Hydrocarbon membrane

Abstract

The disclosure provides a process of preparing an ion-conducting membrane comprising a sulphonated hydrocarbon ionomer having an ion-exchange capacity I2 meq / g, the process comprising the steps of: a) providing a sulphonated hydrocarbon ionomer having an ion- exchange capacity I1 meq / g; b) casting an ion-conducting membrane from a mixture of the sulphonated hydrocarbon ionomer provided in step a) and a solvent; c) applying a treatment to the ion-conducting membrane prepared in step b) which reduces the ion-exchange capacity from I1 meq / g to an ion-exchange capacity I2 meq / g, wherein I2 is less than I1.

Description

[0001] Hydrocarbon membrane

[0002] Field of the Invention

[0003] This disclosure relates to ion-conducting membranes containing sulphonated hydrocarbon ionomers, and methods for the preparation thereof. In particular, this disclosure relates to proton exchange membranes, and processes of manufacturing the same. The ionconducting membranes can be suitable for use in electrochemical devices such as fuel cells and / or electrolysers.

[0004] Background of the Invention

[0005] A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. A fuel, e.g. hydrogen, an alcohol such as methanol or ethanol, or formic acid, is supplied to the anode and an oxidant, e.g. oxygen or air, is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.

[0006] Fuel cells are usually classified according to the nature of the electrolyte employed. Often the electrolyte is a solid polymeric membrane, in which the membrane is electronically insulating but ionically conducting. In the proton exchange membrane fuel cell (PEMFC) the membrane is proton conducting, and protons, produced at the anode, are transported across the membrane to the cathode, where they combine with oxygen to form water.

[0007] An electrolyser is an electrochemical device for electrolysing water to produce high purity hydrogen and oxygen. Electrolysers can operate in both alkaline and acidic systems. Those electrolysers that employ a solid proton-conducting polymer electrolyte membrane, or proton exchange membrane (PEM), are known as proton exchange membrane water electrolysers (PEMWEs).

[0008] Traditionally, perfluorosulphonic acid (PFSA) ionomers are used in proton exchange membranes due to their long-proven favourable properties in terms of membrane performance and durability, as well as manufacturability. However, hydrocarbon-based ionomers are actively sought as an alternative to PFSA ionomers due to, for example, environmental concerns relating to fluoro-chemicals.

[0009] Many different hydrocarbon ionomers have been investigated, with significant focus on those incorporating aromatic groups as part of the polymer main chain, such as sulphonated derivatives of poly(arylene ether)s, poly(arylene ether ketone)s, poly(arylene sulphone)s, poly(imide)s, poly(benzimidazole)s, polyphenylenes and phenylated polyphenylenes. However, membranes to date made from hydrocarbon ionomers do not meet the threshold of performance and manufacturability required for commercial membrane products. In particular, hydrocarbon ionomers consistently display lower dispersion limits when compared to the PFSA incumbent and a smaller range of suitable casting solvents.

[0010] Summary of the Invention

[0011] Accordingly, the present disclosure provides a process of preparing an ion-conducting membrane comprising a sulphonated hydrocarbon ionomer having an ion-exchange capacity I2 meq / g, the process comprising the steps of: a) providing a sulphonated hydrocarbon ionomer having an ion-exchange capacity meq / g;b) casting an ion-conducting membrane from a mixture of the sulphonated hydrocarbon ionomer provided in step a) and a solvent; c) applying a treatment to the ion-conducting membrane prepared in step b) which reduces the ion-exchange capacity from meq / g to an ion-exchange capacity I2 meq / g, wherein I2 is less than .

[0012] The identity of the sulphonated hydrocarbon ionomer remains the same throughout the process, apart from the reduction in ion-exchange capacity, which corresponds with a reduction in the amount of sulphonate groups in the hydrocarbon ionomer.

[0013] The inventors have found that ionomers with higher ion-exchange capacity are more processable and can be more readily cast to form membranes. However, ionomers with a lower ion-exchange capacity are often desirable in ion-conducting membranes. Surprisingly, ion-conducting membranes can be made with such high ion-exchange capacity ionomers before being subjected to a treatment which reduces the ion-exchange capacity without damaging the membrane, thus improving durability. So, effective hydrocarbon ionomer-based membranes can be prepared by easy to carry out, conventional, membrane casting techniques.

[0014] The present disclosure also provides a process of preparing a catalyst-coated membrane for a fuel cell or a water electrolyser, the catalyst-coated membrane comprising a catalyst layer on a face of an ion-conducting membrane, the process comprising: i) preparing an ion-conducting membrane by a process as defined in this disclosure; ii) preparing a catalyst layer; wherein either the catalyst layer is prepared and the ion-conducting membrane is applied to the catalyst layer, or the ion-conducting membrane is prepared and the catalyst layer is applied to the ion-conducting membrane.

[0015] The advantageous process of the disclosure is particularly suitable for so called additive layer-type processes for preparing catalyst-coated membranes in which the catalyst- coated membrane is built up layer by layer. It is also particularly suitable for direct-to- membrane printing of catalyst layers.

[0016] Brief Description of the Drawings

[0017] Figure 1 shows FT-IR spectra comparing ion-conducting membranes which have and have not undergone a treatment step c) as defined herein.

[0018] Figure 2 is chart showing the decrease in water uptake of ion-conducting membranes after undergoing a treatment step c) as defined herein.

[0019] Figure 3 is chart showing the decrease in water uptake of further ion-conducting membranes after undergoing a treatment step c) as defined herein.

[0020] Figure 4 is chart showing the decrease in dimensional change from dry state to wet state of ion-conducting membranes after undergoing a treatment step c) as defined herein.

