Recycling of catalyst coated membrane components

Abstract

A method of recovering material from a catalyst coated membrane which comprises an ionomer, a platinum group metal, and one or more of a metal catalyst, a carbon catalyst support, and a membrane reinforcement, the method comprising: (a) treating the material with a solvent to form an ionomer dispersion; (b) subjecting the ionomer dispersion to forced filtration in order to produce a filter cake comprising one or more of the metal catalyst, the carbon catalyst support and the membrane reinforcement, and a filtrate of the ionomer dispersion; and (c) acid leaching to extract the platinum group metal, wherein the acid leaching is either: (i) applied to the waste ionomer material prior to forming the ionomer dispersion; or (ii) applied to the filter cake material after filtering. The membrane can be from a fuel cell or hydrogen producing water electrolysers.

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 specification is concerned with providing a method of recycling a waste ionomer material which is capable of separating and recovering both platinum group metal and ionomer components in purified form with high yields, whilst also ensuring that other component materials within the waste ionomer material, such as metal catalyst material, carbon catalyst support material and / or membrane reinforcement material, are separated and recovered during processing. The present specification provides a method of recycling a waste ionomer material comprising at least one ionomer, at least one platinum group metal, and one or more of a metal catalyst material (e.g., including the platinum group metal), a carbon catalyst support material, and a membrane reinforcement material, the method comprising: (a) treating the waste ionomer material with a solvent to disperse the ionomer and form an ionomer dispersion which includes one or more of the metal catalyst material, the carbon catalyst support material, and the membrane reinforcement material; (b) subjecting the ionomer dispersion to a forced filtration technique in which a force is actively applied to the ionomer dispersion in order to force the ionomer dispersion through a filter to produce a filter cake on the filter comprising one or more of the metal catalyst material, the carbon catalyst support material, and the membrane reinforcement material, and a filtrate of the ionomer dispersion; and (c) using one or more acid leaches to extract the platinum group metal, wherein either: (i) the one or more acid leaches are applied to the waste ionomer material to extract the platinum group metal from the waste ionomer material prior to forming the ionomer dispersion in step (a); or (ii) the one or more acid leaches are applied to the filter cake material after step (b) to extract the platinum group metal from the filter cake material. The forced filtration technique can be selected from one of: centrifugal filtration; negative pressure (i.e., vacuum) filtration; and positive pressure filtration. Centrifugal filtration has been found to be particularly effective at separating ionomer from carbon catalyst support material and membrane reinforcement material to produce a high purity ionomer dispersion with high yields. It may be noted that while filtration has previously been used, it has found that a forced filtration technique such as centrifugal filtration has been found to be significantly more effective at producing a high purity ionomer dispersion with high yields. It may also be noted that centrifugal processing of ionomer material has also previously been disclosed, but not in combination with filtration to provide a centrifugal filtration process. For example, US7255798 uses centrifugation to separate ionomer from a platinum-on-carbon catalyst material but does not consider use of centrifugal filtration to collect solids such as carbon catalyst support material and membrane reinforcement material. WO2016156815 also mentions centrifugation but does not disclose centrifugal filtration to separate ionomer dispersion and collect solids such as carbon catalyst support material and membrane reinforcement material. The waste ionomer material may additionally comprise one or both of a seal material and a gas diffusion layer material in which case the filter cake formed in step (b) comprises one or both of the seal material and the gas diffusion layer material. After separating the ionomer dispersion via the forced filtration technique, the filter cake material is processed to separate and recover one or more of the metal catalyst material, the carbon catalyst support material, the membrane reinforcement material, the seal material and the gas diffusion layer material. For example, the filter cake material can be processed to separate and recover one or more of the metal catalyst material, the carbon catalyst support material, the membrane reinforcement material, the seal material and the gas diffusion layer material by forming a slurry of the filter cake material and performing one or more filtrations, optionally forced filtrations, of the slurry to achieve separation based on different particle sizes of the materials. Typically, the carbon catalyst support material and / or the metal catalyst material has a smaller particle size than the membrane reinforcement material, and a suitable filter is selected such that the filtration of the slurry results in a filtrate comprising the carbon support material and / or the metal catalyst material with the membrane reinforcement material capture on the filter. According to certain preferred methods, the one or more acid leaches are applied to the waste ionomer material to extract the platinum group metal from the waste ionomer material prior to forming the ionomer dispersion and processing the ionomer dispersion via the forced filtration process. In this case, it has been found that the platinum group metal can be acid leached while retaining the carbon catalyst support material and the membrane reinforcement material in solid form with sufficient particle size that after subsequently dispersing the ionomer, the carbon catalyst support material and the membrane reinforcement material can be efficiently separated via forced filtration. In the alternative methodology, the ionomer dispersion and forced filtration is performed prior to the acid leaching to extract platinum group metal material. In that case, during forced filtration, the carbon catalyst support material and / or metal catalyst material which is filtered comprises the platinum group metal catalyst material. The acid leaching is then applied to the filter cake material to extract the platinum group metal from the filter cake material. The acid leach may be applied to the filter cake material which still comprises a mixture of the carbon catalyst support