Hydrocarbon membrane

Abstract

The disclosure provides an ion-conducting membrane, the ion-conducting membrane comprising a sulphonated hydrocarbon ionomer, wherein the ion-conducting membrane has a Lambda value of less than about 60.

Description

[0001] Hydrocarbon membrane Field of the Invention This invention relates to ion-conducting membranes containing sulphonated ionomers, which demonstrate reduced water uptake. In particular, this invention relates to proton exchange membranes, and processes of manufacturing the same. The ion-conducting membranes can be suitable for use in electrochemical devices such as fuel cells and / or electrolysers. Background of the Invention 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. 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. 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). 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. 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. For example, current membranes containing hydrocarbon ionomers swell excessively without mechanical support and are unable to effectively regulate the water within the membrane during operation. It is desirable to provide membranes made from hydrocarbon ionomers which address these issues. Summary of the Invention Accordingly, the disclosure provides an ion-conducting membrane, the ion-conducting membrane comprising a sulphonated hydrocarbon ionomer, wherein the ion-conducting membrane has a Lambda value of less than about 60. The ion-conducting membrane is accordingly a hydrocarbon membrane, i.e. it does not comprise fluorinated ionomer. As set out herein, Lambda is a measure of water uptake and in the present case is determined after water uptake at about 80°C, which is representative of temperatures faced during real-word use, for example of a proton exchange membrane fuel cell, for example in an automotive application. The values are surprisingly and advantageously low. In prior art disclosures in which Lambda is measured after water uptake at ambient temperatures such as 22°C, Lambda is of course lower at such temperatures because water uptake is not as facile at lower temperatures. However, such a temperature is not representative of the temperatures faced during real world use of a membrane. Suitably the ion-conducting membrane has a wet membrane average domain spacing (Å) as determined by small-angle X-ray scattering (SAXS) of less than or equal to about 37, suitably the ion-conducting membrane has a wet membrane correlation length (Å) as determined by SAXS of less than or equal to about 9. Accordingly, the inventors have surprisingly found ion-conducting membranes made from sulphonated hydrocarbon ionomers which take up less water and have greater dimensional stability, mitigating swelling. These are fundamental effects for providing ion-conducting membranes comprising sulphonated hydrocarbon ionomers which can operate effectively in a fuel cell or water electrolyser. The disclosure also provides a process of preparing an ion-conducting membrane according to the disclosure, the process comprising casting the membrane from a mixture of the sulphonated hydrocarbon ionomer and a solvent. It has surprisingly been found by the present inventors that ion-conducting membranes comprising a sulphonated hydrocarbon ionomer having the advantageous properties discussed above can be cast at ambient temperature, and the properties can be controlled by the identity of the solvent. The disclosure also provides a catalyst-coated membrane for a fuel cell or a water electrolyser comprising an ion-conducting membrane according to the disclosure, with a cathode catalyst layer applied to a first face of the membrane and / or an anode catalyst layer applied to a second face of the membrane. The catalyst layer may comprise a perfluorosulphonic acid ionomer or a hydrocarbon ionomer. The disclosure also provides a membrane-electrode assembly for a fuel cell or a water electrolyser comprising (i) an ion-conducting membrane according to the disclosure; or (ii) a catalyst-coated membrane according to the disclosure; and at least one of a gas diffusion layer or a porous transport layer. The disclosure also provides a water electrolyser or a fuel cell comprising a catalyst- coated membrane according to the disclosure or a membrane-electrode assembly according to the disclosure. Brief Description of the Drawings Figure 1 is a chart showing the percent change in mass between dried and wet states of membranes comprising a sulphonated hydrocarbon ionomer against the length of the alcohol chain that the membrane was cast from. Figure 2 is a chart showing normalised values for the mass change between different states when compared to the ambient state of membranes comprising a sulphonated hydrocarbon ionomer cast from alcohols having different chain lengths. Figure 3 is a chart showing the Lambda value for ion-conducting membranes comprising a sulphonated hydrocarbon ionomer cast from alcohols having different chain lengths. Figure 4 is a chart showing swelling in the transverse, in plane, direction of ion- conducting membranes comprising a sulphonated hydrocarbon ionomer cast from alcohols having different chain lengths. Figure 5 is a chart showing swelling in the through-plane direction of ion-conducing membranes comprising a sulphonated hydrocarbon ionomer cast from alcohols having different chain lengths. Figure 6 is a chart showing the correlation length and domain spacing as determined by short-angle X-ray scattering (SAXS) for ion-conducting membranes comprising a sulphonated hydrocarbon ionomer cast from alcohols having different chain lengths. Figure 7 is a chart showing the trends of Lambda value and casting alcohol chain length against both correlation length and domain spacing as determined by SAXS for ion- conducting membranes comprising a sulphonated hydrocarbon ionomer. Detailed Description 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 PemionTMrange of sulphonated hydrocarbon ionomers from Ionomr Innovations. The sulphonated phenylated polyphenylene hydrocarbon ionomer may be linear or branched. 