Recycling of catalyst coated membrane components

Abstract

A method of recycling a waste catalyst coated membrane material comprising an ionomer membrane, a catalyst comprising iridium and a catalyst comprising at least one of platinum, palladium and / or ruthe

Description

Field This specification relates to recycling methods for components of catalyst coated membranes such as those used in fuel cells and hydrogen producing water electrolysers. Background 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 been required for the fuel cell and electrolyser technologies to function. 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. 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). 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. 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). 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. 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. 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. 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. It is an aim of the present specification to address this problem. Summary of Invention The present inventors have considered methodologies for recycling waste catalyst coated membrane materials comprising an ionomer membrane, at least one catalyst comprising platinum, palladium and / or ruthenium, and at least one catalyst comprising iridium. The present inventors have considered recovering the ionomer via a solvent dispersal process, recovering the iridium using a leaching process, and recovering the platinum, palladium and / or ruthenium using another, different leaching process. It has been found that a reductive acid leaching process can be used to leach iridium, but the process also leaches a proportion of the platinum (and / or palladium and / or ruthenium). While PGM refining processes can be used to subsequently separate the platinum and iridium, this requires additional processing steps. In contrast, it has been found that an oxidative acid leaching process can be used to leach platinum, palladium and / or ruthenium and this process does not leach significant amounts of iridium. As such, it has been found that it can be advantageous to apply an oxidative acid leach first to selectively leach the platinum, palladium and / or ruthenium followed by a reductive acid leach to leach the iridium after the platinum, palladium and / or ruthenium has been removed. In this way, the platinum, palladium and / or ruthenium and iridium can be separately recovered and purified for reuse in a more efficient manner. The present inventors have also considered processes in which the ionomer is recovered via a solvent dispersal step prior to leaching of the platinum and / or iridium. However, it has been found that performing such a solvent dispersal step in the presence of PGM catalyst material can cause degradation of the ionomer material. In contrast, it has been found that the oxidative and reductive acid leaching processes used to leach platinum and iridium do not lead to significant degradation of the ionomer material. As such, it can be advantageous to remove the PGM material first prior to dispersal and recovery of the ionomer. In light of the above, according to one aspect of the present specification there is provided a method of recycling a waste catalyst coated membrane material comprising an ionomer membrane, at least one catalyst comprising platinum, palladium and / or ruthenium (e.g., a platinum-on-carbon catalyst), and at least one catalyst comprising iridium (e.g., an iridium oxide catalyst), the method comprising: (a) treating the waste catalyst coated membrane material with a heated solution comprising an acid and an oxidant, wherein the 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) after step (a), leaching iridium from the waste catalyst coated membrane material using a heated solution comprising an acid and a reducing agent and separating the solution comprising the leached iridium from remaining solid components of the waste catalyst coated membrane material; and (c) after steps (a) and (b), treating the waste catalyst coated membrane material with a heated solvent to disperse the ionomer membrane and recover a dispersion of ionomer. It has been found that performing the aforementioned steps in the stated order, it is possible to separately recover the platinum (and / or palladium and / or ruthenium), iridium, and ionomer materials without significantly degrading the ionomer and ensuing that substantially all (e.g., at least 97%) of the PGMs are recovered with the platinum (and / or palladium and / or ruthenium) and iridium being separated upfront in the process. One advantage of the aforementioned process is that it achieves a high yield of recovery for platinum (and / or palladium and / or ruthenium) and iridium. Another advantage of the aforementioned process is that substantially no fluorine is leached out from the fluoropolymer membrane into the leachate during the oxidative and reductive leaches. This is advantageous for two reasons. First, the ionomer remains intact and can be recycled separately. Secondly, leaching of fluorine into the acidic leachates can lead to the formation of HF which can result in a serious environmental health and safety risk as well as damaging downstream processing equipment. As such, avoiding HF formation provides a safer and more environmentally friendly process. Yet another advantage of the aforementioned process is that for CCMs which comprise both a platinum and an iridium oxide catalyst, which is a useful combination of catalysts for the cathode and anode catalysts respectively of a hydrogen producing water