[0021] Figure 5 is chart showing the decrease in dimensional change from dry state to wet state of further ion-conducting membranes after undergoing a treatment step c) as defined herein.

[0022] Figure 6 is a chart with the data shown in Figs. 3 and 5 in terms of percentage mass change and percentage change in the in-plane (x) dimension.

[0023] Figure 7 is a chart showing ion-exchange capacity of ion-conducting membranes after undergoing a treatment step c) as defined herein.

[0024] Figure 8 is a chart correlating ion-exchange capacity after a treatment step c) as defined herein with dimensional change from dry state to wet state. Figure 9 is a chart with thermogravimetric analysis data showing the mass loss steps, attributable to water loss and loss of sulphonate groups, for sulphonated hydrocarbon ionomers undergoing a heat treatment step.

[0025] Figure 10 is a chart with thermogravimetric analysis data showing the mass loss steps, attributable to water loss and loss of sulphonate groups, for sulphonated hydrocarbon ionomers undergoing a heat treatment step.

[0026] Detailed Description

[0027] The ion-conducting membrane is accordingly a hydrocarbon membrane, i.e. it does not comprise fluorinated ionomer. An ionomer is a polymer composed of repeating units of both electrically neutral repeating units and ionized units covalently bonded to the electrically neutral repeating units as pendant moieties. In a hydrocarbon ionomer, the electrically neutral repeating units are hydrocarbon based, and do not comprise fluorine substituents. In a sulphonated hydrocarbon ionomer, the ionized units are sulphonate moieties. Suitably, the sulphonated hydrocarbon ionomer is selected from sulphonated derivatives of poly(arylene ether)s, poly(arylene ether ketone)s, poly(arylene sulphone)s, poly(imide)s, poly(benzimidazole)s, polyphenylenes and phenylated polyphenylenes. Typically, the sulphonated hydrocarbon ionomer is a sulphonated polyphenylene hydrocarbon ionomer. The sulphonated polyphenylene hydrocarbon ionomer is a linear sulphonated polyphenylene, a kinked sulphonated polyphenylene, a side-chain sulphonated polyphenylene or a sulphonated phenylated polyphenylene hydrocarbon ionomer. Such motifs are known to the skilled person, for example as described in “On the evolution of sulfonated polyphenylenes as proton exchange membranes for fuel cells", Mater. Adv. 2021 , 2, pp 4966-5005. More typically, the sulphonated hydrocarbon ionomer is a sulphonated phenylated polyphenylene hydrocarbon ionomer, for example the Pemion™ range of sulphonated hydrocarbon ionomers from lonomr Innovations. The sulphonated phenylated polyphenylene hydrocarbon ionomer may be linear or branched.

[0028] The sulphonated phenylated polyphenylene hydrocarbon ionomer typically comprises a core repeating unit comprising a sulphonated moiety comprising at least three aryl and / or heteroaryl groups which are linked by carbon-to-carbon single bonds. Typically, the core repeating unit comprises no more than ten, more typically no more than nine aryl and / or heteroaryl groups. Typically, the core repeating unit comprises at least five aryl and / or heteroaryl groups. The core repeating unit may comprise nine aryl and / or heteroaryl groups and may be obtainable by the cycloaddition reaction of a sulphonated bistetracyclone moiety with diphenylacetylene, for example as described in Mater. Adv. 2021 , 2, pp 4966-5005 as well as “Structurally-Defined, Sulfo-Phenylated, Oligophenylenes and Polyphenylenes", J. Am. Chem. Soc., 2015, 137, pp12223-12226, and WO 2018 / 187864 which is incorporated herein by reference in its entirety. The repeating unit may further comprise a linking group comprising heteroaryl and / or aryl groups, typically at least one and no more than ten, more typically no more than seven such groups. Suitably, the linking group comprises one or more phenyl groups, typically only phenyl groups. Suitably, the linking group comprises one or more naphthyl groups. Suitably, the linking group comprises one or more pyridyl groups.

[0029] The sulphonated phenylated polyphenylene hydrocarbon ionomer may also comprise a core hydrophobic repeating unit, which does not comprise sulphonate moieties and which may comprise at least three aryl and / or heteroaryl groups which are linked by carbon-to- carbon single bonds. Typically, the core repeating unit comprises no more than ten, more typically no more than nine aryl and / or heteroaryl groups. Typically the core repeating unit comprises at least five aryl and / or heteroaryl groups. The core repeating unit may comprise nine aryl and / or heteroaryl groups and may be obtainable by the cycloaddition reaction of a bistetracyclone moiety with diphenylacetylene, for example as described in WO 2018 / 187864 which is incorporated herein by reference in its entirety. This hydrophobic repeating unit may further comprise a linking group comprising heteroaryl and / or aryl groups, typically at least one and no more than ten, more typically no more than seven such groups. Suitably, the linking group comprises one or more phenyl groups, typically only phenyl groups. Suitably, the linking group comprises one or more naphthyl groups. Suitably, the linking group comprises one or more pyridyl groups.

[0030] The molar ratio of the repeating unit comprising a sulphonated moiety and the hydrophobic repeating unit may be in the range of and including about 1 :99 to about 99: 1 . The sulphonated hydrocarbon ionomer may be a block copolymer comprising a first block having a repeating unit comprising a sulphonated moiety as defined above, and a second block having a second repeating unit comprising a hydrophobic repeating unit as defined above. The number of repeating units comprising a sulphonated moiety in the first block may be in the range of and including about three to about one hundred, and the number of repeating units comprising a hydrophobic repeating unit in the second block may be in the range of and including about three to about one hundred.