material, the membrane reinforcement material, and optionally the seal material and / or the gas diffusion layer material. Alternatively, the filter cake material can be first processed to separate the platinum group metal catalyst material, optionally including the carbon catalyst support material, and only that portion of the filter cake material is then subjected to acid leaching. That is, according to different versions of the present methodology the acid leaching may be applied to filter cake material before or after the filter cake material is processed to separate and recover one or more of the metal catalyst material, the carbon catalyst support material, the membrane reinforcement material, the seal material and the gas diffusion layer material. For waste ionomer materials which include platinum, palladium, and / or ruthenium, the acid leaching may include an acid leach which uses a heated solution comprising an acid and an oxidant, wherein the platinum, palladium, and / or ruthenium is leached into the solution. For waste ionomer materials which include iridium, the acid leaching may include an acid leach which uses a heated solution comprising an acid and a reducing agent, wherein iridium is leached into the solution. For waste ionomer materials which include both platinum, palladium, and / or ruthenium and also iridium, the acid leaching may include both the aforementioned oxidative and reductive leaches. While these two leaches can be performed in either order, it has been found that the oxidative leach is selective for platinum, palladium, and / or ruthenium with substantially no iridium being leached. In contract, the reductive iridium leach also leaches a proportion of platinum, palladium, and / or ruthenium. While a mixed iridium and platinum, palladium, and / or ruthenium solution can be further processed to separate the PGMs, it is advantageous to perform the oxidative leach first followed by the reductive leach so that the platinum, palladium, and / or ruthenium can be separate from the iridium upfront in the process. This improves the efficiency of the process and reduces downstream separation requirements. In light of the above, it is preferred that the oxidative acid leach is performed prior to the reductive acid leach. The methodology also includes treating the waste ionomer material with a heated solvent to disperse the ionomer and it is preferred that this is performed after the oxidative and reductive leaches. This is because it has been found that if the ionomer dispersion step is performed with PGM catalyst material still present, the PGM catalyst can drive degradation of the ionomer during dispersion. As such, it is preferred that the PGM material is removed prior to the ionomer dispersion step. 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. Furthermore, 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. Further still, it is preferred that the ionomer is treated with a base to convert the ionomer to salt form prior to dispersing the ionomer in the solvent. It has been found that these conditions achieve a highly dispersed ionomer while retaining the carbon catalyst support material and the membrane reinforcement material in solid form with sufficient particle size that the carbon catalyst support material and the membrane reinforcement material can be efficiently separated from the highly dispersed ionomer via forced filtration. Subsequently, after the forced filtration, the ionomer dispersion can be subjected to an ion exchange process to reprotonate the ionomer. 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 according to the present specification; Figure 2 illustrates a waste CCM recycling process comprising a platinum leach followed by an iridium leach followed by ionomer dispersion; Figure 3 shows a more detailed example illustrating 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; (v) separating the ionomer dispersion from other components including carbon catalyst support material and / or membrane reinforcement material via a forced filtration technique; and (vi) subjecting the ionomer dispersion to an ion exchange process to re-protonate the ionomer material; Figure 4 shows FTIR data for fluorinated polymer membrane material (301), fluorinated polymer salt material formed after treatment in water and base (303), and fluorinated polymer salt material formed after treatment in water and base followed by a water wash (304); Figure 5 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 6 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 7 shows a further step of autoclaving the membrane following the treatment process as shown in Figure 3 to disperse the membrane in water; and Figure 8 shows a further step (post-autoclave) of ion exchange to convert the dispersed polymer salt back to protonated acid form. Detailed Description As described in the summary section and illustrated in Figure 1, the present specification provides a method of recycling a waste ionomer material comprising at least one ionomer, at least one platinum group metal, and one or moreof a metal catalyst material (e.g., including the platinum group metal), a carbon catalyst support material and / or a membrane reinforcement material, the method comprising: (a) treating the waste ionomer material with a solvent to disperse the ionomer and form an ionomer dispersion which includes one or more of the metal catalyst material, the carbon catalyst support material, and / or the membrane reinforcement material; (b) subjecting the ionomer dispersion to a forced filtration technique in which a force is actively applied to the ionomer dispersion in order to force the ionomer dispersion through a filter to produce a filter cake on the filter comprising one or more of the metal catalyst material, the carbon catalyst support material, and / or the membrane reinforcement material, and a filtrate of the ionomer dispersion; and (c) using one or more acid leaches to extract the platinum group metal, wherein either: (i) the one or more acid leaches are applied to the waste ionomer material to extract the platinum group metal from the waste ionomer material prior to forming the ionomer dispersion in step (a); or (ii) the one or more acid leaches are applied to the filter cake material after step (b) to extract the platinum group metal from the filter cake material. The forced filtration technique can be selected from one of: centrifugal filtration; negative pressure (i.e., vacuum) filtration; and positive pressure filtration. Centrifugal filtration has been found to be particularly effective at separating ionomer from carbon catalyst support material and membrane reinforcement material to produce a high purity ionomer dispersion with high yields. The waste ionomer material may additionally comprise one or both of a seal material and a gas