Recycling of waste catalyst coated membrane components

Abstract

A method of recycling a waste ionomer material, the method comprising: heating the waste ionomer material in a solvent to disperse the waste ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing fluoride anions in solution; contacting the dispersion with a precipitant or adsorbent to form a solid material comprising the fluoride anions; and separating the dispersion of ionomer from the solid material comprising the fluoride anions.

Description

[0001] RECYCLING OF WASTE CATALYST COATED MEMBRANE COMPONENTS

[0002] Field

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

[0004] Background

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

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

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

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

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

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

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

[0012] One current method to recover PGMs from production scrap and end-of-life CCM material involves incineration. The incineration process yields a PGM rich (typically Pt and Ir) ash which is processed via conventional PGM refining routes. However, the incineration process releases harmful and toxic gases such as CO2 and HF from the polymers that are part of the membrane. Both these gases have negative impacts as they pollute the atmosphere, increase the greenhouse effect, and / or have harmful effects in the human body. As such, there is a need for a cleaner process which reduces or eliminates the emission of these gases.

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

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

[0015] Summary of Invention

[0016] The present specification is concerned with providing a method of recycling a waste ionomer material such as waste ionomer membrane, catalyst-coated ionomer membrane, or catalyst layer material containing ionomer. As described in the background section, such materials are key components of fuel cells and hydrogen producing water electrolysers and typically may contain platinum group metal catalyst material.

[0017] In order to recover ionomer from such materials, the waste ionomer material can be heated in a solvent to disperse the waste ionomer material forming a dispersion of ionomer which can be separated and recovered.

[0018] However, the present inventors have found that the process of heating the waste ionomer material in the solvent to form the dispersion can generate unwanted fluoride anions due to breakdown of ionomer. Fluoride is an unwanted product as it has considerable health and safety risks and degrades processing apparatus. The presence of fluoride in the recycled ionomer stream is considered a barrier to reuse of the ionomer. Without its removal, the ionomer may not be able to be reused, as fluoride may cause further problems in end applications when reused.

[0019] It has been found that the formation of fluoride anions during the ionomer dispersion process is particularly problematic when platinum group metal catalyst material is present during the dispersion process. It has been found that such platinum group metal catalyst material promotes ionomer breakdown and fluoride generation during the ionomer dispersion process. One possibility for reducing this breakdown mechanism and fluoride generation is to remove platinum group metal material prior to performing the ionomer dispersion process. For example, platinum group metal can be leached from waste ionomer material using an oxidative and / or reductive acid leach prior to performing the ionomer dispersion process. However, some contaminant platinum group metal material may remain after such leaching processes which could promote ionomer breakdown and fluoride generation during subsequent ionomer dispersion. Even if substantially all the platinum group metal is removed, there may still be the possibility that fluoride is present in small amounts when there is substantially no precious metal catalyst present. That said, the present inventors have found that they can substantially eliminate the fluoride issue by implementing highly efficient platinum group metal leaching methodologies to remove platinum group metal catalyst materials prior to ionomer dispersion.

[0020] Despite the above-described possibility of avoiding fluoride formation via leaching of platinum group metal material prior to ionomer dispersion, there may be circumstances in which it would be useful to disperse, separate, and recover the ionomer prior to processing and recovering the platinum group metal material. In such approaches, generation of fluoride during ionomer dispersion in the presence of platinum group metal has been found to be a significant issue.

[0021] In light of the above, the present specification provides a method of recycling a waste ionomer material, the method comprising: heating the waste ionomer material in a solvent to disperse the waste ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing fluoride anions in solution; contacting the dispersion with a precipitant or adsorbent to form a solid material comprising the fluoride anions; and separating the dispersion of ionomer from the solid material comprising the fluoride anions.

[0022] The precipitant can be a metal compound which reacts with the fluoride anions in solution to form a solid metal fluoride salt which is precipitated from solution. For example, such a metal compound can be selected from one or more of: an alkaline earth metal compound; a calcium compound; a magnesium compound; a strontium compound; a transition metal compound; a titanium compound; a post-transition metal compound; an aluminium compound; a hydroxide. Examples include calcium hydroxide and magnesium hydroxide. The precipitated metal fluoride can then be separated from the dispersion via filtration or centrifugation.

