuit. Advantageously, this method can use existing PGM refinery processes to separate and purify iridium (and optionally other metal components of the binary oxide) from the spent iridium binary oxide material produced after separation of the platinum and ionomer components. However, compared to the more tailored recycling methods of routes c(i) and c(ii), the recycling time can be longer.

[0024] Further details of the process are provided in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0025] For a better understanding of the present application, and to show how it can be carried into effect, there will now be described by way of example only, certain embodiments of the application, with reference to the accompanying drawings in which:

[0026] Figure 1 A waste CCM recycling process according to the present specification is shown;

[0027] Figure 2 FTIR data for a fluorinated polymer film material, a fluorinated polymer salt material formed after treatment in water and base, and a fluorinated polymer salt material formed after treatment in water and base followed by water wash are shown;

[0028] Figure 3 An example of a process step (pre-autoclaving) including refluxing a fluorinated polymer film in a basic LiOH solution to form a fluorinated polymer salt without dispersing the film, followed by water wash is shown;

[0029] Figure 4 are photographs showing the film before (left hand side) and after (right hand side) the process step of refluxing the film in a basic LiOH solution and washing with water;

[0030] Figure 5 Another step of autoclaving the film after the treatment process as shown in Figure 3 is shown to disperse the polymer salt in water; and

[0031] Figure 6 Another step of ion exchange (post-autoclaving) is shown to convert the dispersed polymer salt back to the protonated acid form. DETAILED DESCRIPTION

[0032] As described in the SUMMARY and as explained in Figure 1 According to one aspect of the present specification, there is provided a method of recycling a waste catalyst-coated film material comprising an ionomer, at least one catalyst comprising platinum, palladium and / or ruthenium, and at least one catalyst comprising iridium binary oxide (e.g. IrTaOx and / or IrRuOx), the method comprising:

[0033] (a) treating the waste catalyst-coated film material with a solution comprising an acid and an oxidizing agent, wherein platinum, palladium and / or ruthenium leaches from the waste catalyst-coated film material into the solution, the solution being separated from the remaining solid components of the waste catalyst-coated film material;

[0034] (b) treating the waste catalyst-coated film material with a solvent to disperse the ionomer and recover a dispersion of ionomer, wherein the dispersion of the ionomer is performed before or after the leaching of platinum, palladium and / or ruthenium in step (a); and

[0035] (c) after recovery of platinum, palladium and / or ruthenium and ionomer in steps (a) and (b), the residual spent catalyst coated membrane material is treated to extract iridium by one of three processes:

[0036] (i) after leaching of platinum, palladium and / or ruthenium and dispersion and recovery of ionomer, the iridium is recovered directly as a solid iridium binary oxide catalyst material;

[0037] (ii) subjecting the iridium binary oxide to a peroxide fusion process in which the iridium binary oxide material is mixed with an alkali fusion flux, heated in a furnace, and then subjected to acid dissolution to recover iridium in solution;

[0038] (iii) subjecting the iridium binary oxide to one or more pyrometallurgical processes, including smelting, to separate platinum group metals, followed by acid dissolution of the platinum group metals and a series of hydrometallurgical processes to separate and purify individual platinum group metals including iridium.

[0039] In step (a), the acid used in the leaching of platinum, palladium and / or ruthenium can be hydrochloric acid. The oxidizing agent used for the leaching can be chlorate, chlorine gas or hydrogen peroxide. The oxidizing agent concentration can be: at least 0.001 mol / l, 0.005 mol / l or 0.01 mol / l; no more than 1 mol / l, 0.5 mol / l or 0.10 mol / l; or within a range defined by any combination of the above lower and upper limits (e.g., within a range of 0.01 mol / l to 0.10 mol / l). The acid concentration can be: no less than 4 M, 5 M or 5.5 M; no more than 7 M, 6.5 M or 6 M; or within a range defined by any combination of the above lower and upper limits. The leach solution can be heated, optionally to a temperature of: at least 50 °C, 60 °C or 70 °C; no more than 160 °C, 100 °C or 90 °C; or within a range defined by any combination of the above lower and upper limits, where if the solution is heated above 100 °C, this is done in a pressurized vessel.