diffusion layer material in which case the filter cake formed in step (b) comprises one or both of the seal material and the gas diffusion layer material. After separating the ionomer dispersion via the forced filtration technique, the filter cake material is processed to separate and recover one or more of the carbon catalyst support material, the membrane reinforcement material, the seal material and the gas diffusion layer material. For example, the filter cake material can be processed to separate and recover one or more of the carbon catalyst support material, the membrane reinforcement material, the seal material and the gas diffusion layer material by forming a slurry of the filter cake material and performing one or more filtrations, optionally forced filtrations, of the slurry to achieve separation based on different particle sizes of the materials. Typically, the carbon catalyst support material has a smaller particle size than the membrane reinforcement material, and a suitable filter is selected such that the filtration of the slurry results in a filtrate comprising the carbon support material with the membrane reinforcement material capture on the filter. According to certain preferred methods, the one or more acid leaches are applied to the waste ionomer material to extract the platinum group metal from the waste ionomer material prior to forming the ionomer dispersion and processing the ionomer dispersion via the forced filtration process. In this case, it has been found that the platinum group metal can be acid leached while retaining the carbon catalyst support material and the membrane reinforcement material in solid form with sufficient particle size that after subsequently dispersing the ionomer, the carbon catalyst support material and the membrane reinforcement material can be efficiently separated via forced filtration. In the alternative methodology, the ionomer dispersion and forced filtration is performed prior to the acid leaching to extract platinum group metal material. In that case, the acid leaching is applied to the filter cake material to extract the platinum group metal from the filter cake material. While the leaching and dispersal steps may be performed in any order, one preferred methodology is shown in Figure 2 which illustrates a waste CCM recycling process comprising a platinum leach followed by an iridium leach followed by ionomer dispersion. In this example, a method of recycling a waste catalyst coated membrane material comprising an ionomer membrane, at least one catalyst comprising platinum (e.g., a platinum-on-carbon catalyst), palladium and / or ruthenium and at least one catalyst comprising iridium (e.g., an iridium oxide catalyst) is provided. The method comprises: (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) 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, palladium, and / or ruthenium, the iridium, and the ionomer materials without significant degrading the ionomer and ensuring 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 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. 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 (and / or palladium and / or ruthenium) 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 3 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; (v) separating, via forced filtration, the ionomer dispersion from other components (carbon and / or membrane reinforcement material); and (vi) 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 Anhydrous LiOH (6.0 g) was added to water (250 g) and the LiOH dissolved in the water. Membrane pieces were submerged in the LiOH solution and heated to reflux (1 hour). The resultant mixture was washed out with water (4 X 100 mL). The remaining water was decanted to leave (wet) membrane pieces. Water (250 g) was added to the (wet) membrane pieces, and heated to reflux (1 hour). The water was then decanted and the solid product dried in vacuo. Figure 4 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 5 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 6 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 7 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) autogenous pressure. This resulted in a (non-basic) aqueous dispersion of the polymer salt. The aqueous dispersion of the polymer (ionomer) salt is then subjected to a centrifugal filtration to separate the ionomer dispersion from solid carbon catalyst support and solid polytetrafluoroethylene membrane reinforcement material. For example, a recycled dispersion containing ionomer, solid carbon catalyst support and solid polytetrafluoroethylene was added to centrifuge tubes containing a 0.45 pm PVDF filter. The tubes were subjected to centrifugation for 2 x 6 minutes at approximately 3000 g relative centrifugal force to produce a solid cake on the filter consisting of black (carbon) and white (PTFE) solids and a dispersion containing ionomer at the bottom of the tube. Figure 8 shows a further subsequent step 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. Summary The present specification provides a method of recycling a waste ionomer material which is capable of separating and recovering both platinum group metal and ionomer components in purified form with high yields, whilst also ensuring that other component materials within the waste ionomer material, such as carbon catalyst support material and membrane reinforcement material, are separated and recovered during processing. 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 ionomer material comprising at least one ionomer, at least one platinum group metal, and one or more of a metal catalyst material, a carbon catalyst support material, and a membrane reinforcement material, the method comprising:(a) treating the waste ionomer material with a solvent to disperse the ionomer and form an ionomer dispersion which includes one or more of the metal catalyst material, the carbon catalyst support material, and the membrane reinforcement material;(b) subjecting the ionomer dispersion to a forced filtration technique in which a force is actively applied to the ionomer dispersion in order to force the ionomer dispersion through a filter to produce a filter cake on the filter comprising one or more of the metal catalyst material, the carbon catalyst support material, and the membrane reinforcement material, and a filtrate of the ionomer dispersion; and(c) using one or more acid leaches to extract the platinum group metal, wherein either: (i) the one or more acid leaches are applied to the waste ionomer material to extract the platinum group metal from the waste ionomer material prior to forming the ionomer dispersion in step (a); or (ii) the one or more acid leaches are applied to the filter cake material after step (b) to extract the platinum group metal from the filter cake material.