[0023] As an alternative to precipitation, the fluoride anions can be removed from the dispersion by using an adsorbent which is capable of adsorbing anions (via, for example, physical adsorption, ionic bonding, or covalent bonding of fluoride). Such adsorbents are known in water treatment applications as described in "A comprehensive review of adsorbents for fluoride removal from water: performance, water quality assessment and mechanism", Environmental Science: Water Research & Technology (RSC Publishing) D0l:10.1039 / D1EW00232E. The adsorbent may be a solid, insoluble metal compound which adsorbs fluoride anions. The solid metal compound may be selected from one or more of: a metal oxide; magnesium oxide; calcium oxide; aluminium oxide; titanium oxide; a mixed metal oxide. Such an adsorbent can be introduced into the reaction vessel in which the waste ionomer material is dispersed (e.g., as solid particles, a solid bar or rod, or as a bag of adsorbent material) or alternatively the dispersion of ionomer containing fluoride anions can be passed through a bed of the adsorbent after the ionomer dispersal step (e.g., a bed of adsorbent in a HF resistant vessel such as a PTFE lined vessel).

[0024] The present specification thus recognises that: (i) fluoride anions are generated during dispersion of waste ionomer material, particularly in the presence of platinum group metal; (ii) that such fluoride anions in the waste ionomer recycling feed are problematic in terms of health and safety, processing equipment degradation, and suitability for re-use of the ionomer material; and (iii) that the fluoride generated in the waste ionomer recycling feed can be effectively removed by treatment with a precipitant or adsorbent to form a solid material comprising the fluoride which can then be easily separated from the ionomer dispersion, e.g., via filtration. The recycling methodology is particularly useful for waste ionomer materials which comprise at least one platinum group metal catalyst material. Such materials may include ionomer membranes (which may have recombination catalysts disposed therein), catalyst-coated ionomer membrane, and / or catalyst layer materials containing ionomer (which may be derived, for example, by removal of the catalyst layer material from catalyst-coated ionomer membrane). Furthermore, the waste ionomer material may be scrap (e.g., manufacturing scrap) or used (e.g., end-of-life) ionomer material from a fuel cell or electrolyser application.

[0025] In relation to the above, it has been noted that purification processes such as ultrafiltration are utilized during ionomer manufacture (see, for example, WO2022224105). Furthermore, fluoride removal from water by precipitation using calcium hydroxide, for example, is already established in water purification and other industries. Such examples include CN105384316B (electronics) and US9469549B2 (solar cell manufacture). However, as far as the present inventors are aware, the problem of fluoride generation during waste ionomer recycling, particularly in the presence of platinum group metal materials, has not been identified and there is no suggestion of the present methodology as applied in the recycling of waste ionomer materials to address this problem.

[0026] Brief Description of the Drawings

[0027] 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:

[0028] Figure 1 shows a waste ionomer recycling process according to the present specification;

[0029] Figure 2 shows a more detailed example of a waste ionomer recycling process according to the present specification;

[0030] Figure 3 shows another example of a waste ionomer recycling process in which platinum group metals are leached from the waste ionomer material prior to ionomer dispersion and subsequent treatment of the ionomer dispersion to remove any fluoride generated during the dispersion process;

[0031] Figure 4 shows another example of a waste ionomer recycling process in which ionomer is dispersed and separate from platinum group metal material, the remaining platinum group metal material is leached to recover platinum group metal, and the ionomer dispersion is treated to remove fluoride generation during the dispersion process, the fluoride removal being particularly useful in this example as the platinum group metal present during the ionomer dispersal step promotes fluoride generation;

[0032] Figure 5 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;

[0033] Figure 6 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;

[0034] Figure 7 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 8 shows a further step of autoclaving the membrane to disperse the membrane in water following the treatment process as shown in Figure 6; and

[0035] Figure 9 shows a further step (post-autoclave) of ion exchange to convert the dispersed polymer salt back to protonated acid form.

[0036] Detailed Description

[0037] As described in the summary section and illustrated in Figure 1, the present specification provides a method of recycling a waste ionomer material, the method comprising: heating the waste ionomer material in a solvent to disperse the waste ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing fluoride anions; contacting the dispersion with a precipitant or adsorbent to form a solid material comprising the fluoride anions; and separating the dispersion of ionomer from the solid material comprising the fluoride anions. After separating the solid fluorine- containing material from the ionomer dispersion, any remaining metal in the dispersion (from the precipitant or adsorbent) can be removed, e.g., via ion exchange.