[0031] The sulphonated hydrocarbon ionomer provided in step a) has an ion-exchange capacity meq / g. The hydrocarbon ionomer provided in step a) has more sulphonate groups than the hydrocarbon ionomer in the ion-conducting membrane after step c) of the process. Accordingly, it contains sacrificial sulphonate groups, which can be removed by a treatment which is preferably a heat treatment step as defined herein. Put another way, the ionomer having an ion-exchange capacity meq / g provided in step a) has its ion-exchange capacity reduced to I2 meq / g by the treatment, and the treatment causes this reduction of ion-exchange capacity. The sacrificial sulphonate groups may be connected to the hydrocarbon ionomer by carbon-to-sulphur bonds as is conventional. For example, in a phenylated polyphenylene hydrocarbon ionomer the sulphonate groups may be connected to phenyl groups by carbon- to-sulphur bonds. The temperature required for thermal decomposition can be altered, for example, by adding particular counter-ions (e.g. Na, Ca counter-ions etc). Alternatively, the sulphonate groups may be connected to the hydrocarbon ionomer via linking groups which facilitate removal of the sulphonate groups by a treatment, preferably a heat treatment. Alternative treatments may be, for example, UV curing (photo-degradation), oxidation, hydrolysis, pyrolysis or bio-degradation. The number of sulphonate groups in the hydrocarbon ionomer provided in step a) can be controlled via the synthetic process used to prepare the hydrocarbon ionomer. For example, by using synthetic precursors with an appropriate level of sulphonation. For example, the level of sulphonation in the precursors used to make phenylated polyphenylene hydrocarbons in a process such as the processed disclosed in WO 2018 / 187864, which is incorporated herein by reference in its entirety, and “On the evolution of sulfonated polyphenylenes as proton exchange membranes for fuel cells", Mater. Adv. 2021 , 2, pp 4966-5005. may suitably be greater than or equal to about 4 meq / g, suitably greater than or equal to about 5 meq / g, typically greater than or equal to about 7 meq / g. may suitably be any value which is greater than I2 and provides an ionomer which is processable in the desired conditions, e.g. can be effectively mixed with and cast from the desired solvent. The treatment in step c) is typically a heat treatment, the heat treatment may be caried out by any suitable method, for example using a thermal oven. Such a heat treatment is carried out for a temperature and period of time which reduces the ion-exchange capacity to the desired level, which a skilled person can quantify using the methods disclosed herein. Accordingly, the treatment in step b) is a treatment which is effective to reduce to I2. By way of example, the heat treatment may comprise applying a temperature of greater than about 140°C, suitably greater than about 160°C, for example greater than or equal to about 180°C to the ion-conducting membrane prepared in step b). The temperature is typically less than or equal to about 330°C, suitably less than or equal to about 260°C, typically less than or equal to about 230°C. The heat treatment may be carried out for a period of time in the range of and including about 1 minute to about 20 minutes, suitably about 2 minutes to about 18 minutes, typically about 4 minutes to about 14 minutes. l2 may typically be less than or equal to about 4 meq / g, suitably less than or equal to about 3.5 meq / g, for example less than or equal to about 3 meq / g. I2 may typically be greater than or equal to about 1 meq / g, typically greater than or equal to about 2 meq / g. A titration method can be used to determine the ion-exchange capacity. For example, membranes in the acid form (H+) may be converted to the sodium salt form by immersing the membranes in a 1 .0 M NaCI solution for 24 h to exchange the H+ions with Na+ions. Then, the exchanged H+ions within the solutions may be titrated with a 0.02 N NaOH solution. The theoretical ion-exchange capacity calculated from sulphonated degree may be obtained from the formula: ion-exchange capacity (meq / g) = Ionic mmol concentration / mass of dry membrane at 25 °C.

[0032] The sulphonated hydrocarbon ionomer may suitably comprise a repeating unit of Formula (I): wherein:

[0033] RIA, RIB, RIC, RI D, RIE and RI F are independently aryl or heteroaryl, each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, and SOs'X+, wherein X+is H+or a cation, and provided that at least two of RIA, RIB, R1 C, RID, RIE and RI F are independently aryl or heteroaryl, each optionally substituted with 1 ,2, 3, 4 or 5 SOs'X+substituents;

[0034] RIG and RI H are independently H, aryl, or heteroaryl, wherein said aryl and heteroaryl are each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from Ci- 6 alkyl, halo, nitro, cyano, and SOs'X+, wherein X+is H+or a cation, typically, RIG and RI H are H;

[0035] Ai is arylene, heteroarylene, or heteroalkylene, each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl;

[0036] A2 is absent, arylene, heteroarylene, or heteroalkylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl;

[0037] Li is an optionally substituted linking heteroatom, arylene, heteroarylene, aralkylene, or heteroaralkylene, wherein said arylene, heteroarylene, aralkylene, and heteroaralkylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl; l_2 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl; and

[0038] L3 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from C1-6 alkyl, halo, nitro, cyano, aryl, and heteroaryl.

[0039] RIG and RI H may independently be H.

