Recycling of catalyst coated membrane components

Abstract

A method of recycling a waste 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 comprising: (a) treating the waste catalyst coated membrane material with a heated solution comprising an acid and an oxidant, wherein platinum, palladium and / or ruthenium is leached from the waste catalyst coated membrane material into the solution which is separated from remaining solid components of the waste catalyst coated membrane material; (b) treating the waste catalyst coated membrane 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 the platinum, palladium and / or ruthenium in step (a); and (c) after recovery of the platinum, palladium and / or ruthenium and ionomer in steps (a) and (b), treating the residual waste catalyst coated membrane material to extract iridium by one of three specified processes.

Description

[0001] RECYCLING OF CATALYST COATED MEMBRANE COMPONENTS

[0002] Field

[0003] This specification relates to recycling methods for components of catalyst coated membranes such as those used in fuel cells and hydrogen producing water electrolysers.

[0004] Background

[0005] Fuel cell and hydrogen producing water electrolyser production is set for rapid growth as investment is placed into the global hydrogen economy. Catalyst coated membranes (CCMs) are a major functional component of both fuel cells and electrolysers. Such CCMs generally comprise a conductive polymer membrane coated on either side by a catalyst containing layer. The CCMs are configured to drive oxidation and reduction reactions and support proton and electron transport, these processes being required for the fuel cell and electrolyser technologies to function.

[0006] While variations in CCM component materials and configurations exist according to functional performance requirements in end use applications, they generally contain several components of value including one or more platinum group metal (PGM) catalysts and one or more proton conducting polymers.

[0007] Typically, the membrane is formed of one or more ionomers such as perfluorosulfonic-acid (PFSA) ionomers. Ionomer may also be provided in one or both of the catalyst layers. The ionomer in the catalyst layers may be the same or different to the ionomer in the main membrane component and / or in the other catalyst layer(s).

[0008] A CCM may comprise two different catalysts, one for driving an oxidation reaction on one side of the CCM and one for driving a reduction reaction on the other side of the CCM. A CCM may also comprise a recombination catalyst which is provided to catalyse the recombination of hydrogen and oxygen to form water, reducing the quantity of hydrogen crossing the membrane and mixing with oxygen to form a potentially explosive mixture. A CCM may also include a metal oxide (e.g., CeCh) as a peroxide scavenger.

[0009] CCM catalysts can be based on platinum group metals such as platinum, ruthenium, iridium, palladium, or mixtures thereof. The platinum group metals may be provided in elemental (metallic) form, in compound form (e.g., an oxide, such as an iridium oxide catalyst), or as a PGM-base metal alloy (e.g., PtCo). Furthermore, the PGM catalyst materials may be supported on a substrate material (e.g., carbon, such as a platinum-on-carbon catalyst comprising particles of carbon on which platinum is disposed or PtCo-on-carbon).

[0010] Catalyst coated membranes (CCMs) can also be provided in combination with additional functional layers to form multi-layer membrane electrode assemblies (MEAs). Such MEAs may have 3, 5, or 7 layers for example.

[0011] With the increase in CCM manufacture for fuel cells and electrolysers, there is an associated increase in CCM waste materials, including a significant volume of scrap material created during CCM manufacture (e.g., due to failure at quality control) and also an increase in end-of-life (EoL) CCMs. Since CCMs contain several components which are rare and / or valuable, including platinum group metals (notably Pt, Pd, Ir and Ru) and ionomer (both in the membrane and catalyst layers), there is a growing demand for methods of recycling such components from waste CCM materials.

[0012] One current method to recover PGMs from production scrap and end-of-life CCM material involves incineration. The incineration process yields a PGM rich (typically Pt and Ir) ash which 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 these gases have negative impacts as they pollute the atmosphere, increase the greenhouse effect, and / or have harmful effects in the human body. As such, there is a need for a cleaner process which reduces or eliminates the emission of these gases.

[0013] In addition to the above, the incineration method destroys the ionomer component which also has significant value. As such, it would also be desirable to provide a process which is capable of recovering both PGM and ionomer components as well as providing a process which is cleaner, safer, and more environmentally friendly. Processes for recovering perfluorosulphonic acid ionomer are known. See, for example, WO2016 / 156815 and US7255798. Furthermore, processes for recovering individual PGM catalyst components are known. See, for example, US7709135. However, to enable fuel cells and electrolysers to become more sustainable technologies, there is a need for commercially viable and environmentally friendly routes to recover, separate, and recycle both the PGMs and the ionomer components from waste CCM materials including production scrap and end-of-life material.

