Ionically conducting material for a membrane electrode assembly and uses thereof

Abstract

An adhesive material (7) adapted to be applied into any one of a proton exchange membrane (2), a catalyst layer (3, 4) and a gas diffusion electrode (5, 6) of membrane electrode assembly (1), wherein said adhesive material (7) comprises a colloidal dispersion of a cellulose nanomaterial, and wherein said adhesive material forms an interface layer between a membrane (2) and a gas diffusion electrode (5, 6) of a membrane electrode assembly.

Description

[0001] IONICALLY CONDUCTING MATERIAL FOR A MEMBRANE

[0002] ELECTRODE ASSEMBLY AND USES THEREOF

[0003] Technical field

[0004] The present invention relates to an ionically conducting material for a membrane electrode assembly, a membrane electrode assembly and uses thereof.

[0005] Background

[0006] Today’s challenges to meet the climate change include finding new materials and sources to substitute fossil fuels. One alternative source of fuel is hydrogen, which is converted to water, and energy, in a fuel cell. The fuel cell can be used in for instance vehicles or other applications, providing power for applications across multiple sectors, including transportation, industrial or commercial or residential buildings, and long-term energy storage for the grid in reversible systems. Fuel cells may also operate at higher efficiencies than conventional combustion engines and can convert the chemical energy in the fuel directly to electrical energy with efficiencies capable of exceeding 60%. A fuel cell comprises an anode and a cathode, sandwiched around an electrolyte membrane or membrane electrode assembly (MEA). A fuel, such as hydrogen, is fed to the anode, and air is fed to the cathode. In a hydrogen fuel cell, an at least a catalyst at the anode separates hydrogen molecules into protons and electrons, which take different paths to the cathode. The electrons go through an external circuit, creating a flow of electricity, which can be used for instance in an electrical vehicle. The protons migrate through the MEA to the cathode, where they unite with oxygen and the electrons to produce water and heat. The heart of the fuel cell is therefore the membrane electrode assembly, where the actual chemical reactions occur. The components, design and manufacture directly contributes to the quality and the cost of the fuel cell itself.

[0007] Conventionally, fuel cells membranes are made from a sulfonated tetrafluoroethylene based fluoropolymer-copolymer (brand name Nation™). This membrane material is both quite expensive, and also belongs to the class of per- and polyfluoroalkyl substances (PFAS), synthetic chemicals which are increasingly detected as environmental pollutants and also linked to negative effects on human health.

[0008] Therefore, alternatives to the conventional membranes have been discussed in literature, for instance in the article High temperature proton conduction in nanocellulose membranes: Paper fuel cells, Bayer, T et al, Chem. Mater, 2016, 28, 4805-4814, in which utilizing cellulose nanofibers in polymer electrolyte fuel cells (PEFCs) is investigated. In this article these nanocellulose membranes, some being chemically modified, are compared to conventional membranes, and are shown to exhibit excellent hydrogen barrier characteristics, acceptable proton conductivity, but quite low power density. In following articles, Bayer et al discuss spray coating sulfonated cellulose nanofibers as membrane material onto the gas diffusion electrode of the MEA, and hence increasing the power density if the MEA.

[0009] However, since there is a growing need to both increase the efficiency and cost of manufacturing fuel cells, and provide fuel cells that are more sustainable, there is a need for new and improved MEAs.

[0010] Summary

[0011] It is an object of the present disclosure, to provide an improved or alternative membrane electrode assembly, and an adhesive for use in such an assembly.

[0012] The invention is defined by the appended independent claims. Embodiments are set forth in the appended dependent claims and in the following description.

[0013] According to a first aspect there is provided an adhesive material adapted to be applied onto any one of a proton exchange membrane, a catalyst layer and a gas diffusion electrode (GDE) of membrane electrode assembly, wherein said adhesive material comprises a colloidal dispersion of a cellulose nanomaterial, and wherein said adhesive material forms an interface layer between a membrane and a gas diffusion electrode of a membrane electrode assembly.