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. 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 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. The molar ratio of the repeating unit comprising a sulphonated moiety and the hydrophobic repeating unit may suitably be in the range of and including about 1:99 to about 99:1, suitably about 1:50 to about 50:1, more suitably about 1:25 to about 25:1, typically about 1:10 to about 10:1, for example about 1:2.5 to about 2.5:1. 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. The sulphonated hydrocarbon ionomer may suitably comprise a repeating unit of Formula (I): wherein: R1A, R1B, R1C, R1D, R1Eand R1Fare independently aryl or heteroaryl, each optionally substituted with 1,2,3,4 or 5 substituents independently selected from C1-6alkyl, halo, nitro, cyano, and SO3-X+, wherein X+is H+or a cation, and provided that at least two of R1A, R1B, R1C, R1D, R1Eand R1Fare independently aryl or heteroaryl, each optionally substituted with 1,2,3,4 or 5 SO3-X+substituents; R1Gand R1Hare 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 C1-6alkyl, halo, nitro, cyano, and SO3-X+, wherein X+is H+or a cation, typically, R1Gand R1Hare H; A1is arylene, heteroarylene, or heteroalkylene, each optionally substituted with 1,2,3,4 or 5 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl; A2is 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; L1is 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 C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; L2is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; and L3is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl. R1Gand R1Hmay independently be H. The repeating unit of Formula (I) may suitably be a repeating unit of Formula (I-A): wherein: R1A, R1B, R1C, R1D, R1Eand R1Fare independently aryl or heteroaryl, each optionally substituted with 1,2,3,4 or 5 substituents independently selected from C1-6alkyl, halo, nitro, cyano and SO3-X+, wherein X+is H+or a cation, and provided that at least two of R1A, R1B, R1C, R1D, R1Eand R1Fare independently aryl or heteroaryl, each optionally substituted with 1,2,3,4 or 5 SO3-X+substituents; R2A, R2B, R2C, R2Dare independently H, halo, nitro, cyano, aryl, or heteroaryl; L1is 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 C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; L2is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; and L3is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl. R1A, R1B, R1C,R1D, R1Eand R1Fmay independently be aryl or heteroaryl, each optionally substituted with 1,2,3,4 or 5 SO3-X+, wherein X+is H+or a cation, and provided that at least two of R1A, R1B, R1C,R1D, R1Eand R1Fare independently aryl or heteroaryl substituted with 1,2,3,4 or 5 SO3-X+. R1A, R1B, R1C,R1D, R1Eand R1Fmay independently be aryl optionally substituted with 1,2,3,4 or 5 SO3-X+, wherein X+is H+or a cation, and provided that at least two of R1A, R1B, R1C,R1D, R1Eand R1Fare independently aryl substituted with 1,2,3,4 or 5 SO3- X+. R1A, R1B, R1C,R1D, R1Eand R1Fmay independently be phenyl optionally substituted with 1,2,3,4 or 5 SO3-X+, wherein X+is H+or a cation, and provided that at least two of R1A, R1B, R1C, R1D, R1E and R1F are independently phenyl substituted with 1,2,3,4 or 5 SO3-X+. X+may be H+or a cation selected from [N(R5A) (R5B) (R5C) (R5D)]+and alkali metal ion, wherein R5A, R5B, R5C, R5Dare independently H, C1-6alkyl, aryl, or heteroaryl. A1may be arylene optionally substituted with 1,2,3,4 or 5 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl. A2may be absent. Alternatively, A2may be arylene optionally substituted with 1,2,3,4 or 5 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl. R2A, R2B, R2C,R2Dmay be independently H or halo. Typically, R2A, R2B, R2C,R2Dare each H. L1may be arylene or heteroarylene, each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl, halo, aryl, and heteroaryl. Suitably, L1is arylene or heteroarylene, each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. Typically, L1is arylene or heteroarylene, each optionally substituted with 1, 2, 3, or 4 C1-6alkyl. Typically, L1is arylene or heteroarylene. Suitably, L1is arylene optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. Typically, L1is arylene optionally substituted with 1, 2, 3, or 4 C1-6alkyl. Typically, L1is arylene. L1may be naphthalenylene, phenylene, or C1-6alkyl- substituted phenylene. Suitably, L1is phenylene, or C1-6alkyl-substituted phenylene. L2may be absent. Alternatively, L2may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. L2may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 C1-6alkyl. L2may be arylene, or heteroarylene. L2may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. L2may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 C1-6alkyl. L2may