Recycling of catalyst coated membrane components

Abstract

A method of recycling a waste catalyst coated membrane material comprising an ionomer and at least one catalyst comprising platinum, palladium and / or ruthenium on a carbon support material comprises t

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 being 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 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 or PtNi-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 particularly concerned with the recycling of waste catalyst coated membrane materials which comprise ionomer and at least one catalyst comprising platinum, palladium and / or ruthenium on a carbon support material. The present specification provides a method of recycling a waste catalyst coated membrane material comprising an ionomer and at least one catalyst comprising platinum, palladium and / or ruthenium on a carbon support material, 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 with the carbon support material remaining in solid form, the solution then being 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 separate and recover the ionomer dispersion from the solid carbon support material, wherein the dispersion of ionomer is performed before or after the leaching of the platinum, palladium and / or ruthenium in step (a); (c) processing the solution comprising leached platinum, palladium and / or ruthenium to separate base metal and recover the platinum, palladium and / or ruthenium; and (d) after steps (a) and (b) in which both the ionomer and the platinum, palladium and / or ruthenium are separated from the carbon support material, the remaining solid carbon support material is recovered for re-use. It has been found that an oxidative acid leach can be used to separate and recover the platinum, palladium and / or ruthenium from a catalyst comprising platinum, palladium and / or ruthenium on a carbon support material. Furthermore, the carbon support material subjected to such a leaching process can be recovered and re-used. For example, the recovered carbon support material can be re-used in manufacturing new catalyst material, optionally including blending with fresh carbon support material. Alternatively, the recovered carbon support material can be re-used in another application, e.g., as an activated carbon material such as in a filtration application. Further still, ionomer material subjected to such a leaching process can also be recovered and re-used to manufacture new ionomer membranes and catalyst coated membranes. The catalyst material can be platinum-on-carbon, platinum-cobalt-on-carbon, or platinum-nickel-on-carbon. For those catalyst materials which comprise a base metal, such as cobalt or nickel, the base metal is also leached by the oxidative acid leach. This is also true for waste platinum-on-carbon catalyst materials which have become contaminated with base metal during use or during processing of the waste material. As such, after leaching, the method comprises processing the solution to separate base metal contamination and recover the platinum, palladium and / or ruthenium. For example, the solution can be processed by addition of a base to precipitate the base metal material, which can be recovered and re-used, and then the solution can be re-acidified and processed to produce the desired PGM product species, e.g., chloroplatinic acid or a PGM sponge. Alternative technologies to remove base metals and impurities include solid phase extraction or chromatography. The present methodology can thus recycle waste catalyst coated membrane materials to recover PGMs, ionomer, base metals, and carbon support material for re-use. Further details of the methodology are provided in the detailed description below. 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 drawing, in which: Figure 1 shows a waste CCM recycling process according to the present specification; 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; 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; 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; 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; Figure 6 shows a further step (post-autoclave) of ion exchange to convert the dispersed polymer salt back to protonated acid form; Figure 7 shows XPS spectra for carbon support material which is leached compared to starting material; and Figures 8(a) and 8(b) show Raman analysis for carbon support material which is leached compared to starting material. 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 and at least one catalyst comprising platinum, palladium and / or ruthenium on a carbon support material, 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 with the carbon support material remaining in solid form, the solution then being 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 separate and recover the ionomer dispersion from the solid carbon support material, wherein the dispersion of ionomer is performed before or after the leaching of the platinum, palladium and / or ruthenium in step (a); (c) processing the solution comprising leached platinum, palladium and / or ruthenium to separate base metal and recover the platinum, palladium and / or ruthenium; and (d) after steps (a) and (b) in which both the ionomer and the platinum, palladium and / or ruthenium are separated from the carbon support material, the remaining solid carbon support material is recovered for re-use. The waste catalyst coated membrane material to be recycled can be a catalyst coated membrane or one or more ionomer containing catalyst materials, e.g., ionomer containing catalyst layers which have been separated from an ionomer membrane or waste