[0014] In the present a novel and inventive component, i.e. the adhesive material forming an interface layer, of a MEA is thus disclosed which also provides for a MEA which has improved characteristics with regards to cost, performance and sustainability as compared to conventional Nafion™- based MEAs or other types of nanocellulose paper based MEAs. The adhesive material thus acts as an interface binder, or a sort of ionomer, between the membrane material and the catalyst layer, or catalyst coated GDE, or if the adhesive material comprises catalyst particles between the membrane and GDL, and ensures direct physical contact between the membrane and the electrodes, and enables undisrupted transport of electrons and protons in the “three-phase region”. The adhesive material is free from fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instace perfluorosulfonic acid (PFSA).

[0015] In one example, the gas diffusion electrode may be a coated catalyst gas diffusion electrode, i.e. provided with a catalyst or catalyst layer.

[0016] In one example, the catalyst layer may be a platinum catalyst.

[0017] In one example the adhesive layer may be substantially free from catalyst particles. This is a preferred embodiment of the present disclosure. This means that the adhesive material, forming the interface layer in for instance a MEA, is not what would be considered a catalyst layer per se, but a new component which adds to the efficiency and performance of the MEA.

[0018] In one example, the adhesive material further comprises catalyst particles and is adapted to be applied directly onto a gas diffusion layer (GDL). However, in such an example it is important to notice that that the material must be free from substances such as fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0019] In one example the cellulose nanomaterial may comprise, or consist of, cellulose nanofibrils, CNF; cellulose nanocrystals, CNC; and / or cellulose microfibrils, CMF; or a combination thereof. This means that in one preferred example, the adhesive material itself substantially may consist of or comprise cellulose nanofibrils.

[0020] In one example the cellulose nanomaterial may preferably consist of cellulose nanofibrils (CNF).

[0021] In one example the colloidal dispersion may further comprise additives, and wherein said additives is any one of a polymer, a mixture of polymers, nanoparticles, and a mixture of nanoparticles, or a combination thereof.

[0022] In one example the cellulose nanomaterial is chemically modified to exhibit, on surfaces of the nanomaterial any one of aldehyde groups, sulfo groups, carboxymethyl groups, phosphor groups and sulfoethyl groups.

[0023] In one example the adhesive material may be a colloidal cellulose dispersion having a concentration at 25°C and 85 % RH in the range of 2 to 15 g / l.

[0024] According to a second aspect there is provided a membrane electrode assembly, comprising a proton exchange membrane, at least one catalyst layer and at least two gas diffusion layers, and an adhesive material according to the first aspect arranged between said membrane and said catalyst layer or said catalyst coated gas diffusion electrode, thereby forming an interface layer, wherein said adhesive layer comprises a cellulose nanomaterial.

[0025] The novel and inventive component, i.e. the adhesive material, thus acts as an interface binder, or ionomer, between the membrane material and the catalyst layer, or catalyst coated GDE, or if the adhesive material comprises catalyst particles between the membrane and GDL, and ensures direct physical contact between the membrane and the electrodes, and enables undisrupted transport of electrons and protons in the “three-phase region”. It has surprisingly been shown that utilizing an adhesive material according to the first aspect provides for a MEAs having similar performance as assembled using a conventional Nation™ ionomer and the inventive cellulose nanofibril ionomer respectively, while providing for a more sustainable and environmentally friendly MEA, since they are completely free from substances such as fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0026] In one example of the second aspect, said proton exchange membrane and said adhesive material may be made from substantially the same cellulose nanomaterial composition. This further increases the sustainability of the MEA, as it can be made from renewable sources. Additionally, this means that a MEA can be produced which is completely free from substances such as fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0027] In one example said adhesive material, or interface layer, may be substantially free from catalyst particles. By substantially free is meant that no catalyst particles are added to the adhesive material, however due to migration between materials some catalyst particles may occur at least at the boundary region between the adhesive and catalyst layer of the GDE. This is considered a preferred embodiment.