be arylene. L2may be phenylene. L3may be absent. Alternatively, L3may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. L3may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 C1-6alkyl. L3may be arylene, or heteroarylene. L3may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. L3 may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 C1-6alkyl. L3may be arylene. L3may be phenylene. Formula (I) may be a repeating unit of Formula (I-B): . The sulphonated hydrocarbon ionomer may also comprise a hydrophobic repeating unit of Formula (II): wherein: R3A, R3B, R3C, R3D, R3Eand R3Fare independently aryl or heteroaryl, each optionally substituted with 1,2,3,4 or 5 substituents independently selected from C1-6alkyl, halo, nitro, and cyano; R3Gand R3H, 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 C1-6alkyl, halo, nitro, and cyano, typically R3Gand R3Hare independently H; B1is arylene, heteroarylene, aralkylene, or heteroalkylene, each optionally substituted with 1,2,3 or 4 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl; B2is 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; K1is 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 C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; K2is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; and K3is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl. The repeating unit of Formula (II) may suitably be a repeating unit of Formula (II-A): wherein; R3A, R3B, R3C,R3D, R3Eand R3Fare independently aryl or heteroaryl, each optionally substituted with 1,2,3,4 or 5 substituents independently selected from C1-6alkyl, halo, nitro, cyano; R4A, R4B, R4C, R4Dare independently H, halo, nitro, cyano, aryl, or heteroaryl; K1is 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 C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; K2is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; and K3is absent, arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1,2,3, or 4 substituents independently selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl. R3A, R3B, R3C,R3D, R3Eand R3Fmay independently be aryl optionally substituted with 1,2,3,4 or 5 substituents independently selected from C1-6alky and halo.R3A, R3B, R3C,R3D, R3E and R3Fmay independently be phenyl optionally substituted with 1,2,3,4 or 5 substituents independently selected from C1-6alky and halo. B1may optionally be arylene optionally substituted with 1,2,3, or 4 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl. B2may be absent. Alternatively, B2may be arylene optionally substituted with 1,2,3, or 4 substituents independently selected from halo, nitro, cyano, aryl, and heteroaryl. R4A, R4B, R4C,R4Dmay independently be H or halo. Typically, R4A, R4B, R4C,R4Dare each H. K1may be arylene or heteroarylene, each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl, halo, aryl, and heteroaryl. K1may be arylene or heteroarylene, each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. K1may be arylene or heteroarylene, each optionally substituted with 1, 2, 3, or 4 C1-6alkyl. K1may be or heteroarylene. K1may be arylene optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. K1may be arylene optionally substituted with 1, 2, 3, or 4 C1-6alkyl. K1may be arylene. K1may be naphthalenylene, phenylene, or C1-6alkyl-substituted phenylene. K1may be phenylene, or C1-6alkyl-substituted phenylene. K2may be absent. Alternatively, K2may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. K2may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 C1-6alkyl. K2may be absent, arylene, or heteroarylene. K2may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. K2may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 C1-6alkyl. K2may be arylene. K2may be phenylene. K3may be absent. Alternatively, K3may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. K3may be arylene, or heteroarylene, wherein said arylene and heteroarylene are each optionally substituted with 1, 2, 3, or 4 C1-6alkyl. K3may be arylene, or heteroarylene. K3may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 substituents independently selected from C1-6alkyl and halo. K3 may be arylene, wherein said arylene is optionally substituted with 1, 2, 3, or 4 C1-6alkyl. K3may be arylene. K3may be phenylene. Formula (II) may suitably be a repeating unit of Formula (II-B): 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 1:99 to 99:1 suitably about 1:50 to about 50:1, more suitably about 1:25 to about 25:1, typically about 1:10 to about 10:1, for example about 1:2.5 to about 2.5:1. The sulphonated hydrocarbon ionomer is 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. The sulphonated hydrocarbon ionomer may be linear. The sulphonated hydrocarbon ionomer may be branched. The sulphonated hydrocarbon ionomer further may further comprise a multivalent linker M1 directly bound via covalent bonds to at least 3 repeating units. M1 may be a trivalent, tetravalent, pentavalent, or hexavalent linker. Suitably M1 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 C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl. Suitably M1 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 C1-6alkyl, 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 C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl; and wherein the pentavalent phenyl is optionally substituted with a substituent selected from C1-6alkyl, halo, nitro, cyano, aryl, and heteroaryl. The multivalent linker M1 may be selected from:

[0002] The sulphonated hydrocarbon ionomer may suitably have an ion-exchange capacity of less than or equal to about 5 meq / g, suitably 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. The sulphonated hydrocarbon ionomer may suitably have an ion-exchange capacity of 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 NaCl 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. The sulphonated hydrocarbon ionomer may suitably have a molecular weight of less than or equal to about 25,000 Daltons, for example less than or equal to about 20,000 Daltons. The sulphonated hydrocarbon ionomer will typically have a molecular weight of at least about 10,000 Daltons, for example at least about 15,000 Daltons. The molecular weight is the weight average molecular weight as measured using gel permeation chromatography. The sulphonated hydrocarbon ionomer may suitably have a density in dry powder form of at least about 1 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.The ion-conducting membrane has a Lambda value of less than about 60, suitably less than about 50, more suitably less than about 45, more suitably less than about 35, for example less than about 30. Lambda this is a measure of water uptake and in the present case is determined after water uptake at about 80°C, which is representative of temperatures faced during real-word use, for example of a proton exchange membrane fuel cell, for example in an automotive application. Specifically, Lambda is the number of moles of molecules of water per sulphonate group in the ionomer and may be measured by measuring the dried membrane mass (dried in a vacuum membrane at 100°C) and the hydrated membrane mass immediately after being submerged in water for 24h at 80°C, called mwaterand mdried membrane. The following equation can then be used. To correct for membranes with reinforcement the original Lambda equation should be multiplied by the reciprocal of the volume fraction of ionomer, which is found by dividing the volume of dried ionomer by the volume of dried membrane. Volume of dried ionomer can be found by subtracting the volume of reinforcement put in the membrane from the volume of membrane measured. The ion-conducting membrane may suitably have a wet membrane average domain spacing (Å) as determined by small-angle X-ray scattering (SAXS) of less than or equal to about 39, suitably less than or equal to about 37, more suitably less than or equal to about 34, for example less than or equal to about 32. The ion-conducting membrane may suitably have a wet membrane average domain spacing (Å) as determined by SAXS of at least about 20. The ion-conducting membrane may suitably have a wet membrane correlation length (Å) as determined by SAXS of less than or equal to about 9, typically less than or equal to about 7, for example less than or equal to about 8. The ion-conducting membrane may suitably have a wet membrane correlation length (Å) as determined by SAXS of at least about 1. SAXS data is collected using an X-ray source, with a detector to sample distance capable for viewing the q range between 0.01 and 1 Å-1. Background subtractions, for air, capillaries and / or solvents should be completed before model fitting. A Teubner-Strey model is fitted to this region, ensuring a suitable good fit (rejecting chi2values greater than 10). The model provides a correlation length and a domain spacing. These are used to define the polymeric structure in dispersion, solution, or membrane. Herein “wet membrane” refers to membranes submerged in 20°C deionised water for at least 48 hours with membranes sufficiently thick to provide sufficient scattering for background subtraction. Any dispersion / solution SAXS was completed with enough ionomer solids to provide sufficient scattering. The ion-conducting membrane may further comprise a reinforcing layer comprising a porous polymer material, wherein the sulphonated hydrocarbon ionomer is impregnated within the porous polymer material. 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 nitrogen- containing 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. 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 ion- conducting 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. The ion-conducting membrane may suitably contain more than one, for example two, reinforcing layer(s) each having sulphonated hydrocarbon ionomer impregnated in at least a region thereof. 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 ion-conducting membrane when suitably dried at 0 % relative humidity. The thickness of the ion-conducting membrane 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 ion-conducting 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. 