[0040] These leaching conditions have been found to be effective in leaching platinum, palladium and / or ruthenium catalyst materials. In addition, these leaching conditions do not leach any of the iridium binary oxide in the iridium binary oxide. The leaching process has little effect on the microstructure, crystallography and composition of the iridium binary oxide, and the iridium binary oxide remains in a form that can be directly reused in the manufacture of new CCM components.

[0041] As specified in step (b) of the method, the ionomer is dispersed, either before or after the leaching step described above, and the resulting ionomer dispersion is separated from the remaining waste catalyst coated membrane material comprising iridium binary oxide. The solvent used to disperse the ionomer can be selected from water, a basic aqueous solution, an organic solvent, an alcohol, or a mixture of an alcohol and water. In the ionomer dispersion step, the solvent can be heated at a temperature of at least 150°C, 180°C, 200°C, 220°C, 230°C, or 240°C; no more than 400°C, 300°C, 275°C, or 250°C; or within a range defined by any combination of the foregoing lower and upper limits. The heating can be performed in an autoclave.

[0042] According to certain preferred methods, the ionomer can be treated with a base (e.g., an aqueous solution of a metal hydroxide or an ammonium hydroxide such as LiOH) to convert the ionomer to a salt form. The solid ionomer material can be treated without dispersing the solid ionomer material, provided that the material is not heated to the above-mentioned temperatures of the dispersion step. The excess base can then be removed and replaced with another solvent (e.g., water) before the ionomer is dispersed in the solvent by heating in an autoclave, as previously described. Alternatively, the basic aqueous solution can be used as the solvent in which the ionomer is dispersed by heating. However, one advantage of first converting the solid ionomer to a salt form and then dispersing the ionomer in a different solvent is that the excess base can be removed prior to the ionomer dispersion, so that the ionomer dispersion is not contaminated with excess base.

[0043] Once the ionomer and platinum, palladium, and / or ruthenium catalyst materials are removed, the remaining waste catalyst coated membrane material comprises iridium binary oxide and potentially other components such as carbon and / or membrane reinforcing materials. Advantageously, the iridium binary oxide is separated from any other remaining components prior to further processing. For example, a slurry of the remaining waste material can be formed and filtered to separate the solid components according to their different particle sizes. The recovered iridium binary oxide can then be washed and dried in preparation for reuse in a new catalyst ink formulation.

[0044] While it has been found that the iridium binary oxide material can be directly recovered in an acceptable form for reuse in this manner, if the recovered binary oxide material does not meet the specifications for a particular application, or if it is desired to recover the individual metal components separately, the individual metal components can be recovered and purified separately. According to route (c)(ii) of the method, the iridium binary oxide is subjected to a peroxide fluxing process in which the iridium binary oxide material is mixed with an alkali fluxing agent, heated in a furnace, and then subjected to acid dissolution to recover the iridium in solution. Other metals in the binary oxide (e.g., Ta or Ru) can also be recovered via this route.

[0045] Alternatively, iridium can be recovered via route (c)(iii) in which the iridium binary oxide is subjected to one or more pyrometallurgical processes, including smelting, to separate the platinum group metals, followed by acid dissolution of the platinum group metals and a series of hydrometallurgical processes to separate and purify individual platinum group metals including iridium. Other metals in the binary oxide (e.g. Ta or Ru) can also be recovered via this route.

[0046] The methods described herein can be applied to waste catalyst coated membrane material in the form of a catalyst coated membrane or a ionomer containing catalyst material that has been separated from an ionomer membrane.

[0047] Example

[0048] Platinum recovery

[0049] CCM-HCl / chlorate leach

[0050] A process has been developed to leach PGMs from CCM production waste. The recovered PGM material is then refined using existing PGM refining processes. For such processes, there are strict limits on the fluorine content (<1%) of the PGM material introduced into the PGM refining process. This is considered a potential problem for leaching PGMs from waste CCM material as CCMs are made primarily from fluorine containing polymers. The leaching process of the present invention enables PGMs to be leached without introducing significant amounts of fluorine into the leachate.

[0051] HCl / chlorate solution was used to dissolve Pt from CCM. Ir is in oxide form in CCM and no significant amount of Ir was leached, enabling separation of Pt and Ir. Chlorate was used in the form of an added sodium chlorate solution, introduced using a peristaltic pump.