electrolyser, the oxidative leach conditions are selective for platinum and do not leach iridium to any significant extent. As such, the process step order represents an efficient way to separate platinum and iridium from the other components of such a waste CCM while leaving remaining CCM components intact to be processed separately. Yet another advantage is that the PGM material is removed prior to dispersal of the ionomer which avoids PGM driven degradation of the ionomer material during the ionomer dispersal step. In one preferred methodology, the ionomer is treated with a base to convert the ionomer to salt form prior to dispersing the ionomer in the solvent. Subsequently, after dispersal of the ionomer, the ionomer dispersion can then be subjected to an ion exchange process to re-protonate the ionomer in the dispersion. It has been found that this methodology is advantageous to achieve good dispersion of the ionomer material without damaging the ionomer material so long as the PGM material is removed prior to the ionomer dispersal process. As such, a preferred process flow is as follows: (i) oxidative acid leach to recover platinum (and / or palladium and / or ruthenium); (ii) reductive acid leach to recover iridium; (iii) treatment of remaining solid ionomer material with a base to form a solid ionomer salt material; (iv) heating the solid ionomer salt material in a solvent to disperse and recover the ionomer material; and (v) subjecting the ionomer dispersion to an ion exchange process to reprotonate the ionomer material. Brief Description of the Drawings 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 drawings, in which: Figure 1 shows a waste CCM recycling process comprising a platinum leach followed by an iridium leach followed by ionomer dispersion; Figure 2 shows a waste CCM recycling process comprising the following steps in the stated order: (i) oxidative acid leach to recover platinum; (ii) reductive acid leach to recover iridium; (iii) treatment of remaining solid ionomer material with a base to form a solid ionomer salt material; (iv) heating the solid ionomer salt material in a solvent to disperse and recover the ionomer material; and (v) subjecting the ionomer dispersion to an ion exchange process to re-protonate the ionomer material; Figure 3 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; Figure 4 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; Figure 5 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; Figure 6 shows a further step of autoclaving the membrane following the treatment process as shown in Figure 3 to disperse the membrane in water; Figure 7 shows a further step (post-autoclave) of ion exchange to convert the dispersed polymer salt back to protonated acid form; Figure 8 shows 19F NMR of ionomer dispersion from Pt-leached CCM without any significant degradation products; Figure 9 shows 19F NMR of ionomer dispersion from CCM containing Pt indicating PFAS degradation products; and Figure 10 shows 19F NMR of ionomer dispersion from membrane with a Pt recombination layer indicating PFAS degradation products. Detailed Description 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 membrane, at least one catalyst comprising platinum, palladium, and / or ruthenium (e.g., a platinum-on-carbon catalyst), and at least one catalyst comprising iridium (e.g., an iridium oxide catalyst), the method comprising: (a) treating the waste catalyst coated membrane material with a heated solution comprising an acid and an oxidant, wherein the platinum, palladium, and / or ruthenium (hereinafter generally referred to as platinum for brevity) 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) after step (a), leaching iridium from the waste catalyst coated membrane material using a heated solution comprising an acid and a reducing agent and separating the solution comprising the leached iridium from remaining solid components of the waste catalyst coated membrane material; and (c) after steps (a) and (b), treating the waste catalyst coated membrane material with a heated solvent to disperse the ionomer membrane and recover a dispersion of ionomer. It has been found that performing the aforementioned steps in the stated order, it is possible to separately recover the platinum, iridium, and ionomer materials without significant degrading the ionomer and ensuing that substantially all (e.g., at least 97%) of the PGMs are recovered with the platinum and iridium being separated upfront in the process. The acid used in one or both of the iridium leach and the platinum leach is preferably hydrochloric acid and optionally does not contain nitric acid. Furthermore, one or both of the solution used for the leach of platinum and the solution used for the leach of iridium are preferably heated to a temperature of: at least 50°C, 60°C, or 70°C; no more than 160°C, 120°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. Example temperatures are around 70°C for the platinum leach and around 105°C for the iridium leach. Solutions are heated to increase leaching rate of PGMs. The oxidant can comprise, for example, a halide salt, optionally a chlorate salt such as sodium chlorate solution, hydrogen peroxide, or chlorine gas. According to one preferred option, the acid used in the leach of platinum, palladium and / or ruthenium is hydrochloric acid and the oxidant is chlorine gas generated from the hydrochloric acid electrolytically in-situ. The oxidant can be added to the hydrochloric acid solution or generated in-situ after heating up to the aforementioned temperature. Alternatively, the oxidant can be added in a plurality of aliquots during heating. For example, oxidant