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. Disclosed herein is a process of preparing an ion-conducting membrane comprising a sulphonated hydrocarbon ionomer, the process comprising casting the membrane from a mixture of the sulphonated hydrocarbon ionomer and a solvent. The ion-conducting membrane is suitably an ion-conducting membrane as defined herein. 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. Suitably and advantageously, the membrane is cast from the solvent at ambient temperature i.e. the step of casting does not require the application of heat. For example, the casting temperature may be less than about 30°C. The casting temperature may be at least about 15°C, for example at least about 20°C. The step of casting may typically be carried out for a time of less than or equal to about 30 minutes, suitably less than or equal to about 15 minutes, more suitably less than or equal to about 10 minutes, for example less than or equal to about 5 minutes. The solvent may suitably comprise any solvent which forms a membrane having a correlation length (Å) as defined herein at ambient temperature, which a skilled person can determine using the method set out herein. In particular, the mixture itself may suitably have a correlation length (Å) as determined by SAXS of less than or equal to about 9, typically less than or equal to about 7, for example less than or equal to about 8. The mixture may suitably have a correlation length (Å) as determined by SAXS of at least about 1. The solvent may comprise an alcohol, typically an alcohol which comprises 3 or more carbons. Suitably, the alcohol comprises no more than 9 atoms, more suitably no more than 8 atoms, typically no more than 7 carbons. The alcohol may be linear or branched, typically linear. For example, the alcohol may be n-hexanol. Mixtures of such solvents may be used. For example, the main solvent, which has the properties defined above and will form a membrane with the required SAXS correlation length (which can be tested using the procedures disclosed herein) at ambient temperature, may be mixed with one or more additional solvents, typically one to form a binary system, for example with a volume ratio of main solvent to the one or more additional solvents in the range of and including about 0.2:1 or greater, suitably about 0.5:1 or greater, typically about 1:1 or greater. Surprisingly and advantageously, such a mixture may provide ion-conducting membranes with the beneficial properties disclosed herein, but the one or more additional solvent(s) may be selected such that it / they volatilise(s) more quickly and so reduces the time required for casting, which is beneficial. Accordingly, the one or more additional solvent(s) will have a relative evaporation rate higher than the main solvent. Examples of suitable additional solvents include methanol, ethanol and propanol. In the process, the sulphonated hydrocarbon ionomer is first mixed with the solvent. The mixture typically comprises at least about 1 percent by weight of the sulphonated hydrocarbon ionomer by total weight of the mixture. The mixture typically comprises no more than about 30 percent by weight of the sulphonated hydrocarbon ionomer by total weight of the mixture. The mixture may suitably have a wet membrane average domain spacing (Å) as determined by small- angle X-ray scattering (SAXS) of less than or equal to about 39, suitably less than or equal to about 37, more suitably less than or equal to about 34, for example less than or equal to about 32.The mixture may suitably have a wet membrane average domain spacing (Å) as determined by SAXS of at least about 20. 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. 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. Also provided is a catalyst-coated membrane comprising an ion-conducting membrane of the disclosure, with a cathode catalyst layer applied to a first face of the membrane and / or an anode catalyst layer applied to a second face of the membrane. 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), (ii) gold or silver, (iii) a base metal, or an alloy or mixture comprising one or more of these metals or their oxides. Typically, the 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. 