catalyst ink materials comprising ionomer. The catalyst material may be coated on an ionomer membrane and / or disposed within an ionomer membrane (either as a layer within the ionomer membrane or dispersed through a thickness of the ionomer membrane. The carbon support material can be in the form of a particulate carbon powder and the platinum, palladium and / or ruthenium is disposed on the particles of carbon powder. Examples include platinum-on-carbon, platinum-cobalt-on-carbon, and platinum-nickel-on-carbon. In step (a), the acid used in the leach of platinum, palladium and / or ruthenium can be hydrochloric acid and the oxidant can be a chlorate salt, chlorine gas, or hydrogen peroxide. The leaching solution may have an acid concentration of: no less than 4 M, 5 M, or 5.5 M; no more than 12 M, 10 M, 7 M, 6.5 M, or 6 M; or within a range defined by any combination of the aforementioned lower and upper limits. Furthermore, the leaching solution 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., in a range 0.01 to 0.10 mol / l. For the leaching step, the 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. In step (b), 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. 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. In step (c), after leaching the platinum, palladium and / or ruthenium and separating the solution from remaining solid components of the waste catalyst coated membrane material, the solution can be treated with a base to increase the pH of the solution (e.g., to between 7.5 and 10, optionally between 8 and 10) such that the base metal, optionally including cobalt and / or nickel, in the solution is precipitated and separated from the solution, optionally via filtration. The base may comprise one or both of NaHCOs and NaOH. After precipitating and separating the base metal, the solution can be reacidified and the platinum, palladium and / or ruthenium is recovered as a salt or PGM sponge. Alternative technologies to remove base metals and impurities include solid phase extraction or chromatography. In addition to recovery of ionomer, PGMs, and base metal components, the methodology is also capable of recovering the catalyst carbon support material. After steps (a) and (b) in which both the ionomer and the platinum, palladium and / or ruthenium are separated from the carbon support material, the remaining solid carbon support material can be washed, dried, and re-used as a carbon support material in the manufacture of new catalyst material comprising platinum, palladium and / or ruthenium on the carbon support material. Optionally, the recovered carbon support material is blended with fresh carbon support material when re-used to manufacture the new catalyst material. If the waste catalyst coated membrane material also contains an iridium catalyst, such as an iridium oxide catalyst material, then the iridium can also be recovered by, for example, a reductive acid leaching process. If a leach is used then this differs from that used for leaching of platinum, palladium and / or ruthenium. In particular, a reducing agent (e.g., selected from one of hydrazine, NaBH4, and ammonium oxalate) rather than an oxidizing agent is used for the iridium leach. Furthermore, the acid solution, e.g., a HCI solution, may also be more concentrated for the iridium leach when compared to the leach for platinum, palladium and / or ruthenium. For example, the acid used for the iridium leach may be: no less than 6M, 7M, or 8M; no more than 15M, 12M, or 10M; or within a range defined by any combination of the aforementioned lower and upper limits (e.g. in a range 8 M to 12 M). As an alternative to recovering the iridium via a reductive acid leach, the iridium catalyst material may be directly recovered as a solid material. In that case, the solid iridium catalyst material should be separated from solid carbon material, e.g., by creating a slurry of the remaining solid components after removal of ionomer and platinum, palladium and / or ruthenium, and separating the different solid components remaining via differential particle size. The present methodology as described above can thus recycle waste catalyst coated membrane materials to recover PGMs, ionomer, base metals, and carbon support material for re-use. Examples Platinum Recovery Oxidative leach of various Pt and Ir containing catalyst powders using NaCIOi The aim of these experiments was to determine if PGM can be recovered from various different catalyst materials using an oxidative leach. NaClOa was used as the oxidant in excess with HCI as the acid dissolution and chloride source. The catalysts leached in this set of experiments included: • Pt / C • PtNi / C • PtRu / C • PtCo / C • IrOx • IrRuOx • IrTaOx • Ir black Method of Leaching 1. 200 rnL of 6 M HCI was added to a 3 neck, 500 mL round bottom flask with a condenser and temperature probe attached and magnetic stirrer bar. 2. The desired amount of NaCIOs was then added to the vessel slowly with stirring at 500 rpm to preoxidise the solution (1:2 molar ratio of metakNaCIOs). 3. The catalyst powder was then added to the vessel slowly. 4. The solution was heated to 70°C with stirring at 500 rpm. 5. Once solution reached temperature, it was left to heat at 70°C for 50 mins. 6. Solution was left to cool. 7. Once cooled, solution was filtered using 0.45 pm cellulose nitrate filter paper and a Buchner funnel. 