[0028] In one example said adhesive material, or interface layer, comprises catalyst particles. In this example, no additional adhesive material may be needed to ensure the direct contact between the membrane and the GDE. However, in this example, it is important to notice that the adhesive material does not comprise substances such as fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0029] In one example the adhesive material or interface layer may be arranged such that it ensures direct physical contact between the membrane and the electrodes. According to a third aspect there is provided a fuel cell comprising a membrane electrode assembly as according to the second aspect. The fuel cell has surprisingly been shown the exhibit fuel cell polarization curves having similar performance using a conventional Nation™ ionomer and the inventive cellulose nanofibril ionomer respectively.

[0030] According to a fourth aspect there is provided a method of manufacturing a membrane electrode assembly, wherein said method comprises: providing a membrane; providing any one of a gas diffusion electrode, a catalyst layer and a gas diffusion layer; applying an adhesive material according to the first aspect on either one of the membrane or any one of said gas diffusion electrode, said catalyst layer and said gad diffusion layer, or a combination thereof; arranging a first gas diffusion electrode on a first side of the membrane and a second gas diffusion electrode on a second side of the membrane; pressing said gas diffusion electrodes and membrane together, such that said adhesive material is arranged between said membrane and said catalyst coated gas diffusion electrodes or catalyst layer, thereby forming an interface layer, and wherein said adhesive material comprises an colloidal dispersion of a cellulose nanomaterial.

[0031] According to a fifth aspect there is provided the use of a membrane electrode assembly according to the second aspect, or the membrane electrode assembly as obtained by the method according to the fourth aspect in a fuel cell.

[0032] Brief description of drawings

[0033] Embodiments of the present solution will now be described, by way of example, with reference to the accompanying schematic drawings.

[0034] Figs 1 shows an exemplary exploded view of an exemplary membrane electrode assembly. Fig. 2 shows an exemplary side view of an exemplary membrane electrode assembly.

[0035] Fig. 3 shows a graph of a comparison between a membrane comprising a conventional (Nation™) ionomer and an ionomer according to one example of the present disclosure.

[0036] Description of Embodiments

[0037] Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout the description.

[0038] As used herein, and in accordance with the TAPPI document “Roadmap for the Development of International Standards for Nanocellulose” of October 24, 2011 , as well as the ISO TC 229 protocols, the term “cellulose nanomaterials” includes plant-based nanocellulose as well as nanocellulose from bacteria, algae, tunicates, and other sources. Examples of nanocellulose, and thus of cellulose nanomaterials, include herein mentioned cellulose nanofibrils (CNF), cellulose nanocrystals (CNC) and cellulose microfibrils (CMF).

[0039] In general, membrane electrode assembly can be described or categorized as either the membrane and the electrodes, or a five-layer configuration comprising the membrane, catalyst layers and gas diffusion media layers. In this disclosure, the MEA will generally be referred to and described as the five-layer configuration, however the catalyst particles may also be incorporated into the gas diffusion electrode.

[0040] Conventionally, in a PEMFC (proton-exhange membrane fuel cell) the MEA membrane comprises a Nation™ material, i.e. a per- and polyfluoroalkyl substance (PFAS), which is hot pressed between two gas diffusion electrodes, or catalyst coated gas diffusion electrodes. A drawback of this manufacturing method is also that the Nation™ membrane is sensitive to heat and may swell or delaminate. A conventional MEA can be manufactured according to the following steps: Coat a thin layer of catalyst, typically platinum, onto both sides of a proton exchange membrane (e.g., Nation™) to form a catalyst coated membrane (CCM). A hot-pressing technique is then used to bond gas diffusion layers (typically made of carbon cloth or carbon paper) onto the catalyst-coated surfaces. In this process it is important to ensure proper alignment and uniform pressure during the hot-pressing process to create a well-bonded MEA.

[0041] In the alternative the catalyst layer can be coated onto the diffusion media instead, and such a MEA is called a catalyst coated substrate (CCS). Additionally, when using Nation, i.e. per- and polyfluoroalkyl substances (PFAS) based, membranes, an intermediate step can be introduced in making CCM type MEAs, where the electrodes can be cast on a temporary substrate such as Teflon (which also belong to the PFAS group chemicals), an then be hot pressed onto a membrane after which the Teflon layer is removed, this method is called the “decal transfer method”.