[0040] The repeating unit of Formula (I) may suitably be a repeating unit of Formula (l-A): wherein:

[0041] RIA, RIB, RIC, RID, RIE and RI F are independently aryl or heteroaryl, each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from C1-6 alkyl, halo, nitro, cyano and SOs'X+, wherein X+is IT or a cation, and provided that at least two of RiA, RIB, R1 C, RID, RIE and RI F are independently aryl or heteroaryl, each optionally substituted with 1 ,2, 3, 4 or 5 SOs'X+substituents;

[0042] R2A, R2B, R2C, R2D are independently H, halo, nitro, cyano, aryl, or heteroaryl;

[0043] Li is an optionally substituted linking heteroatom, arylene, heteroarylene, aralkylene, or heteroaralkylene, wherein said arylene, heteroarylene, aralkylene, and heteroaralkylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl;

[0044] L2 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from C1-6 alkyl, halo, nitro, cyano, aryl, and heteroaryl; and

[0045] L3 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from C1-6 alkyl, halo, nitro, cyano, aryl, and heteroaryl. RIA, RIB, RIC, RID, RIE and RIF may independently be aryl or heteroaryl, each optionally substituted with 1 ,2,3,4 or 5 SOTX+, wherein X+is H+or a cation, and provided that at least two of RiA, RIB, R1 C, RID, RiE and RIF are independently aryl or heteroaryl substituted with 1 ,2, 3, 4 or 5 SOTX+. RIA, RIB, RIC, RID, RIE and RIF may independently be aryl optionally substituted with 1 ,2, 3, 4 or 5 SOTX+, wherein X+is H+or a cation, and provided that at least two of RiA, RIB, R1C, RID, R^ and RIF are independently aryl substituted with 1 ,2, 3, 4 or 5 SOs' X+. RIA, RIB, RIC, RID, RIE and RIF may independently be phenyl optionally substituted with 1 ,2, 3, 4 or 5 SOs'X+, wherein X+is H+or a cation, and provided that at least two of RIA, RIB, R1c, RID, RIE and RIF are independently phenyl substituted with 1 ,2, 3, 4 or 5 SOs'X+.

[0046] X+may be H+or a cation selected from [N(RSA) (RSB) (RSC) (RSD)]+and alkali metal ion, wherein RSA, RSB, RSC, RSD are independently H, Ci-ealkyl, aryl, or heteroaryl.

[0047] Ai may be arylene optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl. A2 may be absent. Alternatively, A2 may be arylene optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl.

[0048] R2A, R2B, R2C, R2D may be independently H or halo. Typically, R2A, R2B, R2C, R2D are each H.

[0049] Li may be arylene or heteroarylene, each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl, halo, aryl, and heteroaryl. Suitably, Li is arylene or heteroarylene, each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. Typically, Li is arylene or heteroarylene, each optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. Typically, Li is arylene or heteroarylene. Suitably, Li is arylene optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. Typically, Li is arylene optionally substituted with 1 , 2, 3, or 4 C1.6 alkyl. Typically, Li is arylene. Li may be naphthalenylene, phenylene, or Ci-e alkylsubstituted phenylene. Suitably, Li is phenylene, or Ci-e alkyl-substituted phenylene.

[0050] L2 may be absent. Alternatively, L2 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. L2 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. L2 may be arylene, or heteroarylene. L2 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. L2 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. L2 may be arylene. L2 may be phenylene.

[0051] L3 may be absent. Alternatively, L3 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. L3 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. L3 may be arylene, or heteroarylene. L3 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. L3 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. L3 may be arylene. L3 may be phenylene.

[0052] Formula (I) may suitably be a repeating unit of Formula (l-B):

[0053] -L3-L2-L1- may be selected from:

[0054]

[0055] The sulphonated hydrocarbon ionomer may suitably also comprise a hydrophobic repeating unit of Formula (II): wherein:

[0056] R3A, R3B, R3C, R3D, R3E and R3F are independently aryl or heteroaryl, each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from Ci-e alkyl, halo, nitro, and cyano; R3G and RSH, are independently H aryl, or heteroaryl, wherein said aryl and heteroaryl are each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from Ci- 6 alkyl, halo, nitro, and cyano, typically RSG and RSH are independently H;

[0057] Bi is arylene, heteroarylene, aralkylene, or heteroalkylene, each optionally substituted with 1 ,2,3 or 4 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl;

[0058] B2 is absent, arylene or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3 or 4 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl;

[0059] Ki is an optionally substituted linking heteroatom, arylene, heteroarylene, aralkylene, or heteroaralkylene, wherein said arylene, heteroarylene, aralkylene, and heteroaralkylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl;

[0060] K2 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from C1-6 alkyl, halo, nitro, cyano, aryl, and heteroaryl; and

[0061] K3 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from C1-6 alkyl, halo, nitro, cyano, aryl, and heteroaryl.

[0062] The repeating unit of Formula (II) may suitably be a repeating unit of Formula (I l-A): wherein;

[0063] RSA, RSB, Rsc, RSD, RSE and RSF are independently aryl or heteroaryl, each optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from C1-6 alkyl, halo, nitro, cyano;

[0064] R4A, R4B, R4C, R4D are independently H, halo, nitro, cyano, aryl, or heteroaryl; Ki is an optionally substituted linking heteroatom, arylene, heteroarylene, aralkylene, or heteroaralkylene, wherein said arylene, heteroarylene, aralkylene, and heteroaralkylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl;

[0065] K2 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl; and

[0066] K3 is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 ,2,3, or 4 substituents independently selected from C1-6 alkyl, halo, nitro, cyano, aryl, and heteroaryl.

[0067] R3A, RSB, Rsc, RSD, RSE and RSF may independently be aryl optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from Ci-ealky and halo. RSA, RSB, RSC, RSD, RSE and RSF may independently be phenyl optionally substituted with 1 ,2, 3, 4 or 5 substituents independently selected from Ci-e alky and halo.

[0068] Bi may optionally be arylene optionally substituted with 1 ,2,3, or 4 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl.

[0069] B2 may be absent. Alternatively, B2 may be arylene optionally substituted with 1 ,2,3, or 4 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl.