8. The liquor and washings were collected in separated bottles and the mass of filter paper recorded. Results Catalyst PGM Metal Other Metal Yield % Yield % Pt / C 85 - PtNi / C 80 25 (Ni) PtRu / C 3.0 2.0 (Ru) PtCo / C 79 31 (Co) IrOx 0.46 - IrTaOx 0 0(Ta) IrRuOx 0 0 (Ru) Ir black 0.90 Discussion and Conclusions The percentage yield of Pt is approximately similar for Pt / C, PtNi / C and PtCo / C at ~80% Pt. However, the PtRu / C gave a significantly lower % Pt yield compared to the other catalysts. The base metal yield is lower than the Pt yield for the same catalyst. The percentage yield of Ir obtained in these oxidative leaches is zero or almost zero for all Ir containing catalysts suggesting the oxidative leach using NaCIOs is not successful at leaching Ir. The aim of these experiments was to understand what conditions could successfully leach PGMs. The results have shown that Pt can be leached from several catalysts when using NaCIOs as the oxidant. However, these oxidative leach conditions are not suitable to leach Ir. Oxidative leach of Pt and Ir containing catalysts using H2O2 as the oxidant The aim of these experiments was to determine if PGM can be recovered from various different catalyst materials using an oxidative leach. H2O2 was used as the oxidant in excess with HCI as the acid dissolution and chloride source. The catalysts leached in this set of experiments included: • Pt / C • PtNi / C • IrOx • PtCo / C • PtRu • IrRuOx • Ir black • IrTaOx Method of Leaching 1. 200 mL of 12 M HCI was added to a 3 neck, 500 mL round bottom flask with a condenser and temperature probe attached and magnetic stirrer bar. 2. The desired amount of H2O2 was then added to the vessel slowly with stirring to pre-oxidise the solution (1:2 molar ratio of metal:H2O2). 3. The catalyst powder was then added to the vessel slowly. 4. The solution was heated to 70°C with stirring at 500 rpm. 5. Once the solution reached temperature, it was left to heat at 70°C for 50 mins. 6. Solution was left to cool. 7. Once cooled, solution was filtered using a 0.45 pm cellulose nitrate filter paper and Buchner funnel. 8. The liquor and washings were collected in separated bottles and the mass of filter paper recorded. Results Catalyst PGM Metal Yield % Other Metal Yield % Pt / C 90 - PtNi / C 87 40 (Ni) PtRu / C 40 34 (Ru) PtCo / C 92 31 (Co) IrOx 0.7 - IrTaOx 0 0(Ta) IrRuOx 0 0 (Ru) Ir black 1.7 Discussion and Conclusions Oxidative leaching of the Pt catalysts demonstrated approximately a 90% Pt yield from Pt / C, PtNi / C and PtCo / C catalyst powders. Pt yield was significantly lower for PtRu / C. The alloying metals were also leached under these conditions. No Ir uptake was observed for IrTaOx or IrRuOx and only a small percentage of Ir was recovered for IrOx and Ir black suggesting HCI / H2O2 oxidative leaching conditions cannot recover Ir effectively. The aim of this experiment was to understand if HCI / H2O2 could effectively leach PGMs from catalyst powders. Results have shown this to be the case for Pt containing catalysts, but not for Ir based catalysts. CCM HCI / Chlorate Leach Trial This trial leaches the Pt from catalyst coated membranes (CCMs) which have failed the QC process in the manufacturing factory. For this method, the CCM polymer seal has already been removed before cutting into pieces 2x3 cm2 in size. Once prepared, HCI / chlorate was used to leach the Pt from the CCM. Leaching Method A 500 ml flange vessel was set up with an overhead stirrer with a PTFE stirrer and stirrer guide on top of the hot plate. A temperature probe, connected to the hot plate, and condenser with cooling water were also fitted. The initial mass of CCM was 11.81 g. The vessel was charged with the CCM pieces (approximately 2 x 3 cm2) and 400 ml 6M HCI. The reaction mixture was set to stir at 250 rpm and heated to 70°C. A ~450g / L NaCIO3 solution was made using 22.53 g NaClOa in 50 ml demineralized water. Once at 70°C, 3.5 mL of NaCIO3 solution was added at a rate of approximately 0.15 mL / min. A peristaltic pump was set at 1 rpm to carry this out. The solution became a much darker brown colour and chlorine gas evolved. 45 minutes after completion of the NaClOa addition, the mixture was cooled to room temperature by turning off the hot plate and allowing slow cooling. No chlorine gas was visible at this point. The mixture was Buchner filtered through 0.45 pm cellulose nitrate filter paper to give the Pt containing liquor. The residual liquor was collected and weighed. This was bright yellow in colour. The CCM pieces, stirrer, temperature probe and spatulas used were all washed in demineralized water and the washings collected through the Buchner funnel. These washings were collected and weighed. These were pale yellow in colour. The residual CCM pieces were washed with distilled water and left to dry overnight on a watch glass. Results Within experimental error, 100% of the Pt from the CCM was recovered, the majority in the leach liquor with the remainder in the washings. In contrast, the leaching process did not result in any iridium being leached, highlighting the selectivity of this process. This methodology has been repeated with comparable results, indicating repeatability of the leaching process. This method thus shows repeatability and also selectivity for Pt leaching from CCMs. Base Metal Recovery Purification of PtCo and PtNi liquors after an oxidative leach using NaHCOs This specification is concerned with recovery of PGMs from waste catalyst coated membrane materials, including Pt / C, PtNi / C and PtCo / C catalysts, in order to obtain a full circular economy. However, the liquors produced from leaching the PtCo and PtNi catalysts contain base metal contaminants that need to be removed to produce a clean liquor. The aim of this experiment is to determine if adding NaHCOa to the liquors and increasing the pH to approximately 8 will cause the Co / Ni to precipitate such that they can be separated and recovered. If this method can remove the impurities, then it can form a purification process after leaching. Making up an NaHCOs solution An NaHCOa solution was made up to saturation (~100 g / L). In a beaker, with stirring at 100 rpm, 10 g of NaHCOa was weighed out and 100 ml of water added to it. The solution was heated to ~50 °C to aid with dissolving. Making up 25% NaOH solution To 75 mL of water in a beaker, 25 g of NaOH was added with stirring at 100 rpm. The solution was then transferred into a 100 mL volumetric flask and topped up to 100 mL. Purification Process 1. 