[0042] The gas diffusion layers (GDL) are arranged outside the catalyst layers and facilitate transport of reactants into the catalyst layer, as well as removal of product water. Each GDL may typically composed of a sheet of carbon paper in which the carbon fibers are partially coated with polytetrafluoroethylene (PTFE). The GDL is made up of two layers, a macroporous layer and a microporous layer. In the macroporous layer the diffusion media has been treated with a hydrophobic agent (such as PFTE), to prevent flooding of the channels in the diffusion media. The microporous layer aids in managing the water content of the MEA, and is also much thinner than the macroporous layer. Gases diffuse rapidly through the pores in the GDL. The microporous layer can thus help adjust the balance between water retention (needed to maintain membrane conductivity) and water release (needed to keep the pores open so hydrogen and oxygen can diffuse into the electrodes).

[0043] The membrane, catalyst layers (anode and cathode), and diffusion media thus together form the membrane electrode assembly (MEA) of a PEM fuel cell. Some of the most important aspects of Proton Exchange Membrane Fuel Cell (PEMFC) manufacturing include the catalyst coating, since the deposition of the catalyst material (usually platinum or platinum alloy) must be precise and uniform onto the membrane and gas diffusion layers is crucial for optimal electrochemical reactions. Controlling catalyst loading and distribution is essential to ensure efficient performance. An ionomer, or dispersion, conventionally act as a binder agent such as securing the catalyst particles either on the surface of the gas diffusion layers or on the surface of the membranes. Previously PFTE has often been used as a binder for the catalyst particles, but has more and more been replaced by compositions such a Nation™ , i.e. per- and polyfluoroalkyl substances (PFAS), as an ionomer to bind the catalyst particles, and these electrodes are called thin film electrodes.

[0044] Secondly, the proton exchange membrane (PEM), must be carefully prepared to ensure consistent thickness, appropriate proton conductivity, and sufficient mechanical strength. Membrane handling and storage conditions are critical to prevent drying or damage.

[0045] Thirdly, since the gas diffusion layers facilitate reactant gas distribution and provide electrical conductivity, ensuring a proper bonding between GDLs and the membrane / catalyst layers is essential for effective gas transfer and electron flow.

[0046] Further to this in conventional MEA preparation, the hot-pressing or lamination step need to be carefully controlled, by applying controlled heat and pressure, in order to ensure a good contact between the catalyst, membrane, and GDLs, promoting efficient reactant supply and current collection.

[0047] The interfaces between the MEA components and the three phase boundary between the reactant, the catalyst and the ionomer thus directly determine the performance of the fuel cell. An ionomer or dispersion conventionally act as a binder agent such as securing the catalyst particles either on the surface of the gas diffusion layers or on the surface of the membranes. An ionomer is an ion containing copolymer, containing both nonionic repeat units, and a small amount of ion containing repeat units (usually less than 15 %).

[0048] In the present disclosure a novel and inventive component of a MEA as well as new and inventive way of manufacturing a MEA, is disclosed in order to provide a MEA which has improved characteristics with regards to cost, performance and sustainability as compared to conventional Nafion™-based MEAs or other types of nanocellulose paper based MEAs.The component is substantially free from fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0049] Fig. 1 illustrates a membrane electrode assembly (MEA) 1. A basic MEA assembly 1 comprises a proton-exchange membrane (PEM) 2, sandwiched between gas diffusion electrodes (GDE) 5, 6, applied to each side of the membrane 2. The gas diffusion electrodes 5, 6 may be coated with a catalyst layer 3, 4. The catalyst layer may further be coated onto a gas diffusion layer (GDL) or material, thus forming the GDE. The catalyst particles may also be embedded into the electrodes. The terminology used herein may thus include that the gas diffusion electrode may be coated with a catalyst layer, which layer is in contact with the PEM, and that the adhesive material 7 is arranged between the PEM and the electrode, or the catalyst layer, or that the adhesive material 7 is coated onto GDL. In one example, the adhesive material 7 may be applied onto a GDE with embedded catalyst particles. The terminology will hence depend on the constituents of the adhesive material, and the manufacturing method of the MEA. In a preferred embodiment the adhesive material 7 is free from from fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA) as well as catalyst particles.