[0052] A fuel cell CCM was loaded into the vessel (cut into pieces of approximately 2 cm x 3 cm). 400 mL of 6M HC1 (solution prepared from concentrated HC1 and distilled H20) was loaded into the flask and the stirring speed was set to 250 rpm. The reaction mixture was heated to 70 °C. During heating, a light yellow colour of the solution could be seen.

[0053] 4 mL of NaCIO3 solution (450 g / L) was added at a rate of approximately 0.09 mL / min. After the addition of the NaCIO3 solution was complete, the reaction mixture was cooled to room temperature. The reaction mixture was filtered through 0.45 pm filter paper, resulting in a yellow solution (365 mL). The liquid was collected and the remaining CCM pieces were washed with distilled H20 (86 mL). The CCM pieces were picked out and arranged on a surface dish to dry in air overnight.

[0054] IC / ICP analysis indicated that the leaching conditions did not leach Ir to any significant degree. In contrast, approximately 100% of the Pt was leached into the leach liquor. The liquor also showed an undetectable amount of fluoride, indicating that the leaching conditions were not destructive to the ionomer in the CCM.

[0055] Thus, it has been shown that this method can be used to recover Pt from waste CCM material without damaging the ionomer material of the CCM or introducing fluorine into the Pt treatment stream for subsequent Pt refining. It has also been shown that Pt can be leached from waste CCM material without leaching iridium, thus enabling the separation and recovery of Pt and Ir for reuse. Thus, using this method, Pt, Ir, and ionomer components (and optionally ruthenium or palladium if present) can be recovered.

[0056] Ionomer recovery

[0057] A piece of perfluorosulfonic acid ionomer membrane was cut into a small enough piece to fit into a container. 6.0 g of anhydrous LiOH and 250 g of water were weighed and the LiOH was dissolved in the water. The piece of membrane was submerged in the LiOH solution and heated to reflux for 1 hour. The resulting mixture was washed with 4 x 100 mL of water. The remaining water was decanted to leave the (wet) membrane piece. 250 g of water was weighed and added to the (wet) membrane piece and heated to reflux for 1 hour. The water was then decanted and the solid product was dried under vacuum.

[0058] Figure 2 FTIR data showing salt formation is shown. FTIR data was collected for untreated fluorinated polymer membrane material 301, fluorinated polymer salt material formed after treatment in aqueous LiOH solution 303, and fluorinated polymer salt material formed after treatment in aqueous LiOH solution followed by water wash 304.

[0059] Figure 3 An example of a process step (pre-autoclave) is shown. The membrane on the roll is cut and then further cut or folded to size. As indicated by the figure, the membrane is brown. The membrane is then refluxed in a lithium hydroxide solution, where the membrane turns colorless and converts to a salt form, which is confirmed by spectroscopic analysis. The conversion is achieved without dispersing the membrane, which remains in a solid, undispersed form.

[0060] It can be noted that the color change of the membrane does not necessarily indicate a chemical change, and the membrane can have different colors. However, in the illustrative example, the chemical change of the polymer from the protonated form to the salt form is accompanied by an associated color change, as shown in the figure.

[0061] In Figure 3 In the final step of the pre-autoclave process shown, the solid polymer salt membrane material is washed in water to remove any residual LiOH solution.Figure 4 are photographs showing the film before (left-hand side) and after (right-hand side) the process step of refluxing the film in basic LiOH solution and washing with water, indicating the change in colour of the film from brown to colourless and the fact that the film remains in a solid, undispersed form. Spectroscopic analysis confirmed that the colourless film was in the form of a salt.

[0062] Figure 5 shows another step of autoclaving the film after the treatment process shown to disperse the film in water. The colourless, solid, undispersed polymeric salt film was autoclaved in water at 250 °C and 40 bar (4000 kPa) pressure under nitrogen. This produced an aqueous dispersion of the polymeric salt (non-basic). Figure 3

[0063] Figure 6 shows another step of ion exchange (post-autoclaving) to convert the dispersed polymeric salt back to the protonated acid form. An ion exchange column containing Amberlyst® 15 (H) resin was used for this process step. The dispersion of the (protonated) fluorinated polymer can be reused to make new films or dried and stored for future use. ™ 15 (H) resin was used for this process step. The dispersion of the (protonated) fluorinated polymer can be reused to make new films or dried and stored for future use.