50 mL of liquor was added to a beaker with a stirrer bar and temperature probe. The solution was stirred at 520 rpm. 2. 25% NaOH was added slowly (dropwise) to the solution and the pH recorded. NaOH was added until the pH reached approximately 3. 3. The was solution heated to 65 °C. 4. The required amount of NaHCOs solution was added slowly to the with stirring at 750 rpm and the pH measured with a pH probe until the solution reached a pH of between approximately 8 and 10. 5. The solution was cooled to room temperature. 6. Once cooled, the solution was filtered using a 0.45 pm cellulose nitrate filter paper and a Buchner funnel. 7. The liquor was collected and samples of liquor and solid were submitted for assay. 8. The liquor was then boiled and pH readjusted to pH -1 to 1 using 12 M HCI to get the correct PGM speciation for further processing. Results and Discussion Addition of solid bicarbonate resulted in a foamy, difficult to filter suspension. Analytical results show the solid addition was very successful at removing the contaminant base metal and a 98% decrease in base metal content from starting to purified liquor was shown. However, the method using solid bicarbonate addition resulted in a significant decrease in Pt content. Alternatively, on addition of bicarbonate as a saturated solution, a 50% decrease in Ni content was observed, with a much smaller loss of Pt. Although this method was not as successful at removing the base metal contaminant, the smaller loss in PGM content is advantageous and the process can be further optimised to target the base metal. In a further improvement, NaOH was used to raise the pH to ~3 before using bicarbonate to precipitate out the base metal. Bicarbonate is used to ensure particle size is large enough to filter as NaOH would precipitate out the base metals so quickly that the particle sizes would be very small and difficult to filter. This method resulted in a 100% decrease in Ni metal content and no decrease in Pt content. For PtCo solutions, analytical results showed an 85% decrease in Co content. In another experiment on a PtCo solution which was raised to a pH of 10,100% removal of Co was achieved. To avoid Pt removal, in one approach the residue and liquor are continuously separated when raising the pH, and then HCI is added prior to further processing. This reduces the amount of Pt being lost in the purification process. Overall, results indicate that these liquors can be purified by using a combination of NaOH / NaHCOa to raise the pH to "*8 and NaOH to raise the pH to ~10 to remove Ni and Co respectively, with little reduction / loss of Pt. This shows liquors contaminated with base metals can be successfully purified which is important in proving a full circular economy for Pt contained in fuel cell catalyst powders. Furthermore, the Ni and Co can be recovered for re-use. Ionomer Recovery 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. 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. 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. 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. 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. 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. Carbon recovery Certain fuel cell and electrolyser catalyst powders are deposited on a carbon support. Therefore, when the platinum group metals (PGMs) are removed, a carbon-based residue remains. To provide a full circular economy of all components contained within a fuel cell / electrolyser device, it is important to explore recycling routes for the carbon residue remaining after leaching. Oxidative leaching of carbon powders In these experiments two different carbon powders were leached under the same oxidative conditions as the catalyst powders and the residues sent for ICP analysis to understand any elemental changes in the carbon during leaching. Leaching using H2O2 1. 200 mL of 12 M HCI was added to a 3 neck, 500 mL round bottom flask with a condenser and temperature probe attached and magnetic stirrer bar. 2. The desired amount of H2O2 was then added to the vessel slowly with stirring to pre-oxidise the solution (1:2 molar ratio of metak^Oz). 3. The catalyst powder was then added to the vessel slowly. 4. The solution was heated to 70°C with stirring at 500 rpm. 5. Once the solution reached temp, it was left to heat at 70°C for 50 mins. 6. Solution was left to cool. 7. Once cooled, solution was filtered using a 0.45 pm cellulose nitrate filter paper and Buchner funnel. 8. The liquor and washings were collected in separated bottles and the mass of filter paper recorded. Leaching using NaCIOs 1. 200 mL of 6 M HCI was added to a 3 neck, 500 mL round bottom flask with a condenser and temperature probe attached and magnetic stirrer bar. 2. The desired amount of NaCIO3 (450 g / L NaCIO3) was then added to the vessel slowly with stirring at 500 rpm to pre-oxidise the solution (1:2 molar ratio of metal:NaCIO3). 3. The catalyst powder was then added to the vessel slowly. 4. The solution was heated to 70°C with stirring at 500 rpm. 5. Once solution reached temp, it was left to heat at 70°C for 50 mins. 6. Solution was left to cool. 7. Once cooled, solution was filtered using 0.45 pm cellulose nitrate filter paper and a Buchner funnel. 