[0050] According to the present disclosure in the manufacturing of the MEA 1 , a layer of the novel and inventive adhesive material 7 is applied onto any one or both sides of the membrane 2, onto any one or both of the catalyst layers 3, 4, or onto any one or both gas diffusion electrodes 5, 6, such that the adhesive layer or material 7 is arranged between the membrane 2 and the gas diffusion electrodes 5, 6. The adhesive material 7 thus forms an interface layer, which is a novel and inventive component in the MEA. The adhesive material 7 may in general not comprise any catalyst particles, but instead act only as an interface binder, or ionomer, between the membrane material and the catalyst layer / the catalyst coated gas diffusion electrode. The inventive adhesive material 7 thus forms an interface binder layer and ensures direct physical contact between the membrane and the electrodes, and enables undisrupted transport of electrons and protons in the “three-phase region”. The adhesive material 7 is thus an ionically conducting material.

[0051] In one example, the adhesive material 7 may however comprise catalyst particles and may thus be provided directly onto a gas diffusion layer or material, which is a part of a gas diffusion electrode. In the present disclosure the gas diffusion layer or the gas diffusion electrode are represented by the same reference numerals. The inventive adhesive material 7 thus forms an interface binder layer and ensures direct physical contact between the membrane and the electrodes. In this example it is however important that the material does not comprise substances from fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0052] Platinum is one of the most commonly used catalysts, however other platinum group metals may also used. Ruthenium and platinum may also be used together.

[0053] Fig. 2 schematically illustrates in a side view the MEA 1 comprising a membrane 2, at least one catalyst layer 3, 4 and at least two layers of gas diffusion material 5, 6, or gas diffusion electrodes 5, 6 of Fig. 1 , where the adhesive layer 7 is arranged as an interface layer or interface binder layer between the membrane 2 and gas diffusion electrodes.

[0054] The adhesive material 7 comprises, or consist of, a colloidal dispersion comprising a cellulose nanomaterial. This means that the main adhesive material can be manufactured completely from renewable and sustainable sources, and thus has a minimal impact on the environment. In one example, the adhesive material may comprise additives, such as polymers or other types of nanomaterials.

[0055] The cellulose nanomaterial comprises or consists of CNF, CNC, and / or CMF. In some preferred examples, the cellulose nanomaterial of the adhesive material comprises or consists of CNF. In one preferred example, the cellulose nanomaterial comprises or consists of a chemically modified, or functionalized, CNF.

[0056] The colloidal dispersion is free from fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0057] The adhesive material comprises, or consists of, a colloidal dispersion of cellulose nanomaterial, which preferably has a concentration in the range of 5 to 15 g / l. More preferably the concentration is in the range of 8 to 12 g / l. In one example the concentration of cellulose dispersion is about 10 g / l. By the expression “consist of” here is meant that the adhesive material or the interface binder layer substantially only comprises the cellulose nanomaterial itself. It may in one example, also comprise other additives, and in one example those additives are only present in minor amounts.

[0058] The colloidal cellulose dispersion may thus be used as a glue or adhesive during the MEA preparation, and subsequently forms or acts as an interface layer, or an interface binder layer between the membrane and the GDE, or between the membrane and the GDL. In one example the adhesive material may comprise catalyst particles, and act as a binder layer between the membrane and the GDL.

[0059] In one embodiment the membrane 2 is made from the same material as the adhesive material 5 or colloidal cellulose dispersion. This means that a MEA may be manufactured or produced which is substantially free from fluoropolymer materials, specifically per- and polyfluoroalkyl substances (PFAS), such as for instance perfluorosulfonic acid (PFSA).