[0014] It is an aim of the present specification to address this problem.

[0015] Summary of Invention

[0016] The present specification is particularly concerned with the recycling of waste catalyst coated membrane materials which comprise an ionomer, at least one catalyst comprising platinum, palladium and / or ruthenium, and at least one catalyst comprising an iridium binary oxide such as iridium tantalum oxide (IrTaOx) and / or iridium ruthenium oxide (IrRuOx). Iridium binary oxides present a particular challenge as they are notoriously stable catalysts and are therefore resistant to simple acid dissolution and purification methods which may be used for other catalyst materials. The present specification provides a method which is capable of recovering all the platinum group metal components as well as the ionomer components from waste catalyst coated membrane materials comprising iridium binary oxides such as iridium tantalum oxide (IrTaOx) and / or iridium ruthenium oxide (IrRuOx).

[0017] According to the present specification there is provided a method of recycling a waste 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 (e.g., IrTaOx and / or IrRuOx), the method comprising:

[0018] (a) treating the waste catalyst coated membrane material with a solution comprising an acid and an oxidant, wherein platinum, palladium and / or ruthenium is leached from the waste catalyst coated membrane material into the solution which is separated from remaining solid components of the waste catalyst coated membrane material;

[0019] (b) treating the waste catalyst coated membrane 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 the platinum, palladium and / or ruthenium in step (a); and (c) after recovery of the platinum, palladium and / or ruthenium and ionomer in steps (a) and (b), treating the residual waste catalyst coated membrane material to extract iridium by one of the following three processes:

[0020] (i) directly recovering the iridium as solid iridium binary oxide catalyst material after the leaching of the platinum, palladium and / or ruthenium and the dispersion and recovery of the ionomer;

[0021] (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 an acid dissolve to recover the iridium in solution;

[0022] (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 the individual platinum group metals including iridium.

[0023] The methodology is based on the realization that since the iridium binary oxide component is the most stable component it is advantageously recovered after recovery of the platinum, palladium and / or ruthenium component and the ionomer component. In this regard, it has been found that the iridium binary oxide component is not leached by leaching processes which can be utilized to recover the platinum, palladium and / or ruthenium component. Furthermore, the iridium binary oxide component has been found to meet specification requirements for re-use in fuel cell applications after being subjected to oxidative acid leaching conditions used for recovery of the platinum, palladium and / or ruthenium component(s). As such, according to route (c)(i) of the present method, it is possible to recover the iridium binary oxide catalyst material for direct re-use rather than requiring metal separation, purification, and re-synthesis of a new iridium binary oxide catalyst material.

[0024] As an alternative to direct recovery and re-use of the iridium binary oxide catalyst material, it is possible to recover the iridium component of the binary oxide material. However, while a reductive acid leach can be used to recover iridium from non-binary iridium oxide catalyst materials, such a reductive acid leaching process does not give a high yield of iridium recovery for iridium binary oxide catalyst materials. According to the present specification, two alternatives are available in addition to the direct recovery route (c)(i).

[0025] According to route (c)(ii), the iridium binary oxide is subjected 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 an acid dissolve to recover the iridium in solution. Peroxide fusion processes are already currently carried out by analytical labs to assay iridium binary oxide materials. In the present specification, this known methodology is transferred from an analytical analysis context to a recycling methodology for recovery of iridium (and optionally the other metal component of the binary oxide) from waste iridium binary oxide materials generated after separation of platinum and ionomer components.

[0026] Alternatively, according to route (c)(iii), the iridium binary oxide can be fed into a PGM refining circuit where the material 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. Optionally, the residual iridium binary oxide containing material can be ashed to remove any residual ionomer before entering the refining circuit. Advantageously, this approach can use existing PGM refining processes to separate and purify iridium (and optionally the other metal component of the binary oxide) from waste iridium binary oxide materials generated after separation of platinum and ionomer components. However, recycling times may be longer when compared to the more bespoke recycling approaches of routes c(i) and c(ii).