[0038] As also described in the summary section, the precipitant can be a metal compound which reacts with the fluoride anions in solution to form a solid metal fluoride salt which is precipitated from solution. For example, such a metal compound can be selected from one or more of: an alkaline earth metal compound; a calcium compound; a magnesium compound; a strontium compound; a transition metal compound; a titanium compound; a post-transition metal compound; an aluminium compound; a hydroxide. Examples include calcium hydroxide and magnesium hydroxide. The precipitated metal fluoride can then be separated from the dispersion via filtration or centrifugation.

[0039] As an alternative to precipitation, the fluoride anions can be removed from the dispersion by using an adsorbent which is capable of adsorbing anions (via, for example, physical adsorption, ionic bonding, or covalent bonding of fluoride). Such adsorbents are known in water treatment applications as described in "A comprehensive review of adsorbents for fluoride removal from water: performance, water quality assessment and mechanism", Environmental Science: Water Research & Technology (RSC Publishing) D0l:10.1039 / D1EW00232E. The adsorbent may be a solid, insoluble metal compound which adsorbs fluoride anions. The solid metal compound may be selected from one or more of: a metal oxide; magnesium oxide; calcium oxide; aluminium oxide; titanium oxide; a mixed metal oxide. Such an adsorbent can be introduced into the reaction vessel in which the waste ionomer material is dispersed (e.g., as solid particles, a solid bar or rod, or as a bag of adsorbent material) or alternatively the dispersion of ionomer containing fluoride anions can be passed through a bed of the adsorbent after the ionomer dispersal step (e.g., a bed of adsorbent in a HF resistant vessel such as a PTFE lined vessel).

[0040] The solvent used to disperse the ionomer can be selected from water, an aqueous basic solution, an organic solvent, an alcohol, or a mixture thereof, e.g., 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. Furthermore, the waste ionomer material can be heated for: at least 15 minutes, 30 minutes, 1 hour, 2 hours, or 3 hours; no more than 72 hours, 48 hours, 24 hours, 10 hours, 6 hours, or 4 hours; or within a range defined by any combination of the aforementioned lower and upper limits. These process conditions are suitable for dispersing the waste ionomer material but also lead to generation of some fluoride, particularly if platinum group metal catalyst materials are present during the process, hence the need for a treatment step to remove fluoride after ionomer dispersal.

[0041] The waste ionomer material may also comprise one or both of a carbon catalyst support material and a membrane reinforcement material. In this case, the carbon catalyst support material and / or the membrane reinforcement material can be separated from the dispersion with the precipitated or adsorbed fluoride.

[0042] In one preferred methodology, the waste ionomer material is converted to salt form prior to or during heating to disperse the waste ionomer material. Preferably, the waste ionomer material is converted to salt form without dispersing the waste ionomer material. For example, the waste ionomer material can be converted to salt form by treatment with an aqueous basic solution. Excess base can then be removed. Subsequently, the ionomer can be dispersed by heating in a solvent and, after dispersal of the ionomer, the ionomer dispersion can be treated to precipitate / adsorb and remove fluoride. The ionomer can then be subjected to an ion exchange process to re-protonate the ionomer in the dispersion. The ion exchange process used to re-protonate the ionomer may also be used to remove any remaining metal in the dispersion or separate ion exchange processes may be used to re- protonate the ionomer and remove any remaining metal.

[0043] In relation to the above, it has been found that converting the ionomer to salt form prior to dispersing the ionomer is advantageous to achieve good dispersion of the ionomer material while reducing damage to the ionomer material. As previously indicated, damage to the ionomer can be further reduced by removing the PGM material, or at least a majority of the PGM material, prior to the ionomer dispersal process. To the extent that any ionomer is degraded to generate fluoride anions, this is addressed by treatment to precipitate / adsorb and remove the fluoride from the ionomer dispersion as described herein.

[0044] As such, one process flow as illustrated in Figure 2 is as follows: (i) treatment of the waste ionomer material with a base to form a solid ionomer salt material; (ii) heating the solid ionomer salt material in a solvent to form a dispersion of the ionomer salt material; (iii) contacting the dispersion with a precipitant or adsorbent to form a solid material comprising the fluoride anions; (iv) separating the dispersion of ionomer from the solid material comprising the fluoride anions; (v) removing any remaining metal ions in the dispersion (e.g., via ion exchange); and (vi) subjecting the ionomer dispersion to an ion exchange process to re-protonate the ionomer material (which may be a separate step or combined with step (v).