[0070] R4A, R4B, R4c, R4D may independently be H or halo. Typically, R4A, R4B, R4C, R4D are each H.

[0071] Ki may be arylene or heteroarylene, each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from C1-6 alkyl, halo, aryl, and heteroaryl. Ki may be arylene or heteroarylene, each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from C1-6 alkyl and halo. Ki may be arylene or heteroarylene, each optionally substituted with 1 , 2, 3, or 4 C1-6 alkyl. Ki may be or heteroarylene. Ki may be arylene optionally substituted with 1 , 2, 3, or 4 substituents independently selected from C1-6 alkyl and halo. Ki may be arylene optionally substituted with 1 , 2, 3, or 4 C1-6 alkyl. Ki may be arylene. K 1 may be naphthalenylene, phenylene, or C1-6 alkyl-substituted phenylene. Ki may be phenylene, or C1-6 alkyl-substituted phenylene.

[0072] K2 may be absent. Alternatively, K2 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. K2 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. K2 may be absent, arylene, or heteroarylene. K2 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. K2 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. K2 may be arylene. K2 may be phenylene.

[0073] K3may be absent. Alternatively, K3 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. K3 may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. K3 may be arylene, or heteroarylene. K3 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 substituents independently selected from Ci-e alkyl and halo. K3 may be arylene, wherein said arylene is optionally substituted with 1 , 2, 3, or 4 Ci-e alkyl. K3 may be arylene. K3 may be phenylene.

[0074] Formula (II) may suitably be a repeating unit of Formula (I l-B):

[0075] -K3-K2-K1- may be selected from:

[0076]

[0077] The sulphonated hydrocarbon ionomer may suitably comprise a first repeating unit of Formula (I) as defined above and a second repeating unit of Formula (II) as defined above, wherein a mole ratio of the first repeating unit to the second repeating unit is in the range of and including about 1 :99 to about 99: 1. The sulphonated hydrocarbon ionomer may be a block copolymer comprising a first block having a repeating unit of Formula (I) as defined above and a second block having a second repeating unit having a Formula (II) as defined above. The number of repeating units of Formula (I) in the first block may be in the range of and including about three to about one hundred, and the number of repeating units having of Formula (II) in the second block may be in the range of and including about three to about one hundred.

[0078] The sulphonated hydrocarbon ionomer may be linear. The sulphonated hydrocarbon ionomer may be branched.

[0079] The sulphonated hydrocarbon ionomer further may further comprise a multivalent linker Mi directly bound via covalent bonds to at least 3 repeating units. Mi may be a trivalent, tetravalent, pentavalent, or hexavalent linker. Suitably Mi is selected from carbon atom, heteroatom (e.g., N, P, or B), multivalent aryl, multivalent heteroaryl, multivalent aralkyl, or multivalent heteroaralkyl, wherein said carbon atom, heteroatom (e.g., P), multivalent aryl, multivalent heteroaryl, multivalent aralkyl, or multivalent heteroaralkyl are each optionally substituted with 1 , 2, or 3 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl. Suitably, Mi may be selected from trivalent nitrogen, tetravalent carbon, trivalent phenyl, trivalent pyridyl, trivalent pyrazyl, tetravalent phenyl, tetravalent pyridyl, tetravalent pyrazyl, pentavalent phenyl, pentavalent pyridyl, and hexavalent phenyl; wherein the trivalent phenyl and trivalent pyridyl are each optionally substituted with 1 , 2, or 3 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl; wherein the tetravalent phenyl, tetravalent pyridyl, and trivalent pyrazyl are each optionally substituted with 1 or 2 substituents independently selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl; and wherein the pentavalent phenyl is optionally substituted with a substituent selected from Ci-e alkyl, halo, nitro, cyano, aryl, and heteroaryl. The multivalent linker Mi may be selected from:

[0080] The sulphonated hydrocarbon ionomer provided in step a) may suitably have a density in dry powder form of at least about 0.9 g / cm3. The sulphonated hydrocarbon ionomer may suitably have a density in dry powder form of less than or equal to about 2 g / cm3, suitably less than or equal to about 1.5 g / cm3.

[0081] The sulphonated hydrocarbon ionomer provided in step a) may have any suitable molecular weight. However, the present process has a particular advantage of providing access to ion-conducting membranes formed from sulphonated hydrocarbon ionomers with a high molecular weight which are generally not readily cast from conventional casting solvents. High molecularweight ionomers can be desirable because of improved mechanical properties. High molecular weight ionomers are generally ionomers having a molecular weight greater than about 25,000 Daltons. Accordingly, it may be suitable for the ionomer provided in step a) to have a molecular weight of greater than about 25,000 Daltons. The molecular weight is the weight average molecular weight as measure using gel permeation chromatography.

[0082] The process may further comprise a step of adding a reinforcing layer, which may comprise a porous polymer material, wherein the sulphonated hydrocarbon ionomer is impregnated within the porous polymer material. The process will therefore provide a reinforced ion-conducting membrane. The reinforcing layer is typically planar. The porous polymer material may be a fluoropolymer. The porous polymer material may be selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethersulphone (PES), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimides (PI), polyetherimide (PEI), poly(aryl ether ketone) (PAEK), poly(aryl ether sulphone), poly(phenylene sulphide) (PPS) and polyvinylpyrrolidone (PVP). The porous polymer material may be expanded polytetrafluoroethylene (ePTFE). The porous polymer material may also comprise a polymer backbone based on a nitrogen-containing heterocycle. The nitrogencontaining heterocycle may comprise basic functional groups. The nitrogen-containing basic functional groups can be nitrogen with a lone pair. The polymer backbone can be suitably derived from polybenzimidazoles, poly(pyridine)s, poly(pyrimidine)s, polybenzthiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polyoxazoles, polybenzoxazoles, polythiazoles, polypyrazoles, and derivatives thereof. Suitably, the polymer backbone is derived from a functionalised polyazole or a zwitterionic polyazole, such as a polybenzimidazole, polytriazole, polythiazole and polydithiazole and their derivatives; most suitably a polybenzimidazole. It will be understood by the skilled person that the polymer backbone may comprises more than one type of nitrogen-containing heterocycle, or a mixture of a nitrogen-containing heterocycles and other aliphatic or aromatic groups.