[0027] Further details of the methodology are provided in the detailed description below.

[0028] Brief Description of the Drawings

[0029] For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawing, in which:

[0030] Figure 1 shows a waste CCM recycling process according to the present specification;

[0031] Figure 2 shows FTIR data for fluorinated polymer membrane material, fluorinated polymer salt material formed after treatment in water and base, and fluorinated polymer salt material formed after treatment in water and base followed by a water wash;

[0032] Figure 3 shows an example of process steps (pre-autoclave) including refluxing fluorinated polymer membrane in a basic LiOH solution to form a fluorinated polymer salt without dispersing the membrane followed by washing with water;

[0033] Figure 4 is a photograph showing the membrane before (left hand side) and after (right hand side) the process steps of refluxing the membrane in a basic LiOH solution and washing with water;

[0034] Figure 5 shows a further step of autoclaving the membrane following the treatment process as shown in Figure 3 to disperse the membrane in water; and

[0035] Figure 6 shows a further step (post-autoclave) of ion exchange to convert the dispersed polymer salt back to protonated acid form.

[0036] Detailed Description

[0037] As described in the summary section and illustrated in Figure 1, according to one aspect of the present specification there is provided a method of recycling a waste 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 (e.g., IrTaOx and / or IrRuOx), the method comprising:

[0038] (a) treating the waste catalyst coated membrane material with a solution comprising an acid and an oxidant, wherein platinum, palladium and / or ruthenium is leached from the waste catalyst coated membrane material into the solution which is separated from remaining solid components of the waste catalyst coated membrane material;

[0039] (b) treating the waste catalyst coated membrane 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 the platinum, palladium and / or ruthenium in step (a); and (c) after recovery of the platinum, palladium and / or ruthenium and ionomer in steps (a) and (b), treating the residual waste catalyst coated membrane material to extract iridium by one of the following three processes:

[0040] (i) directly recovering the iridium as solid iridium binary oxide catalyst material after the leaching of the platinum, palladium and / or ruthenium and the dispersion and recovery of the ionomer;

[0041] (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 an acid dissolve to recover the iridium in solution;

[0042] (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 the individual platinum group metals including iridium.

[0043] In step (a), the acid used in the leach of platinum, palladium and / or ruthenium can be hydrochloric acid. The oxidant used for the leach can be a chlorate salt, chlorine gas, or hydrogen peroxide. The oxidant concentration can be: at least 0.001, 0.005, or 0.01 mol / l; no more than 1, 0.5, or 0.10 mol / l; or within a range defined by any combination of the aforementioned lower and upper limits (e.g., in a range 0.01 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 aforementioned lower and upper limits. The leaching 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 aforementioned lower and upper limits, wherein if the solution is heated above 100°C then this is done in a pressurized vessel.

[0044] These leaching conditions have been found to be effective at leaching platinum, palladium and / or ruthenium catalyst material. Furthermore, these leaching conditions do not leach any of the iridium binary oxide. The effects of the leaching process on the microstructure, crystallography, and composition of the iridium binary oxide are minor and the iridium binary oxide remains in a form that can be directly re-used to make new CCM components.

[0045] As specified in step (b) of the method, either before or after the aforementioned leaching step, the ionomer is dispersed, and the resultant ionomer dispersion is separated from the remaining waste catalyst coated membrane material including the iridium binary oxide. The solvent used to disperse the ionomer can be selected from water, an aqueous basic 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 aforementioned lower and upper limits. The heating can be performed in an autoclave.

[0046] According to certain preferred methods, the ionomer can be treated with a base (e.g., an aqueous solution of a metal hydroxide or ammonium hydroxide, such as LiOH) to convert the ionomer to salt form. The treatment can be performed on solid ionomer material without dispersing the solid ionomer material so long as the material is not heated up to the aforementioned temperatures for the dispersal step. The excess base can then be removed and replaced with another solvent (e.g., water) prior to dispersing the ionomer in the solvent by heating in an autoclave as previously described. Alternatively, the aqueous basic solution can be used as the solvent in which the ionomer is dispersed by heating. However, one advantage of converting the solid ionomer to salt form first and then subsequently dispersing the ionomer in a different solvent is that the excess base can be removed prior to ionomer dispersion such that the ionomer dispersion is not contaminated with excess base.