can be added in a series of aliquots during heating. The solution for leaching platinum may have 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 (e.g., a total oxidant concentration in a range 0.01 to 0.10 mol / l). One or both of the solution used for the leach of platinum and the solution used for the leach of iridium has an acid concentration of: no less than 4 M, 5 M, 5.5 M, or 6 M; no more than 15 M, 12 M, 10 M, or 7 M; or within a range defined by any combination of the aforementioned lower and upper limits. Separation of the solution containing the leached platinum may be achieved via filtration or centrifugation. The separated solution may be concentrated by boiling the solution down to a suitable platinum concentration for further processing. Alternatively, the leachate can be recirculated to leach platinum from further waste catalyst coated membrane material, recirculation being repeated as required until a suitable or target concentration of platinum is reached. For example, after separating the solution containing the leached platinum from remaining solid components of the waste catalyst coated membrane material, the solution can be concentrated to yield chloroplatinic acid comprising at least 30 wt% Pt. One advantage of the aforementioned process is that it achieves a high yield of recovery for platinum, palladium and / or ruthenium. For example, at least 97wt% of the platinum in waste catalyst coated membrane can be recovered. Another advantage of the aforementioned process is that substantially no fluorine is leached out from the fluoropolymer membrane into the leachate using these conditions. This is advantageous for two reasons. First, the ionomer remains intact and can be recycled separately. Secondly, leaching of fluorine into the acidic leachate can lead to the formation of HF which can result in a serious environmental health and safety risk as well as damaging downstream processing equipment. As such, avoiding HF formation provides a safer and more environmentally friendly process. Yet another advantage of the aforementioned process is that for CCMs which comprise both a platinum and an iridium oxide catalyst, which is a useful combination of catalysts for the cathode and anode catalysts respectively of a hydrogen producing water electrolyser, the leach conditions are selective for platinum and do not leach iridium to any significant extent. As such, the process represents an efficient way to separate platinum from the other components of such a waste CCM while leaving remaining CCM components intact to be processed separately. The iridium (which may be in the form of an iridium oxide, mixed iridium oxide, or supported iridium oxide) can be separately extracted using an acid leaching process. This differs from that used for leaching of platinum. In particular, a reducing agent (e.g., hydrazine) rather than an oxidizing agent is used for the iridium leach. Optionally, the reducing agent is added to the waste catalyst coated membrane material first and then followed by addition of the acid. The solution for leaching iridium may have a reducing agent concentration of: at least 1 wt%, 3 wt%, or 5 wt%; no more than 35wt%, 30 wt%, 20 wt%, 10 wt%, or 7.5 wt%; or within a range defined by any combination of the aforementioned lower and upper limits. One advantage of the aforementioned process is that it achieves a high yield of recovery for iridium. For example, at least 95wt% of the iridium in waste catalyst coated membrane can be recovered. Another advantage of the aforementioned process is that substantially no fluorine is leached out from the fluoropolymer membrane into the leachate using these conditions. This is advantageous for two reasons. First, the ionomer remains intact and can be recycled separately. Secondly, leaching of fluorine into the acidic leachate can lead to the formation of HF which can result in a serious environmental health and safety risk as well as damaging downstream processing equipment. As such, avoiding HF formation provides a safer and more environmentally friendly process. As previously indicated, the iridium leaching conditions are such that they do also leach a significant quantity of platinum (e.g., 20 - 40% of the Pt) if still present in the waste catalyst coated membrane material. As such, in accordance with the present methodology the Pt is removed first by oxidative leaching prior to applying the reductive leach to recover the iridium. After the platinum and iridium have been recovered from the waste catalyst coated membrane, it can be treated with a heated solvent to disperse the ionomer membrane and recover a dispersion of ionomer. 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. The solvent used to disperse the ionomer 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. In one preferred methodology, the ionomer is treated with a base to convert the ionomer to salt form prior to dispersing the ionomer in the solvent. Subsequently, after dispersal of the ionomer, the ionomer dispersion can then be subjected to an ion exchange process to re-protonate the ionomer in the dispersion. It has been found that this methodology is advantageous to achieve good dispersion of the ionomer material without damaging the ionomer material so long as the PGM material is removed prior to the ionomer dispersal process. As such, a preferred process flow as illustrated in Figure 2 is as follows: (i) oxidative acid leach to recover platinum; (ii) reductive acid leach to recover iridium; (iii) treatment of remaining solid ionomer material with a base to form a solid ionomer salt material; (iv) heating the solid ionomer salt material in a