[0060] In one example, the membrane 2 may be formed from the same starting material (or colloidal dispersion) as the adhesive material, but may when dry, consists to 100% of a crosslinked cellulose nanomaterial, which is described in further detail below. This means that the membrane material undergoes a crosslinking procedure, where at least one additive is a crosslinking agent. In one example, the cellulose nanomaterial is chemically modified to exhibit, on surfaces of the nanomaterial any one of aldehyde groups, sulfo groups, carboxymethyl groups, phosphor groups and sulfoethyl groups. This means that the cellulose nanomaterial may be functionalized with any one of any one of aldehyde groups, sulfo groups, carboxymethyl groups, phosphor groups and sulfoethyl groups. This means that the CNF is functionalized.

[0061] In one example, the membrane 2 is formed from a functionalized CNF having a specific functionalization, while the adhesive material 7 is formed from a functionalized CNF having the same or different functionalization. The functionalization of the CNF may thus be adapted for the specific purpose of the CNF (i.e. membrane or interface layer).

[0062] In one example of the present disclosure, the cellulose nanomaterial is chemically modified to exhibit, on surfaces of the nanomaterial, aldehyde groups [-CHO] within the range of 0.5-1 mmol / g dry nanomaterial, preferably within the range of 0.7-0.9 mmol / g, as determined by titration. For instance, the titration may be performed by reacting the aldehyde groups of a sample of the material with a known dry weight with hydroxylamine, typically provided as hydroxylamine hydrochloride, at a specific pH (e.g. pH 4) which reaction releases a stochiometric amount of protons, lowering the pH. By performing a regular acid-base titration back to the specific pH, the number of aldehyde groups in the sample is determined. It should be noted that this relates to the amount of aldehyde groups remaining after the sulfonation. The total amount of introduced aldehyde groups prior to sulfonation is thus this remaining amount plus the amount of sulfo groups. The aldehydes may be introduced by oxidation, e.g. of cellulose fibres or nanocellulose such as CNF, by means of sodium metaperiodate (NalO4). In some embodiments, the amount of NaIC is within the range of 1 -3 g / g dry fibre.

[0063] The aldehyde groups can contribute to a desired negatively charged environment by facilitating introduction of acidic substituent groups, e.g. sulfo groups [-S(=O)2-OH] .

[0064] To introduce sulfo-groups, at least some of the aldehyde groups exhibited on the surfaces of the nanomaterial can be sulfonated, e.g. by means of sodium metabisulfite (Na2S20s). In some embodiments, the amount of Na2S20s is within the range of 0.5-2.5 g / g dry fibre.

[0065] In one example of the present disclosure, the cellulose nanomaterial is chemically modified to exhibit, on surfaces of the nanomaterial, sulfo groups in an amount providing a charge within the range of 200-1500 pmol / g nanomaterial, preferably within the range of 300-1400 pmol / g, as determined by titration in accordance with Katz “Determination of strong and weak conductometric acidic groups in sulphite pulps” of 1984.

[0066] Also the sulfo groups may be negatively charged [-S(=O)2-O_] further contributing to a desired negatively charged environment.

[0067] Alternatives to the use of Na2S20s for introducing the sulfo groups are envisioned. For instance, an amine containing reagent may be used, e.g. sulfanilic acid and / or taurine. The amine can react with an aldehyde group to form imine which may then be reduced, e.g. by means of sodium borohydride, to form a stable amine, whereby the sulfo group would then be attached to the nanomaterial via the amine.

[0068] In other examples of the present disclosure, carboxym ethylated, phosphorylated and / or sulfonated cellulose nanofibrils may be used in the colloidal cellulose dispersion.

[0069] The dispersion may further comprise additives, and wherein said additives is any one of a polymer, a mixture of polymers, nanoparticles, and a mixture of nanoparticles, or a combination thereof.

[0070] As mentioned above, the membrane 2 may be formed from the same material the adhesive material, but may when dry, consists to 100% of the crosslinked cellulose nanomaterial.