[0047] Once the ionomer and platinum, palladium and / or ruthenium catalyst material has been removed, the residual waste catalyst coated membrane material comprises the iridium binary oxide and potentially other components such as carbon and / or membrane reinforcement material. Advantageous, the iridium binary oxide is separated from any other residual components prior to further processing. For example, a slurry of the residual waste material can be formed and filtered to separate solid components according to their different particle sizes. The recovered iridium binary oxide can then be washed and dried ready for re-use in a new catalyst ink formulation.

[0048] While it has been found that iridium binary oxide material can be directly recovered in an acceptable form to be re-used in this manner, if the recovered binary oxide material does not meet specifications for a particular application, or recovery of individual metal components is desired, the individual metal components can be separately recovered and purified instead. According to route (c)(ii) of the method, the iridium binary oxide is subjected 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 an acid dissolve to recover the iridium in solution. The other metal in the binary oxide (e.g., Ta or Ru) can also be recovered via this route.

[0049] Alternatively, the 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 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. The other metal in the binary oxide (e.g., Ta or Ru) can also be recovered via this route.

[0050] The methodology as described herein can be applied to waste catalyst coated membrane material in the form of a catalyst coated membrane or in the form of ionomer containing catalyst materials which have been separated from an ionomer membrane.

[0051] Examples

[0052] Platinum Recovery

[0053] CCM - HCI / Chlorate Leach

[0054] A method has been developed to leach PGMs from CCM production scrap. The recovered PGM material is subsequently refined using existing PGM refining processes. For such processes, there are stringent limits on the fluorine content (<1%) of the PGM material introduced into PGM refining processes. This was identified as a potential issue for leaching PGMs from waste CCM materials, as the CCMs are predominantly made from fluoropolymer. The present leaching process is such that PGMs can be leached without also introducing significant quantities of fluorine into the leach liquor.

[0055] A HCI / Chlorate solution was used to dissolve the Pt from the CCM. Ir is in the oxide form in the CCM and no significant quantity of the Ir is leached, enabling a separation of Pt and Ir. Chlorate was introduced in the form of a sodium chlorate solution added using a peristaltic pump.

[0056] A vessel was charged with a fuel cell CCM (cut into approximately 2 cm x 3 cm pieces). 400 mL of 6M HCI (solution made from concentrated HCI and distilled H2O) was charged to the flask and the stirring speed was set to 250 rpm. The reaction mixture was heated to 70°C. During heating a slight yellow colour to the solution could be seen. 4 mL of NaCIOs solution (450g / L) was added at a rate of approximately 0.09 mL / min. After addition of NaCIOs solution had finished, the reaction mixture was cooled to room temperature. The reaction mixture was filtered through 0.45 pm filter paper which gave a yellow solution (365 mL). The liquor was collected, and the residual CCM pieces were washed with distilled H2O (86 mL). The CCM pieces were picked out and laid out to dry in air overnight on a watch glass.

[0057] IC / ICP analysis indicated that the leach conditions do not leach the Ir to any significant extent. In contrast, approximately 100% of the Pt was leached into the leach liquor. The liquor also showed undetectable amounts of fluoride, indicating the leach conditions are not destructive to the ionomer in the CCM.

[0058] As such, it has been shown that this approach can be used for recovery of Pt from waste CCM material without damaging the ionomer material of the CCM or introducing fluorine into the Pt processing stream for subsequent Pt refining. It has also been shown that the Pt can be leached from waste CCM material without also leaching iridium, thus enabling Pt and Ir to be separated and recovered for reuse. As such, using this approach it is possible to recover the Pt, Ir, and ionomer components (and optionally ruthenium or palladium if present).

[0059] Ionomer Recovery

[0060] Perfluorosulfonic-acid ionomer membrane pieces were cut into sufficiently small pieces to fit in a vessel. 6.0 g of anhydrous LiOH and 250 g of water were weighed and the LiOH dissolved in the water. The membrane pieces were submerged in the LiOH solution and heated to reflux for 1 hour. The resultant mixture was washed out with 4 X 100 mL of water. The remaining water was decanted to leave (wet) membrane pieces. 250 g of water was weighed, added to the (wet) membrane pieces, and heated to reflux for 1 hour. The water was then decanted off and the solid product dried under vacuum.