[0064] Iridium recovery

[0065] IrTaOx is found in some catalyst powders used for fuel cell applications to increase the stability of the system. However, oxidation leaching experiments using peroxide and NaCI03 have shown 0% recovery of Ir when leaching IrTaOx. This provides the possibility of direct recovery and reuse of IrTaOx as a catalyst powder.

[0066] To understand if the residue of the leaching can be directly recycled, powder characterisation has been carried out and compared to the starting material to see how the leaching conditions affect the material structure. If there is no significant change in the structure, it can be recycled, optionally blended with new material.

[0067] ​To test whether iridium binary oxides can be directly recycled and reused as catalyst materials in fuel cell catalyst coated membranes using the methods as described herein, samples of the material have been subjected to an oxidative acid leaching process for the recovery of platinum (or alternatively palladium or ruthenium). Samples of the solid iridium binary oxide material recovered after the platinum leaching process have then been analyzed using SEM, XRD, ICP and nitrogen gas BET surface area measurements to determine whether they meet the specifications for reuse as catalysts in new fuel cell catalyst coated membranes. To determine whether there are any changes depending on the specific leaching process used for the recovery of platinum, one set of samples was subjected to HC1 acid leaching using peroxide as oxidant and another set of samples was subjected to HC1 acid leaching using NaClO3 as oxidant.

[0068] SEM analysis

[0069] SEM images of the iridium tantalum oxide starting material were taken. After being subjected to HC1 acid leaching using H2O2 as oxidant, additional SEM images of the iridium tantalum oxide were taken. After being subjected to HC1 acid leaching using NaClO3 as oxidant, additional SEM images of the iridium tantalum oxide were taken.

[0070] Visual inspection of the SEM images indicated that the particulates were more fragmented and / or had a smaller particle size when NaClO3 was used as oxidant. This indicates that NaClO3 is a more aggressive oxidant than peroxide. The images of the starting material appear more similar in structure compared to the sample leached with peroxide, which indicates that peroxide does not cause much damage to the structure and can be better for direct recycling.

[0071] After analyzing the SEM data, it was decided to leach more IrTaOx using HC1 / NaClO3 because from the SEM analysis it was visible that this sample had more differences compared to the starting material and would therefore be more likely to benefit from the data collected in the QC analysis. Using NaClO3 as oxidant also more closely resembles the conditions using Cl2(g), which is more likely to be used as oxidant when the process is run at a larger scale.

[0072] XRD analysis

[0073] XRD analysis of the sample leached with NaClO3 showed that the phase is Ir / Ta oxide and the single crystalline phase determined by XRD is within the product specifications for average crystallite size and composition for IrTaOx catalyst materials.

[0074] ICP analysis

[0075] The leached residue was sent for ICP analysis, which showed that the Ir and Ta contents were within the specification limits for the IrTaOx catalyst material. The impurities in the sample were also within the specification limits. The Fe content was also below the specified limit, as was the Cl content. In summary, the leached sample passed the specification criteria for the ICP results.

[0076] Nitrogen BET analysis

[0077] The BET surface area was measured and was also within the specification limits for the IrTaOx catalyst material, so the leached material also passed this criterion.

[0078] Conclusion

[0079] The testing with the IrTaOx powder showed that the material still met the product specification after exposing the catalyst to the Pt leaching process. The results indicate that a direct recycling route for iridium binary oxide materials is feasible.