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. Also provided is a membrane electrode assembly comprising an ion-conducting membrane of the disclosure and a gas diffusion electrode and / or a porous transport layer on a first and / or second face of the ion-conducting membrane. Also provided is 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 non-woven 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 membrane electrode assembly 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. Also provided is an electrochemical device comprising an ion-conducting membrane, a catalyst-coated membrane, or a membrane-electrode assembly of the disclosure. The electrochemical device can be a fuel cell, such as a proton exchange membrane fuel cell. The electrochemical device can be an electrolyser, such as a water electrolyser. Examples Membrane synthesis A sulphonated phenylated polyphenylene ionomer having a repeating unit of Formula I-B and a hydrophobic repeating unit, an ion-exchange capacity (IEC) in the range of 2.8 to 3.1 meq / g and a density of 1.2 g / cm3is dispersed in a vial of n-alcohol. The n-alcohols; MeOH, EtOH, nPrOH, nBuOH, and nHexOH all can disperse the polyphenylene ionomer, dispersing up to 12.33 wt% material after at least 24h on a room temperature roller bed at 60RPM. The ionomer solvent mixture is cast on a bench-top film coater, using a Baker coater with a 200 micrometre set gap. The hydrocarbon membrane is cast creating a 200 micrometre wet membrane, which is subsequently air dried at 20°C to approximately 13 (+-2) micrometre dry hydrocarbon membrane. Once air dried the membrane is placed in a 100°C thermal oven for 5 minutes to remove any residue solvent. At this stage the membrane can be cut and removed from the backing. Example 1 = cast from MeOH Example 2 = cast from EtOH Example 3 = cast from nPrOH Example 4 = cast from nBuOH Example 5 = cast from nHexOH Example 6 = cast from 1:1 by volume MeOH:nPrOH Example 7 = cast from 1:1 by volume MeOH: nBuOH Mass and dimension change testing The cut 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. The wet membranes are placed inside a vacuum oven, 100°C, for 24 hours (dry state). After drying again the new mass and dimensions are measured. During this test, an ideal membrane would display the lowest mass and dimension change between dry and wet states, whilst maintaining the similar mass and dimensions between ambient and dry states. Fig.1 shows that the mass change between dried and wet states drops with increased chain length of the casting alcohol, with Example 5 showing particularly favourable characteristics. Fig.2 further demonstrates this trend and also shows that the membranes have similar mass between ambient and dry states, which is favourable. Fig.4 shows that swelling reduces in the transverse, in-plane, dimension during the wet state with increased chain length of the casting alcohol, with Example 5 showing particularly favourable characteristics where the long alcohol cast membranes do not excessively thin during the wet cycle, increasing the durability of these membranes. Lambda calculation Lambda is the number of moles of molecules of water per sulphonate group in the ionomer and is measured by measuring the dried membrane mass (dried in a vacuum membrane at 100°C) and the hydrated membrane mass immediately after being submerged in water for 24h at 80°C, called mwater and mdried membrane. The following equation can then be used. Fig. 3 shows that Lambda drops with increased chain length of the casting solvent, with Example 5 showing a value which is particularly surprising and providing a membrane which may effectively regulate water during operation and thus produce a membrane of surprising durability. Moreover, Fig.3 shows that mixtures of solvents, such as used in Examples 6 and 7, can produce membranes in which the water uptake characteristics are controlled by the solvent which provides the most favourable Lambda. Thus, mixtures of solvents can be used in which one solvent is chosen to provide optimal Lambda, and the second solvent is chosen to be more volatile and improve casting time. Small-Angle X-ray Scattering (SAXS) measurements SAXS data is collected using an X-ray source, with a detector to sample distance capable for viewing the q range between 0.01 and 1 Å-1. Background subtractions, for air, capillaries and / or solvents should be completed before model fitting. A Teubner-Strey model is fitted to this region, ensuring a suitable good fit (rejecting chi2values greater than 10). The model provides a correlation length and a domain spacing. These are used to define the polymeric structure in dispersion, solution, or membrane. Herein “wet membrane” refers to membranes submerged in 20°C deionised water for at least 48 hours with membranes sufficiently thick to provide sufficient scattering for background subtraction. Any dispersion / solution SAXS was completed with enough ionomer solids to provide sufficient scattering. Fig. 6 shows that both wet membrane average domain spacing (Å) (d) and wet membrane correlation length (Å) (xi) decrease with increased chain length of the casting alcohol and in turn lower wet membrane average domain spacing (Å) and wet membrane correlation length (Å) correlate with reduced Lambda. Example 5 shows particularly favourable characteristics. All of these correlations are illustrated in Fig.7.