[0061] Figure 2 shows FTIR data showing salt formation. FTIR data was collected for untreated fluorinated polymer membrane material 301, fluorinated polymer salt material formed after treatment in the aqueous solution of LiOH 303, and fluorinated polymer salt material formed after treatment in the aqueous solution of LiOH followed by the water wash 304.

[0062] Figure 3 shows an example of process steps (pre-autoclave). Membrane on a roll was cut and then further cut or folded to size. The membrane was brown in colouration as indicated in the figure. The membrane was then refluxed in a solution of lithium hydroxide wherein the membrane turned colourless and converted to salt form as confirmed by spectroscopic analysis. The conversion was achieved without dispersing the membrane which remained in solid, undispersed form.

[0063] It may be noted that the colour change of the membrane is not necessarily indicative of the chemical change and membranes can have different colours. However, in the illustrative examples the chemical change of the polymer from protonated to salt form was accompanied by an associated colour change as shown in the figures.

[0064] In the final step of the pre-autoclave process shown in Figure 3, the solid polymer salt membrane material was washed in water to remove any residual LiOH solution. Figure 4 is a photograph showing the membrane before (left hand side) and after (right hand side) the process steps of refluxing the membrane in a basic LiOH solution and washing with water indicating the colour change of the membrane from brown to colourless and the fact that the membrane remained in solid, undispersed form. Spectroscopic analysis confirmed that the colourless membrane was in salt form. Figure 5 shows a further step of autoclaving the membrane following the treatment process as shown in Figure 3 to disperse the membrane in water. The colourless, solid, undispersed, polymer salt membrane was autoclaved in water under nitrogen at 250°C and 40 bar (4000 kPa) pressure. This resulted in a (non-basic) aqueous dispersion of the polymer salt.

[0065] Figure 6 shows a further step (post-autoclave) of ion exchange to convert the dispersed polymer salt back to protonated acid form. An ion exchange column containing Amberlyst™ 15 (H) resin was utilized for this process step. The dispersion of (protonated) fluorinated polymer may be re-used to manufacture new membranes or dried and stored for future use.

[0066] Iridium Recovery

[0067] IrTaOx is found in certain catalyst powders for fuel cell applications in order to increase stability of the system. However, oxidative leaching experiments using peroxide and NaCIOs have shown a 0% Ir recovery when leaching IrTaOx. This offers a possibility for direct recovery and reuse of IrTaOx as a catalyst powder.

[0068] To understand if the leached residue can be recycled directly, powder characterisation has been carried out and compared to the starting material to see how the leaching conditions have affected the material structure. If the structure is not changed significantly then it can be recycled, optionally blending with new material.

[0069] To test whether iridium binary oxides can be directly recycled and re-used as catalyst material in fuel cell catalyst coated membranes using the methodology as described herein, samples of material have been subjected to oxidative acid leaching processes as used to recover the platinum (or alternatively palladium or ruthenium). The samples of solid iridium binary oxide material recovered after the platinum leaching process have then been analysed using SEM, XRD, ICP, and nitrogen BET surface area measurements to determine whether they meet specifications for re-use as catalyst in new fuel cell catalyst coated membranes. To determine if there is any variation according to the specific leaching process used for recovery of the platinum, one set of samples was subjected to a HCI acid leach using peroxide as the oxidant and another set of samples was subjected to a HCI acid leach using NaCIOs as the oxidant.

[0070] SEM Analysis

[0071] SEM images were taken of iridium tantalum oxide starting material. Further SEM images were taken of iridium tantalum oxide after being subjected to an HCI acid leach using H2O2 as the oxidant. Yet further SEM images were taken of iridium tantalum oxide after being subjected to an HCI acid leach using NaCIOs as the oxidant.

[0072] Visual inspection of the SEM images suggested the particles were more broken up and / or had a smaller particle size when using NaCIOs as the oxidising agent. This suggests NaCIOs is a harsher oxidising agent than peroxide. The images of the starting material compared to the sample leached with peroxide appear to be more similar in structure suggesting peroxide does not damage the structure as much and could be better for direct recycle.