8. The liquor and washings were collected in separated bottles and the mass of filter paper recorded. Results and discussion Carbon support materials have been leached and ICP analysis of the liquors from leaching and residues obtained. The remaining solid carbon support materials can be analysed, e.g., with XPS, and compared to the carbon starting material to check changes to the structure and elemental composition of the carbon and QC for re-use. Characterization of leached carbon support materials Leached Pt / C and PtNi / C residues and their respective starting materials were sent for the following analysis: • ICP • XPS (with speciation - chlorine and oxygen) • Raman • P-XRD • CHN • LECO • Hg porosimetry • Nitrogen BET The aim of the analysis was firstly to understand if we had successfully recovered 100% of the PGMs via ICP and secondly understand what, if any, structural changes of the carbon support material occurred during leaching. This information can then be used to explore potential recycling routes, specifically understanding if a direct recycle process for the carbon support material is possible. The following results compare the Pt / C material to its equivalent material leached with HCI / H2O2. Elemental analysis of the two materials using CHN and XPS showed good agreement between techniques and to the ICP results. The results showed there was some residual Pt remaining and the chlorine content increased slightly after leaching, likely due to using HCI. An XPS spectra (Figure 7) was also recorded and showed the leached residue contained two overlapping doublets which corresponds to a metallic Pt doublet and a Pt oxide or chloride species. In XPS, elements appear as doublets, hence the single black doublet is the metallic Pt species in the starting material. The doublet on the left-hand side could be a Pt oxide or Pt chloride species, they overlap in the XPS spectra, however, more likely an oxide species due to the higher oxygen content in the elemental analysis. XRD analysis was carried out with the aim of understanding changes in carbon structure between the starting material and leached residue. Analysis of the leached residue showed that a small amount of amorphous carbon was present. Raman analysis (Figures 8(a) and 8(b)) was carried out and showed there were no substantial changes in carbon structure. The D band indicates defects in the material, while the G band indicates how graphitic the structure is, and their ratio indicates overall how defective the material is (larger ratio indicates a larger number of defects). Given the Raman spectra are identical, this suggested the acid leach treatment is not very aggressive towards the carbon and did not create any major defects. The peaks also remained narrow suggesting the material was not very amorphous. Nitrogen BET and Hg Porosimetry can be used to look at changes in pore size, distribution of pore sizes and change in hydrophobicity of the carbon. LECO can be used to determine the concentration of carbon, oxygen and hydrogen in the sample. The characterisation results indicate that the carbon is undamaged by the oxidative leach conditions. Leached carbon material which is within specification in terms of structural and elemental composition after leaching can be directly recycled. Additionally, if small structural / elemental changes do occur, a heat or chemical treatment can restore functionality sufficiently for the material to be reused as a carbon support or at least blended with fresh material to make a mixed support. Chemical improvement of the carbon residue can be used to recycle carbon powder. For example, an oxidation reduction method has been used to recover carbon powder. Graphite oxide was generated from graphite by addition of potassium permanganate to a solution of graphite (carbon powder), phosphoric acid and sulphuric acid. The solution was stirred in an ice bath and then heated to 50 °C for 12 h. Ice water and hydrogen peroxide were then added to the solution. Finally, the system was centrifuged, and the solid products obtained were washed with hydrochloric acid and distilled water until pH 7 was reached to produce graphene oxide. To convert graphene oxide to graphene, the oxide was mixed with ammonia water until pH 8 was reached and then mixed with vitamin C to act as the reducing agent. Alternatively, the carbon residue can be subjected to a high temperature thermal treatment to destroy organics and increase absorptive capacity of the carbon. For example, this approach can be used on the carbon waste stream generated from the leaching processes to make an activated carbon suitable for filtration applications. 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 and at least one catalyst comprising platinum, palladium and / or ruthenium on a carbon support material, 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 with the carbon support material remaining in solid form, the solution then being 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 separate and recover the ionomer dispersion from the solid carbon support material, wherein the dispersion of ionomer is performed before or after the leaching of the platinum, palladium and / or ruthenium in step (a);(c) processing the solution comprising leached platinum, palladium and / or ruthenium to separate base metal contamination and recover the platinum, palladium and / or ruthenium; and(d) after steps (a) and (b) in which both the ionomer and the platinum, palladium and / or ruthenium are separated from the carbon support material, the remaining solid carbon support material is recovered for re-use.