solvent to disperse and recover the ionomer material; and (v) subjecting the ionomer dispersion to an ion exchange process to re-protonate the ionomer material. Examples PGM recovery For water electrolyser materials, Ir has been recovered via a reductive leach, but these have shown varying levels of Pt recovery at the same time. In order to minimise this mixing of Pt and Ir chloride species, the Pt oxidative leach has been trialled first, followed by the reductive Ir leach. For reliability, this experiment has been repeated twice. Pt oxidative leach Five water electrolyser CCMs were shredded into pieces of 1 cm x 2 cm size. Total CCM mass was 21.23 g. A flange vessel equipped with an overhead stirrer, condenser with cooling water, temperature probe and stoppers in all vacant ports was set up on a hot plate. This was loaded with the CCMs and 395 mL 12M HCI added to it, with the solution yellowing immediately. This was set to stir at 200 rpm and the heat set to 70°C. When at temperature, 1.25 mL 30% peroxide was added to the vessel via a Watson Marlow peristaltic pump at 1 rpm for the first minute and then at 7 rpm for the remainder of the addition. This reaction was left heating for a further 50 minutes. Once complete, the heat was turned off and the reaction allowed to cool. This was filtered under vacuum with cellulose nitrate filter paper. Ir reductive leach The leached CCMs were suspended in 90 mL demineralized water in a beaker and 1.8 mL 35% hydrazine added dropwise whilst stirring. The CCMs greyed where in contact with hydrazine directly. This suspension was sonicated in an ultrasonic bath at room temperature for 5 minutes. The flange vessel was set up as before with the Pt leach. The CCM suspension was added to the flange vessel. 250 mL 12M HCI was added slowly, in increments, whilst stirring at 200 rpm. The CCM pieces began to break apart at this point. A sample was taken. The vessel was heated to 105°C. When at temperature, the timer was started and a sample taken every 1.5 hours for a total of 4.5 hours. After this, the reaction vessel was cooled and the suspension filtered via a vacuum. All samples were filtered under vacuum and then syringe filtered. Pt oxidative leach (repeated) The repeat experiment used the same method for the oxidative leach but removed the sonication step for the reductive leach. Mass of CCMs was 21.27 g, 400mL of 12M acid was used, heating was to 75 °C, and 1.5 mL of hydrogen peroxide was used. As before, heating was performed for 50 minutes. Ir reductive leach (repeated) The flange vessel was set up as before. The CCMs were added to the vessel with 90 mL demineralized water. This was set to stir at 130 rpm whilst 1.8 mL hydrazine was added dropwise. This was left to stir for 5 minutes. 250 mL of 12M HCI was added slowly whilst stirring at 300 rpm. As before, the vessel was heated to 105°C. When at temperature, the timer was started and a sample taken every 1.5 hours for a total of 4.5 hours. After this, the reaction vessel was cooled and the suspension filtered via a vacuum. All samples were filtered under vacuum and then syringe filtered. Results Discussion and Conclusions The CCMs showed successful Pt recovery (approximately 100% within experimental error) when carrying out the oxidative leach with selectivity for Pt. Following this, the reductive leach showed good recovery of Ir, with a stronger recovery in the repeat experiment (> 95%). Overall, >97% of the PGMs were recovered from the CCM material. Ionomer Recovery 6.0 g of anhydrous LiOH and 250 g of water were weighed and the LiOH dissolved in the water. 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. Figure 3 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. Figure 4 shows an example of process steps (pre-autoclave). The membrane was brown in colouration as indicated in the figure. After being refluxed in the solution of lithium hydroxide 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. In the final step of the pre-autoclave process shown in Figure 4, the solid polymer salt membrane material was washed in water to remove any residual LiOH solution. Figure 5 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 6 shows a further step of autoclaving the membrane following the treatment process as shown in Figure 4 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. Figure 7 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. Ionomer recovery from PGM leached CCM Saltation Pt-leached CCM (approx. 650 g, approx. 0.61 mol SO3) was placed into a 5 L beaker. Anhydrous LiOH (36.519 g, 1.52 mol, 2.5 mol equivalent) was added to DI water (3 L) and stirred until dissolved. The LiOH solution was then added to the Pt-leached CCM and stirred using an overhead stirrer for 1.5 hours. The liquid was then decanted off. DI water (2.5 L) was then added to the CCM and stirred for 1.5 hours, decanted, and repeated with fresh DI water a further two times. Dispersion A sample of CCM (107.6 g wet, 67.6 g dry, approx. 50 g ionomer, 62.5 mmol SO3) was added to DI water (410 mL) and subjected to a hydrothermal process under nitrogen at 240°C and 40 bar (4000 kPa) pressure, similar to the process shown in Figure 6 to disperse the ionomer. Once cooled the pH of the resulting dispersion was measured at pH 7. The ionomer dispersion was passed through a Buchner funnel (without filter paper) to remove ePFTE and carbon. The filtrate was subjected to centrifugation at 15000 rpm for 15 minutes to remove carbon, affording a clear dispersion. Figure 8 shows a 19F NMR for the dispersed ionomer without any significant degradation products [19F NMR (376 MHz, D2O) 5 -80 (b, OCF2, CF3), -118 (b, CF2S), -122 (b, (CF2)n), -138 (b, CF), -144 (b, CFCF3)]. Ionomer recovery from CCM containing Pt Saltation Ionomer recovery in the presence of PGM catalyst material has shown to cause degradation of the ionomer material. NaOH (1.2 g, 0.03 mol) was dissolved in DI water (500 mL) followed by addition of CCM pieces which contain Pt (18.16 g, approx. 