[0083] Suitably, the reinforcing layer has a maximum thickness of 100 % of the thickness of the reinforced ion-conducting membrane such as a maximum thickness of 90 %, 80 %, 70 %, 60 %, or 50 % of the thickness of the ion-conducting membrane. The porous polymer material suitably has a minimum thickness of 5 % of the thickness of the ion-conducting membrane, such as a minimum thickness of 10 %, 15 %, 20 %, 25 % or 30 % of the thickness of the ionconducting membrane. Suitably, the porous polymer material in the ion-conducting membrane may have a thickness in the range of and including 5 to 95 % of the thickness of the reinforced ion-conducting membrane, such as a thickness in the range of and including 10 to 90 % or 20 to 80 % of the thickness of the reinforced ion-conducting membrane. More than one, for example two, reinforcing layer(s), each having sulphonated hydrocarbon ionomer impregnated in at least a region thereof, may be added in the process. It will be understood that, in the case that the reinforced ion-conducting membrane has more than one reinforcing layer the maximum and / or minimum thickness is the sum of the thickness of each porous polymer structure. The thickness of the or each porous polymer structure, as a proportion of the reinforced ion-conducting membrane may be determined, for example, from a scanning electron microscope (SEM) image of a cross section of the reinforced ionconducting membrane when suitably dried at 0 % relative humidity.

[0084] The thickness of the ion-conducting membrane prepared by the process will depend on its intended use. For example, an ion-conducting membrane for a water electrolyser will typically be thicker than for a fuel cell but that may not always be the case. Suitably, the ionconducting membrane has a thickness as determined by analysis of a scanning electron microscope (SEM) image of a cross section of the membrane when suitably dried at 0 % relative humidity of at least about 5 micrometres. Suitably, the ion-conducting membrane has a thickness of at least about 6 micrometres, about 7 micrometres, about 8 micrometres, about 9 micrometres or at least about 10 micrometres. Typically, the thickness of the ion-conducting membrane when suitably dried at 0% relative humidity is less than or equal to about 200 micrometres, such as less than or equal to about 150 micrometres, less than or equal to about 100 micrometres, less than or equal to about 50 micrometres, less than or equal to about 30 micrometres, less than or equal to about 25 micrometres, or less than or equal to about 20 micrometres. The thickness of the ion-conducting membrane may be determined by analysis of a scanning electron microscope (SEM) image of a cross section of the membrane. Suitably, the ion-conducting membrane has a thickness when suitably dried at 0 % relative humidity in the range of and including about 5 micrometres to about 200 micrometres, about 6 to about 100 micrometres, about 6 to about 50 micrometres, about 7 to about 30 micrometres, or about 8 to about 20 micrometres.

[0085] Step b) comprises casting an ion-conducting membrane from a mixture of the sulphonated hydrocarbon ionomer provided in step a) with a solvent. Suitably, the solvent comprises an alcohol. The alcohol may be linear or branched, typically linear. The solvent may comprise a mixture of two or more, suitably two solvents, for example two different alcohols. One of the solvents may be water. For example, mixtures of alcohol and water may be used because can be high enough for the ionomer provided in step a) to be processable using such mixtures. In the process, the sulphonated hydrocarbon ionomer is first mixed with the solvent. The mixture may be in the form of a dispersion, e.g. a fine suspension of ionomer particles, a solution, or may contain dissolved and dispersed elements i.e. partial dissolution of the ionomer in the solvent. The mixture typically comprises at least about 1 weight percent of the sulphonated hydrocarbon ionomer by total weight of the mixture. The mixture typically comprises no more than about 30 weight percent of the sulphonated hydrocarbon ionomer by total weight of the mixture. Any suitable method of casting may be used including, for example spraying, electro-spraying, screen printing, rotary screen printing, inkjet printing, brush coating, painting, immersion or dipping, bar coating, pad coating, gravure; gap coating techniques such as knife or doctor blade over roll (whereby the coating is applied to the substrate then passes through a split between the knife and a support roller); slot die (slot, extrusion) coating (whereby the coating is squeezed out by gravity or under pressure via a slot onto the substrate); metering rod application such as with a Meyer bar and gravure coating. Suitably, the casting method is selected from gravure, slot die coating and inkjet printing. Following casting, a drying step is typically carried out to form the ion-conducting membrane for example at a temperature in the range of and including about 50°C to about 150°C. Drying may be carried out, for example for a time of less than about 15 minutes, typically less than about 10 minutes.