[0045] The recycling methodology is particularly useful for waste ionomer materials which comprise at least one platinum group metal catalyst material since it has been found that platinum group metal catalyst material promotes ionomer degradation and fluoride generation during the ionomer dispersion process. Such materials may include ionomer membranes (which may have recombination catalysts disposed therein), catalyst-coated ionomer membrane (i.e., ionomer membrane coated with PGM catalyst materials), and / or catalyst layer materials containing ionomer (which may be derived, for example, by removal of the catalyst layer material from catalyst-coated ionomer membrane prior to further processing to recover catalyst and ionomer materials). Furthermore, the waste ionomer material may be scrap (e.g., manufacturing scrap) or used (e.g., end-of-life) ionomer material from a fuel cell or electrolyser application.

[0046] Figure 3 shows a process flow in which platinum group metal is removed from the waste ionomer material prior to ionomer dispersion and treatment of the ionomer dispersion to precipitate and separate fluoride material. In this case, the removal of the platinum group metal material prior to ionomer dispersion reduces the amount of fluoride which is generated during dispersion and thus fluoride precipitation / adsorption is only required to extract any small quantities of fluoride which may be present in the waste ionomer stream. In the illustrated example, an oxidative acid leach is used to extract platinum (and / or palladium and / or ruthenium) from the waste ionomer material and, if iridium is present in the material, a reductive acid leach is used to extract the iridium.

[0047] In contrast, Figure 4 shows a process flow in which platinum group metal is not removed from the waste ionomer material prior to ionomer dispersion. In this case, it has been found that significant quantities of fluoride are generated during dispersion promoted by the platinum group metal material. Accordingly, the use of a precipitant / adsorbent to extract the significant quantities of fluoride from the waste ionomer stream following this approach can be critical to avoid down-stream processing issues. After separating the platinum group metal material from the ionomer dispersion, the platinum group metal material can be subjected to leaching processes as discuses in relation to Figure 3 for extracting platinum and iridium.

[0048] 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.

[0049] For the oxidative acid leach of platinum (and / or palladium and / or ruthenium), 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 electrolytical ly 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, palladium and / or ruthenium 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, 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.

[0050] Separation of the solution containing the leached platinum, palladium and / or ruthenium may be achieved via filtration or centrifugation. The separated solution may be concentrated by boiling the solution down to a suitable PGM concentration for further processing. Alternatively, the leachate can be recirculated to leach more platinum, palladium and / or ruthenium from further waste catalyst coated membrane material, recirculation being repeated as required until a suitable or target concentration of platinum, palladium and / or ruthenium is reached. For example, after separating the solution containing the leached platinum, palladium and / or ruthenium 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.

[0051] 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.

[0052] 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 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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, advantageously the Pt (and / or palladium and / or ruthenium) is removed first by oxidative leaching prior to applying the reductive leach to recover the iridium.

[0057] Examples

[0058] PGM recovery

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Ir reductive leach

[0064] 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.

[0065] 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.

[0066] Pt oxidative leach (repeated)

[0067] 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.

[0068] Ir reductive leach (repeated)

[0069] 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.

[0070] Results Discussion and Conclusions

[0071] 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.

[0072] Ionomer Recovery

[0073] 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.

[0074] Figure 5 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.

[0075] Figure 6 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 6, the solid polymer salt membrane material was washed in water to remove any residual LiOH solution.

[0076] Figure 7 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.

[0077] Figure 8 shows a further step of autoclaving the membrane to disperse the membrane in water following the treatment process as shown in Figure 6. 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.

[0078] The aqueous dispersion of the polymer (ionomer) salt is then subjected to treatment with a precipitant or adsorbent (e.g., a precipitant such as calcium hydroxide) to precipitate / adsorb any fluoride from the dispersion (e.g., as calcium fluoride), which is then removed, e.g., via filtration.