11.97 g ionomer, 0.015 mol SO3 ). The NaOH / CCM mixture was rolled at 60 rpm for 18 hours to salt the sulphonic acid groups. Dispersion The salted CCM suspension was then subject to a hydrothermal process under nitrogen at 240°C and 40 bar (4000 kPa) pressure. Once cooled the pH of the resulting dispersion was measured at pH 8. The ionomer dispersion was passed through a Buchner funnel (without filter paper) to remove ePFTE and PGM catalyst material. The filtrate was subjected to centrifugation at 15000 rpm for 15 minutes to remove carbon, affording a clear dispersion. Figure 9 shows the presence of PFAS degradation products as sharp peaks in the 19F NMR of the ionomer dispersion [19F NMR (376 MHz, D2O) 8 -80 (b, OCF2), -115 (b, CF2S), -117 (t, J = 8 Hz, HCF2CF2CF2SO3H), -119 (s, NaF), -123 (b, (CF2)n), -125 (b, CF2), -130 (m, HCF2CF2CF2SO3H), -137 (dp, J = 50 Hz, J = 8 Hz, HCF2CF2CF2SO3H), 137 (b, CF)]. An ion-selective electrode (ISE) was used to analyse free fluoride in the resulting ionomer dispersion, showing >400 ppm of fluoride. Gel permeation chromatography (GPC) showed a decrease in average molecular weight (Mw) from 799,703 Da to 375,803 Da. The equivalent weigh (EW) of the recovered ionomer had also increased from 750 to 843, evidence of side-chain cleavage. Ionomer recovery from ionomer membrane with recombination layer Saltation NaOH (3.02 g, 0.08 mol) was dissolved in DI water (500 mL) followed by addition of membrane pieces which contained a Pt recombination layer (31.28 g). The NaOH / CCM mixture was rolled at 60 rpm for 18 hours to salt the sulphonic acid groups. Membrane pieces were then filtered and washed with DI water until washings were pH 7. Dispersion A sample of washed membrane pieces (5.14 g wet, 4.82 g dry) was then subject to a hydrothermal process under nitrogen at 240°C and 40 bar (4000 kPa) pressure. Once cooled the pH of the resulting dispersion was measured at pH 7. The ionomer dispersion was passed through a Buchner funnel with 0.22 pm filter paper to remove ePTFE and PGM catalyst material. Figure 10 shows the presence of PFAS degradation products as sharp peaks in the 19F NMR of the ionomer dispersion [19F NMR (376 MHz, D2O) 8 -81 (b, OCF2, CF3), -84 (s, CF3CF2SO3H), -118 (s, CF3CF2SO3H), -119 (b, CF2S), -119 (s, NaF), -123 (b, (CF2)n), -139 (b, CF), -146 (b, CFCF3)]. An ISE was used to analyse free fluoride in the resulting ionomer dispersion, showing >20 ppm of fluoride. As with the previous example, this illustrates that ionomer recovery in the presence of PGM catalyst material causes degradation of the ionomer material. As such, the preferred approach is to leach the PGM material from the ionomer material prior to ionomer dispersion. Summary Catalyst coated membranes from water electrolyser products contain Pt and Ir. This specification demonstrates recovery of both metals and their recycling into useable products, optionally back into the catalysts themselves or their precursors. An oxidative leach of the CCMs in HCI with an oxidant such as chlorine, hydrogen peroxide or sodium chlorate can recover ~99% Pt from the material. The platinum can be concentrated up to generate a sample of chloroplatinic acid (CPA) which meets 30 wt% Pt specifications. This can be used in the manufacture of Pt / C catalyst with carbon being taken from supply or potentially recycled sources. If additional clean up steps are required, the material can be worked up to sponge, which can then be converted to CPA of the required specification as before and then made into Pt / C catalyst powder, which will eventually go back into a CCM. Alternatively, techniques such as chromatography or other solid phase extraction can be used to purify the solution before conversion to CPA or sponge. The CCMs from water electrolysers can then be reductively leached to recover the iridium from iridium oxide. The membrane, once shredded, is suspended in water / hydrazine and stirred to allow reduction of the iridium of the water electrolyser iridium oxide catalyst. This is then treated with HCI to enable an Ir chloride solution to form, heating the solution to enable better reaction kinetics. The resulting Ir chloride liquor can then be treated to make Ir based products. For example, removal of impurities and worked up to Ir sponge which can be used to make a variety of products or the material can be reworked into an IrOx catalyst. This catalyst can be used in an ink and recycled back into a CCM. Due to the presence of Pt in these materials, an oxidative Pt leach is to be carried out first in order to minimise mixing Ir and Pt chlorides. Due to the slow oxidation of Pt / C present in the CCM, approximatively 20-40% of the Pt is leached via the reductive conditions if not removed prior to the reductive leach. Therefore, an oxidative leach using HCI and an oxidant should be carried out prior to the reductive process. The remaining residues contain ionomer, PTFE support, and carbon. Ionomer can be recovered by solvent dispersal. Advantageously, the ionomer is converted to salt form first by treatment with a base prior to solvent dispersal and re-protonation via ion exchange for re-use in new CCMs. By removal of the PGMs prior to ionomer dispersal, PGM driven damage of the ionomer during the dispersal process is avoided. 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