[0086] Also provided is a process for preparing a catalyst-coated membrane for a fuel cell or a water electrolyser, the catalyst-coated membrane comprising a catalyst layer on a face of an ion-conducting membrane. The ion-conducting membrane is prepared by a process as defined herein. The catalyst layer(s) is / are prepared by forming an ink comprising the required constituents of the catalyst layer in a mixture with a solvent. The catalyst layer(s) is / are cast by any suitable technique, including those described above in connection with casting of the ion-conducting membrane. The process of the disclosure is particularly suitable for so called additive layer-type processes for preparing catalyst-coated membranes in which the catalyst- coated membrane is built up layer by layer. It is also particularly suitable for direct-to- membrane printing of catalyst layers i.e. processes in which the catalyst layer is cast directly on to the ion-conducting membrane. This is because, for example, when a catalyst layer is cast on the ion-conducting membrane it can be dissolved by the solvent used for the catalyst layer ink. However, when an ionomer having an ion-exchange capacity is used to cast the membrane and that ion-exchange capacity is subsequently reduced to I2, the membrane having the ion-exchange capacity I2 may no longer be soluble in the solvent used for the catalyst layer ink.

[0087] The catalyst layer comprises one or more electrocatalysts. The one or more electrocatalysts may be independently a finely divided unsupported metal powder, or a supported catalyst wherein small nanoparticles are dispersed on electrically conducting particulate carbon supports. The electrocatalyst metal is suitably selected from: (i) the platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium),

[0088] (ii) gold or silver,

[0089] (iii) a base metal, or an alloy or mixture comprising one or more of these metals or their oxides.

[0090] A suitable electrocatalyst metal is platinum, which may be alloyed with other precious metals or base metals. A base metal is tin or a transition metal which is not a noble metal. A noble metal is a platinum group metal (platinum, palladium, rhodium, ruthenium, iridium or osmium), gold or silver. Suitable base metals include copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium and tin. Suitable base metals are nickel, copper, cobalt, and chromium. More suitable base metals are nickel, cobalt and copper. If the electrocatalyst is a supported catalyst, the loading of metal particles on the carbon support material is suitably in the range 10-90 wt%, typically 15-75 wt% of the weight of resulting electrocatalyst. The exact electrocatalyst used will depend on the reaction it is intended to catalyse and its selection is within the capability of the skilled person.

[0091] The catalyst layer will typically comprise an ionomer which may be a perfluorosulphonic acid ionomer. Alternatively, the ionomer may be a sulphonated hydrocarbon ionomer as defined herein. The catalyst layer may further comprise additional components. Such additional components include, but are not limited to, a catalyst which facilitates oxygen evolution and therefore will be of benefit in cell reversal situations and high potential excursions, or a hydrogen peroxide decomposition catalyst. Examples of such catalysts and any other additives suitable for inclusion in the catalyst layer will be known to those skilled in the art.

[0092] Also provided is a process for preparing a membrane electrode assembly comprising a catalyst-coated ion-conducting membrane and a gas diffusion layer or porous transport layer present on the at least one of the catalyst layers. The anode and cathode gas diffusion layers are suitably based on conventional gas diffusion substrates. Typical substrates include nonwoven papers or webs comprising a network of carbon fibres and a thermoset resin binder (e.g. the TGP-H series of carbon fibre paper available from Toray Industries Inc., Japan or the H2315 series available from Freudenberg FCCT KG, Germany, or the Sigracet® series available from SGL Technologies GmbH, Germany or AvCarb® series from Ballard Power Systems Inc.), or woven carbon cloths. The carbon paper, web or cloth may be provided with a further treatment prior to being incorporated into a MEA either to make it more wettable (hydrophilic) or more wet-proofed (hydrophobic). The nature of any treatments will depend on the type of fuel cell and the operating conditions that will be used. The substrate can be made more wettable by incorporation of materials such as amorphous carbon blacks via impregnation from liquid suspensions, or can be made more hydrophobic by impregnating the pore structure of the substrate with a colloidal suspension of a polymer such as PTFE or polyfluoroethylenepropylene (FEP), followed by drying and heating above the melting point of the polymer. For applications such as the PEMFC, a microporous layer may also be applied to the gas diffusion substrate on the face that will contact the catalyst layer. The microporous layer typically comprises a mixture of a carbon black and a polymer such as polytetrafluoroethylene (PTFE). The porous transport layer is suitably based on conventional porous transport substrates, such as a titanium mesh.

[0093] Examples

[0094] Ionomer mixture synthesis

[0095] The following mixtures were prepared of a sulphonated phenylated polyphenylene ionomer having a repeating unit of Formula l-B and a hydrophobic repeating unit, an ion-exchange capacity (I EC) in the range of 2.8 to 3.1 meq / g and a density of about 1.2 g / cm3in a mixture of iso-propyl alcohol (I PA) and water.

[0096] Mass and dimension change testing

[0097] Ion-conducting membranes comprising a sulphonated phenylated polyphenylene ionomer having a repeating unit of Formula l-B and a hydrophobic repeating unit, an I EC in the range of 2.8 to 3.1 meq / g and a density of 1.2 g / cm3were subjected to a heat treatment in a thermal oven. Two membranes were placed in at 140°C, one left for 5 minutes (Example 1) the other for 10 minutes (Example 2). Two membranes were placed in at 180°C, one left for 5 minutes (Example 3) the other for 10 minutes (Example 4). A standard blank was left aside, giving five membranes in total.

[0098] The heat-treated membranes are then subjected to a swell test. The membranes dimensions and mass are measured (ambient state), before submerging the membranes in 80°C water back for 24 hours (wet state). Over this time the membranes swell. After 24h they are removed before mass and dimensions are measured again.

[0099] Fig. 2 shows the percentage mass change for the blank and Examples 1 to 4. This reduction in mass change, particularly after treatments at 180°C, provides membranes with more favourable water uptake which can be attributed to lower I EC. An ideal membrane (from a mechanical perspective) should display the lowest water uptakes and the least dimension change (resistance to deformation). The higher temperature, longer heat treatments lead to lower water uptakes (comparing the dried to the wet state) with a clear trend of increasing water uptake with less heat treatment (see attached documents).