[0073] After analysing the SEM data, it was decided more IrTaOx would be leached using HCI / NaCIOs since visually, from the SEM analysis, this sample had more differences compared to the starting material, so would more likely benefit from the data collected in the QC analysis. Using NaCIOs as the oxidant is also more similar to the conditions used with CL (g) which is more likely to be used as the oxidant when the process is run at larger scale. XRD Analysis

[0074] XRD analysis of a leached sample with NaCIOs showed the phase was Ir / Ta oxide and the single crystalline phase determined by XRD is within product specifications with respect to average crystallite size and composition for the IrTaOx catalyst material.

[0075] ICP Analysis

[0076] Leached residue was sent for ICP analysis with results showing Ir and Ta content which lie within the specifications for the IrTaOx catalyst material. The impurities in the sample are also within the specification limits. The Fe content is also lower than the specified limit, as is the Cl content. Overall, the leached samples pass the specification criteria for ICP results.

[0077] Nitrogen BET Analysis

[0078] The BET surface area was measured and also lies within the specification limits for the IrTaOx catalyst material, so the leached material has passed on this criterion too.

[0079] Conclusion

[0080] Trials with IrTaOx powder have shown the material still meets product specification after exposing catalyst to Pt leaching processes. Results indicate that a direct recycling route for iridium binary oxide material is viable.

[0081] Peroxide Fusion

[0082] As an alternative to direct recovery and re-use of the iridium binary oxide catalyst material, the iridium and other metal can be recovered using a peroxide fusion process. Peroxide fusion is already used to process samples of iridium binary oxide catalyst powders for analysis. The iridium binary oxide catalyst powders are mixed with an alkali fusion flux, heated in a furnace, and then subjected to an acid dissolve to recover the iridium in solution. The other metal in the binary oxide (e.g., Ta or Ru) can also be recovered via this route. For example, an iridium binary oxide can be mixed with sodium peroxide, heated in a furnace, and then acid leached. Examples of such a method for the processing of iridium are 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, volume 52 (2011) Issue 11. This paper describes the dissolution of iridium with an alkali fusion treatment with NajCh followed by leaching in HCI solution. It is described that alkali fusion with Na2O2 allows Ir to be easily oxidized to IrCh, which is transformed to a high oxidation state through the binding of Na-lr-0 at 600°C for 4 h. From the fused mixture, with molar ratio of 1:2.0 (lr:Na2O2), Ir can be leached completely at 130°C using an HCI solution with a concentration above 3 M. Moreover, the leaching with 3 M HCI at 130°C can dissolve Ir from the mixture that was fused at 600°C, regardless of molar ratio of Na2O2. Ir can also be completely dissolved at 70°C or less when the fused mixture has a 1:2.0 ratio. In accordance with the present specification, a corresponding process can be used for recovery of iridium from iridium binary oxide catalyst powders used in CCMs. However, in the case of an IrTaOx catalyst, the use of HF in addition to HCI is required to support separation of tantalum.

[0083] Large scale fusion is already used for processing materials. As such, this representative a viable alternative route for recovering iridium (as well as the other metal in the binary oxide).

[0084] Pyrometallurgical Route

[0085] As an alternative to using the peroxide fusion method as described above, the iridium binary oxide material can be supplied into an existing PGM refining process involving pyrometallurgical processing followed by acid dissolve and hydrometallurgical separation and purification of PGMs. The pyrometallurgical route may require an ashing step to burn off residual ionomer before entering an existing refining circuit to follow existing processes for refining PGM feeds. For example, material can be smelted at over 1200°C for around 12 hours in reverberatory furnaces to separate the non-metallic components and produce an iron-based feed which contains the PGMs. The bullion feed undergoes acid leaching to concentrate the PGMs into solution, followed by a series of solvent extractions, evaporation, precipitation and filtration steps to separate and purify the PGMs.