2. A method according to claim 1,wherein the forced filtration technique is selected from one of: centrifugal filtration; negative pressure filtration; positive pressure filtration; cross-flow filtration; dead-end filtration; and vacuum filtration.

3. A method according to any preceding claim,wherein the waste ionomer material additionally comprises one or both of a seal material and a gas diffusion layer material and the filter cake formed in step (b) comprises one or both of the seal material and the gas diffusion layer material.

4. A method according to any preceding claim,wherein after separating the ionomer dispersion via the forced filtration technique, the filter cake material is processed to separate and recover one or more of the metal catalyst material, the carbon catalyst support material, the membrane reinforcement material, the seal material and the gas diffusion layer material.

5. A method according to claim 4,wherein the filter cake material is processed to separate and recover one or more of the metal catalyst material, the carbon catalyst support material, the membrane reinforcement material, theseal material and the gas diffusion layer material by forming a slurry of the filter cake material and performing one or more filtrations of the slurry to achieve separation based on different particle sizes of the materials.

6. A method according to claim 5,wherein the carbon catalyst support material and / or the metal catalyst material has a smaller particle size than the membrane reinforcement material, and a suitable filter is selected such that the filtration of the slurry results in a filtrate comprising the carbon support material and / or the metal catalyst material with the membrane reinforcement material capture on the filter.

7. A method according to claim 4, 5, or 6,wherein, step c(ii) is used in claim 1, such that the one or more acid leaches are applied to the filter cake material to extract the platinum group metal from the filter cake material, and the one or more acid leaches are applied before or after the filter cake material is processed to separate and recover one or more of the metal catalyst material, the carbon catalyst support material, the membrane reinforcement material, the seal material and the gas diffusion layer material.

8. A method according to any preceding claim,wherein step (c) includes an acid leach which uses a heated solution comprising an acid and an oxidant, wherein platinum, palladium, and / or ruthenium is leached into the solution.

9. A method according to any preceding claim,wherein step (c) includes an acid leach which uses a heated solution comprising an acid and a reducing agent, wherein iridium is leached into the solution.

10. A method according to any preceding claim,wherein step (a) includes treating the waste ionomer material with a heated solvent to disperse the ionomer.

11. A method according to claims 8 to 10,wherein the oxidative acid leach of claim 12 is performed prior to the reductive acid leach of claim 13.

12. A method according to claim 10 or 11,wherein 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.

13. A method according to any one of claims 10 to 12,wherein 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.

14. A method according to any one of claims 10 to 13,wherein the ionomer is treated with a base to convert the ionomer to salt form prior to dispersing the ionomer in the solvent.

15. A method according to claim 14,wherein the ionomer dispersion is subjected to an ion exchange process to re-protonate the ionomer after the forced filtration of the ionomer dispersion to separate the ionomer from the other materials.15

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