[0080] Superoxide fusion

[0081] As an alternative to direct recovery and reuse of iridium binary oxide catalyst material, iridium and other metals can be recovered using a peroxide fusion process. Peroxide fusion has been used to process samples of iridium binary oxide catalyst powder for analysis. The iridium binary oxide catalyst powder is mixed with an alkali fusion flux, heated in a furnace, and then subjected to acid dissolution to recover the iridium in solution. Other metals in the binary oxide, such as Ta or Ru, can also be recovered via this route. For example, iridium binary oxide can be mixed with sodium peroxide, heated in a furnace, and then acid leached. An example of this method of processing iridium is described in the paper “Chemical Dissolution of Iridium Powder Using Alkali Fusion Followed by High-Temperature Leaching” by Jaeryeong Lee and Youngjin Kim, Materials Transactions, Vol. 52 (2011) No. 11. This paper describes an alkali fusion process with Na2O2 followed by leaching in an HC1 solution to dissolve the iridium. The alkali fusion with Na2O2 is described as allowing Ir to be easily oxidized to IrO2, which is converted to a higher oxidation state via combination with Na-Ir-O at 600 °C for 4 hours. From a fused mixture with a molar ratio of 1 :2.0 (Ir:Na2O2), Ir can be completely leached using an HC1 solution with a concentration higher than 3 M at 130 °C. Furthermore, leaching with 3 M HC1 at 130 °C can dissolve Ir from a mixture fused at 600 °C regardless of the molar ratio with Na2O2. Ir can also be completely dissolved at 70 °C or lower when the fused mixture has a ratio of 1 :2.0. According to the present specification, a corresponding process can be used to recover iridium from iridium binary oxide catalyst powder used in CCMs. However, in the case of IrTaOx catalysts, the use of HF in addition to HC1 is required to support the separation of tantalum.

[0082] Large scale fusion has been used to process materials. Thus, this represents a viable alternative route for recovering iridium (and other metals in binary oxides).

[0083] Pyrometallurgical route

[0084] As an alternative to using the peroxide fluxing process as described above, the iridium binary oxide material can be supplied into an existing PGM refining process that involves pyrometallurgical processing followed by acid dissolution and hydrometallurgical separation and purification of the PGMs. The pyrometallurgical route can require an ashing step to burn off residual ionomer prior to entering the existing refining circuit to follow the existing process for refining PGM feed. For example, the material can be smelted in a reverberatory furnace at over 1200 °C for about 12 hours to separate the non-metallic components and produce an iron-based feed containing PGMs. The bullion feed is subjected to acid leaching to concentrate the PGMs into solution, followed by a series of solvent extraction, evaporation, precipitation, and filtration steps to separate and purify the PGMs.

[0085] Summary

[0086] The present specification provides a flow diagram for the recovery of Pt (or alternatively Pd or Ru), ionomer, and IrTaOx (and alternative Ir binary oxides) from fuel cell membrane electrode assemblies (MEAs) and catalyst coated membranes (CCMs). The Pt can be recovered by oxidative leaching using HC1 as the acid, using chlorine, hydrogen peroxide, or sodium chlorate as the oxidizing agent. The remaining residue is then subjected to an ionomer dispersion process, but it should be noted that ionomer recovery and Pt recovery can occur in either order. The remaining residue contains primarily IrTa oxide or alternative binary oxides such as IrRu oxide and some carbon. This can then be subjected to a selection of recovery methods. One route is to employ separation techniques to recover IrTaOx directly as a catalyst powder, ready for reuse. Alternatively, the residue can be subjected to a peroxide fluxing process, currently carried out by analytical laboratories to assay the material, and barium peroxide fluxing has been carried out on a large scale. This would allow the Ir to go into solution and then can be processed using known techniques to purify the material. Another option is to allow the material to enter an existing refining circuit so that it follows a pyrometallurgical route. The residue can be ashed prior to entering the refining circuit.

[0087] Accordingly, the present specification allows for the recovery of all PGMs and ionomer in a spent CCM material containing iridium binary oxides such as IrTaOx.

[0088] While the application has been particularly shown and described with reference to certain examples, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the scope of the application as defined by the appended claims.