[0086] Summary

[0087] The present specification provides a flow sheet to recover Pt (or alternatively Pd or Ru), ionomer, and IrTaOx (as well as alternative Ir binary oxides) from fuel cell membrane electrode assemblies (MEAs) and catalyst coated membranes (CCMs). The Pt can be recovered by an oxidative leach using HCI as the acid with chlorine, hydrogen peroxide, or sodium chlorate as the oxidant. The remaining residue then undergoes an ionomer dispersion process, although it should be noted that the ionomer recovery and Pt recovery can occur in either order. The remaining residue contains mainly IrTa oxide or an alternative binary oxide such as IrRu oxide and some carbon. This can then undergo a selection of recovery methods. One route is to employ separation techniques to directly recover the IrTaOx as a catalyst powder, ready for reuse. Alternatively, the residue can undergo a peroxide fusion process, currently carried out by analytical labs to assay this material and barium peroxide fusions are already carried out at scale. This will allow the Ir to enter solution and can then be processed using known techniques to purify the material. Another option is to allow this material to enter an existing refining circuit so that it follows a pyrometallurgical route. The residue can be ashed before entering the refining circuit.

[0088] This specification thus allows for the recovery of all PGMs and ionomer in waste CCM materials which comprise iridium binary oxides such as IrTaOx.

[0089] While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Claims1. A method of recycling a waste 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 comprising:(a) treating the waste catalyst coated membrane material with a solution comprising an acid and an oxidant, wherein platinum, palladium and / or ruthenium is leached from the waste catalyst coated membrane material into the solution which is separated from remaining solid components of the waste catalyst coated membrane material;(b) treating the waste catalyst coated membrane 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 the platinum, palladium and / or ruthenium in step (a); and(c) after recovery of the platinum, palladium and / or ruthenium and ionomer in steps (a) and (b), treating the residual waste catalyst coated membrane material to extract iridium by one of the following three processes:(i) directly recovering the iridium as solid iridium binary oxide catalyst material after the leaching of the platinum, palladium and / or ruthenium and the dispersion and recovery of the ionomer;(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 an acid dissolve to recover the iridium in 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 the individual platinum group metals including iridium.

2. A method according to claim 1, wherein the iridium binary oxide is iridium tantalum oxide or iridium ruthenium oxide.

3. A method according to claim 1 or 2, wherein, in step (a), the acid used in the leach of platinum, palladium and / or ruthenium is hydrochloric acid.

4. A method according to any preceding claim, wherein, in step (a), the oxidant used for the leach of platinum, palladium and / or ruthenium comprises a chlorate salt, chlorine gas, or hydrogen peroxide.

5. A method according to any preceding claim, wherein, in step (a), the solution for leaching platinum, palladium and / or ruthenium has an oxidant concentration of: at least 0.001, 0.005, or 0.01 mol / l; no more than 1, 0.5, or 0.10 mol / l; or within a range defined by any combination of the aforementioned lower and upper limits.

6. A method according to any preceding claim, wherein, in step (a), the solution for leaching platinum, palladium and / or ruthenium has an acid concentration of: 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 aforementioned lower and upper limits.

7. A method according to any preceding claim, wherein, in step (a), the solution used for the leach of platinum, palladium and / or ruthenium is 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 aforementioned lower and upper limits, wherein if the solution is heated above 100°C then this is done in a pressurized vessel.

8. A method according to any preceding claim, wherein, in step (b), the solvent used to disperse the ionomer is selected from water, an aqueous basic solution, an organic solvent, an alcohol, or a mixture of an alcohol and water.

9. A method according to any preceding claim, wherein, in step (b), the solvent used to disperse the ionomer is 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 aforementioned lower and upper limits.

10. A method according to any preceding claim, wherein, in step (b), the ionomer is treated with a base to convert the ionomer to salt form prior to dispersing the ionomer in the solvent.

11. A method according to any preceding claim, wherein, in step (c), the solid iridium binary oxide catalyst material is separated from other residual components of the waste catalyst coated membrane material by formation of a particulate suspension and filtration to separate components by particle size.

12. A method according to any preceding claim,wherein, in step (c), the iridium is recovered via route (i) in which the iridium is directly recovered as 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. A method according to any one of claims 1 to 11, wherein, in step (c), the iridium is recovered via route (ii) in which the iridium binary oxide is subjected 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 an acid dissolve to recover the iridium in solution.

14. A method according to any one of claims 1 to 11, wherein, 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. A method according to any preceding claim, wherein the waste catalyst coated membrane material is a catalyst coated membrane or one or more ionomer containing catalyst materials which have been separated from an ionomer membrane.

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