[0100] A similar trend is seen in Fig. 4 with the in-plane (x) dimension percentage change.

[0101] Further experiments were also conducted on ion-conducting membranes comprising a sulphonated phenylated polyphenylene ionomer having a repeating unit of Formula l-B and a hydrophobic repeating unit, an I EC in the range of 3.1 to 3.4 meq / g and a density of about 1.2 g / cm3. In these experiments membranes were subjected to heat treatments in a thermal oven as set out in Table 2.

[0102] Table 2

[0103] Fig. 3 shows the mass change for Examples 5 to 10 when subjected to the same swell test conditions. The reduction in mass change is again seen particularly after treatments greater than 160°C, to provide membranes with more favourable water uptake which can be attributed to lower I EC.

[0104] A similar trend can be seen in Fig. 5 with the in-plane (x) dimension percentage change. Fig. 6 correlates the data shown in Figs. 3 and 5 in terms of percentage mass change and percentage change in the in-plane (x) dimension and demonstrates the favourable properties particularly after heat treatment at temperatures of greater than or equal to 180°C.

[0105] Ion-exchange capacity measurements

[0106] I EC of the membranes was measure using a conventional titration technique. The membranes in the acid form (H+) are converted to the sodium salt form by immersing the membranes in a 1.0 M NaCI solution for 24 h to exchange the H+ions with Na+ions. Then, the exchanged H+ions within the solutions may be titrated with a 0.02 N NaOH solution. The theoretical ionexchange capacity calculated from sulphonated degree is obtained from the formula: ionexchange capacity (meq / g) = Ionic mmol concentration / mass of dry membrane at 25 °C.

[0107] Fig. 7 shows the I EC of Examples 5 to 10, with a loss of I EC due loss of sulphonate groups evident which is increased with an increase in heat treatment temperature.

[0108] Fig. 8 provides a correlation between IEC after heat treatment and percent mass change from dry to wet membrane determined using the procedure mentioned above. The beneficial reduction in dry to wet mass change after heat treatment correlates with loss of IEC.

[0109] Thermogravimetric analysis

[0110] Thermogravimetric analysis was carried out on Samples 1 to 5. Samples are loaded into TGA / DSC pans and placed into a SDT 650 DSC / TGA system. The samples are held at 30°C for 20 minutes before ramping to 600°C at 10°C / min. The change in heat flow and mass are measured as a function of temperature.

[0111] The data is shown in Figs. 9 and 10. It can be seen from these figures that there is a first mass loss between 80 and 100°C. This can be associated with water loss. There is a second mass loss between 150°C and 250°C. This is associated with loss in sulphonate as seen in the literature: “Highly Stable, Low Gas Crossover, Proton-Conducting Phenylated Polyphenylenes", Angew. Chem. Int. Ed., 56, 2017 pp 9058-9061 , and it follows loss in IEC. As shown in Fig. 5, there is no significant difference in thermal transitions when the amount of alcohol solvent is increased with respect to water.

[0112] FTIR measurements

[0113] FTIR data was acquired from Examples 5 to 10 using an ATR FTIR instrument. Spectra are collected at room temperature using a crystal diamond plate. The plate is left empty for a background spectrum, with subsequently collected membranes spectra being corrected by subtracting the background spectra.

[0114] The spectra are provided in Fig. 1. This data shows a change in chemical structure for heat treatments greater than 180°C. Specifically, the loss of the peaks around 1000 - 1050cm-1are associated with the loss of sulphonic acid, with a clear decrease in peak area (100°C = 140°C = 160°C > 180°C » 200°C » 220°C).

Claims

Claims:

1. A process of preparing an ion-conducting membrane comprising a sulphonated hydrocarbon ionomer having an ion-exchange capacity I2 meq / g, the process comprising the steps of: a) providing a sulphonated hydrocarbon ionomer having an ion-exchange capacity meq / g;b) casting an ion-conducting membrane from a mixture of the sulphonated hydrocarbon ionomer provided in step a) and a solvent; c) applying a treatment to the ion-conducting membrane prepared in step b) which reduces the ion-exchange capacity from meq / g to an ion-exchange capacity I2 meq / g, wherein I2 is less than .

2. A process according to claim 1 , wherein the treatment applied in step c) is a heat treatment.

3. A process according to any preceding claim, wherein is greater than or equal to about 5 meq / g.

4. A process according to any preceding claim, wherein I2 is less than or equal to about 4 meq / g.

5. A process according to any preceding claim, wherein the sulphonated hydrocarbon ionomer provided in step a) has a molecular weight of greater than about 25,000 Daltons.

6. A process according to any preceding claim, wherein the solvent used in step b) comprises an alcohol.

7. A process according to any preceding claim, wherein the sulphonated hydrocarbon ionomer is selected from sulphonated derivatives of poly(arylene ether)s, poly(arylene ether ketone)s, poly(arylene sulphone)s, poly(imide)s, poly(benzimidazole)s, polyphenylenes and phenylated polyphenylenes.

8. A process according to any preceding claim, further comprising a step of adding a reinforcing layer.

9. A process of preparing a catalyst-coated membrane for a fuel cell or a water electrolyser, the catalyst-coated membrane comprising a catalyst layer on a face of an ionconducting membrane, the process comprising: i) preparing an ion-conducting membrane by a process as defined in any of claims 1 to 8; ii) preparing a catalyst layer; wherein either the catalyst layer is prepared and the ion-conducting membrane is applied to the catalyst layer, or the ion-conducting membrane is prepared and the catalyst layer is applied to the ion-conducting membrane.

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