Claims

1. A method for coating a membrane material with recycled spent catalyst, wherein the membrane material comprises an ionomer, at least one catalyst comprising platinum, palladium and / or ruthenium, and at least one catalyst comprising an iridium binary oxide, the method comprising: (a) Treat the membrane material coated with the spent catalyst with a solution containing an acid and an oxidant, wherein platinum, palladium and / or ruthenium are leached from the membrane material coated with the spent catalyst into the solution, the solution being separated from the remaining solid components of the membrane material coated with the spent catalyst; (b) Treating the membrane material coated with the spent catalyst with a solvent to disperse the ionomer and recovering the dispersion of the ionomer, wherein the dispersion of the ionomer is carried out before or after the leaching of the platinum, palladium and / or ruthenium in step (a); and (c) After recovering the platinum, palladium and / or ruthenium and ionomer in steps (a) and (b), the residual spent catalyst-coated membrane material is treated by one of the following three processes to extract iridium: (i) After the leaching of the platinum, palladium and / or ruthenium and the dispersion and recovery of the ionomer, the iridium is directly recovered as a solid iridium binary oxide catalyst material; (ii) subjecting the iridium binary oxide to a peroxide melting process, wherein the iridium binary oxide material is mixed with an alkaline melting flux, heated in a furnace, and then subjected to acid dissolution to recover the iridium from the solution; (iii) subjecting the iridium binary oxide to one or more pyrometallurgical processes, including smelting, to separate platinum group metals, followed by acid dissolution of the platinum group metals and a series of hydrometallurgical processes to separate and purify individual platinum group metals including iridium.

2. The method according to claim 1, The iridium binary oxide mentioned therein is iridium tantalum oxide or iridium ruthenium oxide.

3. The method according to claim 1 or 2, In step (a), the acid used for leaching platinum, palladium, and / or ruthenium is hydrochloric acid.

4. The method according to any of the preceding claims, In step (a), the oxidant used for the leaching of platinum, palladium and / or ruthenium includes chlorate, chlorine or hydrogen peroxide.

5. The method according to any of the preceding claims, In step (a), the solution used for leaching platinum, palladium, and / or ruthenium has the following oxidant concentrations: at least 0.001 mol / L, 0.005 mol / L, or 0.01 mol / L; not exceeding 1 mol / L, 0.5 mol / L, or 0.10 mol / L; or within any combination of the lower and upper limits described above.

6. The method according to any of the preceding claims, In step (a), the solution used for leaching platinum, palladium, and / or ruthenium has the following acid concentrations: not less than 4M, 5M, or 5.5M; not more than 7M, 6.5M, or 6M; or within any combination of the lower and upper limits described above.

7. The method according to any of the preceding claims, In step (a), the leaching solution for platinum, palladium, and / or ruthenium is heated, optionally to a temperature of at least 50°C, 60°C, or 70°C; not exceeding 160°C, 100°C, or 90°C; or within any combination of the lower and upper limits described above, wherein if the solution is heated above 100°C, this is done in a pressurized vessel.

8. The method according to any of the preceding claims, In step (b), the solvent used to disperse the ionomer is selected from water, alkaline aqueous solution, organic solvent, alcohol, or a mixture of alcohol and water.

9. The method according to any of the preceding claims, In step (b), the solvent used to disperse the ionomer is heated at the following temperatures: at least 150°C, 180°C, 200°C, 220°C, 230°C, or 240°C; not exceeding 400°C, 300°C, 275°C, or 250°C; or within any combination of the lower and upper limits described above.

10. The method according to any of the preceding claims, In step (b), before dispersing the ionomer in the solvent, the ionomer is treated with an alkali to convert the ionomer into a salt form.

11. The method according to any of the preceding claims, In step (c), the solid iridium binary oxide catalyst material is separated from other residual components of the membrane material coated with the spent catalyst by forming a particulate suspension and filtering it to separate the components by particle size.

12. The method according to any of the preceding claims, In step (c), the iridium is recovered via route (i), in which the iridium is directly recovered as a solid iridium binary oxide catalyst material after the leaching of the platinum, palladium and / or ruthenium and the dispersion and recovery of the ionomer.

13. The method according to any one of claims 1 to 11, In step (c), the iridium is recovered via route (ii), in which the iridium binary oxide is subjected to a peroxide melting process, in which the iridium binary oxide material is mixed with an alkaline melting flux, heated in a furnace, and then subjected to acid dissolution to recover the iridium in the solution.

14. The method according to any one of claims 1 to 11, In step (c), the iridium is recovered via route (iii), in which the iridium binary oxide is subjected to one or more pyrometallurgical processes, including smelting, to separate platinum group metals, followed by acid dissolution of the platinum group metals and a series of hydrometallurgical processes to separate and purify the individual platinum group metals including iridium.

15. The method according to any of the preceding claims, The membrane material coated with the spent catalyst is either a catalyst-coated membrane or one or more catalyst materials containing ionomers that have been separated from the ionomer membrane.

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