Claims

Claims:

1. An ion-conducting membrane, the ion-conducting membrane comprising a sulphonated hydrocarbon ionomer, wherein the ion-conducting membrane has a Lambda value of less than about 60.

2. An ion-conducting membrane according to claim 1, wherein the ion-conducting membrane has a wet membrane average domain spacing (Å) as determined by small-angle X-ray scattering of less than or equal to about 34.

3. An ion-conducting membrane according to claim 1 or claim 2, wherein the ion- conducting membrane has a wet membrane correlation length (Å) as determined by small- angle X-ray scattering of less than or equal to about 9.

4. An ion-conducting membrane 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.

5. An ion-conducting membrane according to any preceding claim, wherein the sulphonated hydrocarbon ionomer has an ion-exchange capacity of less than or equal to about 5 meq / g.

6. An ion-conducting membrane according to any preceding claim, further comprising a reinforcing layer comprising a porous polymer material, wherein the ionomer is impregnated within the porous polymer material.

7. An ion-conducting membrane according to claim 6, having a Lambda value of less than about 30.

8. A catalyst-coated membrane for a fuel cell or a water electrolyser comprising an ion- conducting membrane according to any of the preceding claims, with a cathode catalyst layer applied to a first face of the membrane and / or an anode catalyst layer applied to a second face of the membrane.

9. A catalyst-coated membrane according to claim 8, wherein the catalyst layer comprises a perfluorosulphonic acid ionomer.

10. A catalyst-coated membrane according to claim 9, wherein the catalyst layer comprises a sulphonated hydrocarbon ionomer.

11. A membrane-electrode assembly for a fuel cell or a water electrolyser comprising (i) an ion-conducting membrane according to any of claims 1 to 7; or (ii) a catalyst-coated membrane according to any of claims 8 to 10; and at least one of a gas diffusion layer or a porous transport layer.

12. A water electrolyser or a fuel cell comprising a catalyst-coated membrane according to any of claims 8 to 10 or a membrane-electrode assembly according to claim 11.

13. A process of preparing an ion-conducting membrane according to any of claims 1 to 7, the process comprising casting the membrane from a mixture of the sulphonated hydrocarbon ionomer and a solvent.

14. A process according to claim 13, wherein the mixture has correlation length (Å) as determined by small-angle X-ray scattering of less than or equal to about 9.

15. A process according to claim 13 or claim 14, wherein the solvent comprises an alcohol which comprises 3 or more carbons.

16. A process according to any of claims 13 to 15, wherein the solvent comprises a main solvent and a second solvent.

17. A process according to any of claims 13 to 16, wherein the step of casting is carried out at ambient temperature.

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