[0079] In one example, calcium hydroxide (75 mg, 1.0 mmol) was added to an ionomer dispersion (6 mL) recycled via high temperature aqueous processing as described above. The fluoride content of the dispersion was reduced from around 190 pg / mL to around 40 pg / mL. The use of more calcium hydroxide reduces the fluoride content further. The solid calcium product is then removed by solidliquid separation such as filtration. Any undesired calcium in the dispersion is removed by ion exchange.

[0080] The aqueous dispersion of the polymer (ionomer) salt can also be subjected to a filtration process to separate the ionomer dispersion from solid carbon catalyst support and solid polytetrafluoroethylene membrane reinforcement material. These materials may be separated in the same step used to remove the precipitated calcium fluoride or these materials may be separated prior to precipitating and removing the fluoride from the ionomer dispersion.

[0081] Figure 9 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. Ion exchange can also be used to remove any remaining calcium from the ionomer dispersion. Summary

[0082] 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. The present specification particularly addresses issues caused by fluoride generation during the recycling process to ensure that the process is safer, equipment is protected, and the resultant ionomer product material is not contaminated with fluoride and thus better suited for re-use.

[0083] While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Claims1. A method of recycling a waste ionomer material, the method comprising: heating the waste ionomer material in a solvent to disperse the waste ionomer material forming a dispersion of ionomer in the solvent, the dispersion also containing fluoride anions in solution; contacting the dispersion with a precipitant or adsorbent to form a solid material comprising the fluoride anions; and separating the dispersion of ionomer from the solid material comprising the fluoride anions.

2. A method according to claim 1, wherein the precipitant is a metal compound which reacts with the fluoride anions in solution to form a solid metal fluoride salt which is precipitated from solution.

3. A method according to claim 2, wherein the metal compound is selected from one or more of: an alkaline earth metal compound; a calcium compound; a magnesium compound; a strontium compound; a transition metal compound; a titanium compound; a post-transition metal compound; an aluminium compound; a hydroxide.

4. A method according to claim 2 or 3, wherein the precipitated metal fluoride is separated from the dispersion via filtration or centrifugation.5 A method according to claim 1, wherein the adsorbent is a solid, insoluble metal compound which adsorbs fluoride anions.

6. A method according to claim 5, wherein the solid metal compound is selected from one or more of: a metal oxide; magnesium oxide; calcium oxide; aluminium oxide; titanium oxide; a mixed metal oxide.

7. A method according to claim 5 or 6,wherein the adsorbent is introduced into a reaction vessel in which the waste ionomer material is dispersed or the dispersion of ionomer containing fluoride anions is passed through a bed of the adsorbent.

8. A method according to any preceding claim, wherein the waste ionomer material comprises at least one platinum group metal catalyst material during heating of the waste ionomer material.

9. A method according to any preceding claim, wherein the waste ionomer material is an ionomer membrane, a catalyst-coated ionomer membrane, or a catalyst layer material containing ionomer.

10. A method according to any preceding claim, wherein the waste ionomer material is scrap or used ionomer material from a fuel cell or electrolyser application.

11. A method according to any preceding claims, wherein the solvent is water, an aqueous basic solution, an organic solvent, an alcohol, or a mixture thereof.

12. A method according to any preceding claims, wherein, after separating the solid material comprising the fluoride anions from the dispersion, any remaining metal species in the dispersion from the precipitant or adsorbent is removed, optionally via ion exchange.

13. A method according to any preceding claims, wherein the waste ionomer material is heated to 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 preceding claims, wherein the waste ionomer material is heated for: at least 15 minutes, 30 minutes, 1 hour, 2 hours, or 3 hours; no more than 72 hours, 48 hours, 24 hours, 10 hours, 6 hours, or 4 hours; or within a range defined by any combination of the aforementioned lower and upper limits.

15. A method according to any preceding claims, wherein the waste ionomer material is converted to salt form prior to or during heating to disperse the waste ionomer material.

16. A method according to claim 15, wherein the waste ionomer material is converted to salt form by treatment with an aqueous basic solution.

17. A method according to claim 15 or 16, wherein after dispersing the waste ionomer material, the salt form of ionomer is converted back to protonated acid form by ion exchange.

18. A method according to any preceding claim, wherein the waste ionomer material comprises one or both of a carbon catalyst support material and a membrane reinforcement material, and the carbon catalyst support material and / or the membrane reinforcement material is separated from the dispersion with the precipitated or adsorbed fluoride.

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