2. A method according to claim 1,wherein the carbon support material is in the form of a particulate carbon powder and the platinum, palladium and / or ruthenium is disposed on the particles of carbon powder.

3. A method according to claim 1 or 2,wherein the at least one catalyst comprising platinum, palladium and / or ruthenium on a carbon support material is platinum-on-carbon, platinum-cobalt-on-carbon, or platinum-nickel-on-carbon.

4. A method according to any preceding claim,wherein in step (c), after leaching the platinum, palladium and / or ruthenium and separating the solution from remaining solid components of the waste catalyst coated membrane material, the solution is treated with a base to increase the pH of the solution such that the base metal, optionally including cobalt and / or nickel, in the solution is precipitated and separated from the solution, optionally via filtration.

5. A method according to claim 4,wherein the base comprises one or both of NaHCOs and NaOH.

6. A method according to claim 4 or 5,wherein the pH of the solution is increased to between 7.5 and 10.

7. A method according to any of claims 4 to 6,wherein, after precipitating and separating the base metal, the solution is reacidified and the platinum, palladium and / or ruthenium is recovered as a salt or PGM sponge.

8. A method according to any preceding claim,wherein in step (d) the remaining solid carbon support material is washed and dried prior to being re-used.

9. A method according to any preceding claim,wherein the solid carbon support material is re-used as a carbon support material in the manufacture of new catalyst material comprising platinum, palladium and / or ruthenium on the carbon support material or re-used as an activated carbon material.

10. A method according to claim 9,wherein the recovered carbon support material is blended with fresh carbon support material when re-used to manufacture the new catalyst material.

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

12. 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.

13. 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.

14. 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 12 M, 10 M, 7 M, 6.5 M, or 6 M; or within a range defined by any combination of the aforementioned lower and upper limits.

15. 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.

16. 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 or a waste catalyst ink material comprising ionomer.18

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