1. A method of recycling a waste catalyst coated membrane material comprising an ionomer membrane, at least one catalyst comprising platinum, palladium and / or ruthenium, and at least one catalyst comprising iridium, the method comprising:(a) treating the waste catalyst coated membrane material with a heated solution comprising an acid and an oxidant, wherein the 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) after step (a), leaching iridium from the waste catalyst coated membrane material using a heated solution comprising an acid and a reducing agent and separating the solution comprising the leached iridium from remaining solid componentsof the waste catalyst coated membrane material; and(c) after steps (a) and (b), treating the waste catalyst coated membrane material with a heated solvent to disperse the ionomer membrane and recover a dispersion of ionomer.

2. A method according to claim 1, wherein the acid used in one or both of the iridium leach and the platinum, palladium and / or ruthenium leach is hydrochloric acid.

3. A method according to claim 1 or 2,wherein one or both of the solution used for the leach of platinum, palladium and / or ruthenium and the solution used for the leach of iridium are heated to a temperature of: at least 50°C, 60°C, or 70°C; no more than 160°C, 120°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.

4. A method according to any preceding claim,wherein, in step (a), the oxidant comprises a halide salt, a chlorate salt, chlorine gas, or hydrogen peroxide.

5. A method according to any preceding claim,wherein, in step (a), the solution for leaching the 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 one or both of the solution used for the leach of the platinum, palladium and / or ruthenium and the solution used for the leach of iridium has an acid concentration of: no less than 4 M, 5 M, 5.5 M, or 6 M; no more than 15 M, 12 M, 10 M, or 7 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 (b), the reducing agent is hydrazine.

8. A method according to any preceding claim,wherein, in step (b), the solution for leaching iridium has a reducing agent concentration of: at least 1 wt%, 3 wt%, or 5 wt%; no more than 35wt%, 30 wt%, 20 wt%, 10 wt%, or 7.5 wt%; or within a range defined by any combination of the aforementioned lower and upper limits9. A method according to any preceding claim,wherein, in step (b), the reducing agent is added to the waste catalyst coated membrane material first and then followed by addition of the acid.

10. A method according to any preceding claim,wherein after separating the solution containing the leached platinum from remaining solid components of the waste catalyst coated membrane material, the solution is concentrated to yield chloroplatinic acid comprising at least 30 wt% Pt.

11. A method according to any preceding claim,wherein, in step (c), 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.

12. A method according to any preceding claim,wherein, in step (c), 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.

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

14. A method according to claim 13,wherein the ionomer dispersion is subjected to an ion exchange process to re-protonate the ionomer in the dispersion.

15. A method according to any preceding claim, wherein the catalyst comprising iridium is an iridium oxide.

16. A method according to any preceding claim, wherein the catalyst comprising platinum is a platinum-on-carbon catalyst.15