[0071] However, in other embodiments, the membrane 2 may comprise the cellulose nanomaterial in combination with another nanomaterial.

[0072] The membrane 2 may, when dry, have a thickness within the range of 5-100 pm.

[0073] The membrane 2 may, when dry, have a density within the range of 1 .2-1 .6 g / cm3, preferably within the range of 1 .4-1 .5 g / cm3, which is close to the density of pure cellulose. Trials

[0074] MEA preparation

[0075] Two pieces of a commercial platinum gas diffusion electrode (GDE) were cut into 2.2x2.2 cm size. The adhesive material, i.e. the colloidal cellulose dispersion with a concentration of 2-10 g / l, was placed on one side of a membrane and a piece of the Pt-GDE was added. The materials were hot- pressed at a temperature of 70°C for about 60 seconds. The adhesive material, i.e. the cellulose solution was placed on the other side of the membrane and the second piece of Pt-GDE was added while keeping the two Pt-GDE aligned. The assembly was hot-pressed once more at 70°C for 60 seconds.

[0076] Fuel cell protocol

[0077] The MEA was placed on the cell fixture. Room temperature was kept and dry condition was applied (80 % RH at 40°C). A 20 minute flow of nitrogen on both the anode and cathode was applied, and then a change to hydrogen and air gas respectively. The Pt-GDEs were activated at 300 mV.

[0078] Results

[0079] The colloidal cellulose dispersion worked well as adhesive material during the MEA preparation, and as an intermediate or interface binder (ionomer). Water present in the adhesive material does not seem to affect the material or dissolve it. There was no visual change of the membrane during the hot-press application.

[0080] In Fig. 3 a comparison between a conventional MEA incorporating Nation (membrane_SE_Nafion) and a MEA incorporating only sulfoethylated cellulose nanofibrils (membrane_SE) as the adhesive layer or interface binder is shown. The fuel cell polarization curves for the MEAs show similar performance assembled using the Nation ionomer and the cellulose ionomer respectively. Modifications and other variants of the described embodiments will come to mind to one skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure. Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms “com prise / com prises” or “include / includes” do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a combination of features is not feasible and / or advantageous. In addition, singular references do not exclude a plurality. Finally, reference signs in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims

CLAIMS1 . An adhesive material (7) adapted to be applied into any one of a proton exchange membrane (2), a catalyst layer (3, 4) and a gas diffusion electrode (5, 6) of membrane electrode assembly (1 ), wherein said adhesive material (7) comprises a colloidal dispersion of a cellulose nanomaterial, and wherein said adhesive material forms an interface layer between a membrane (2) and a gas diffusion electrode (5, 6) of a membrane electrode assembly.

2. The adhesive material (7) as claimed in claim 1 , wherein said gas diffusion electrode (5, 6) is coated with a catalyst layer.

3. The adhesive material as claimed in any one of claims 1 or 2, wherein said catalyst layer (3, 4) comprises a platinum catalyst.

4. The adhesive material (7) as claimed in claim 1 , wherein said adhesive material further comprises catalyst particles and is further adapted to be applied directly onto a gas diffusion layer (5, 6).

5. The adhesive material (7) as claimed in any one of claims 1 to 4, wherein said cellulose nanomaterial comprises or consists of cellulose nanofibrils, CNF; cellulose nanocrystals, CNC; and / or cellulose microfibrils, CMF; or a combination thereof.

6. The adhesive material (7), as claimed in any one of claims 1 -4, wherein said colloidal dispersion further comprises additives, and wherein said additives is any one of a polymer, a mixture of polymers, nanoparticles, and a mixture of nanoparticles, or a combination thereof.

7. The adhesive material (7) as claimed in any one of claims 1 to 5, wherein the cellulose nanomaterial is chemically modified to exhibit, on surfaces of the nanomaterial any one of aldehyde groups, sulfo groups, carboxymethyl groups, phosphor groups and sulfoethyl groups.

8. The adhesive material (7) as claimed in any one of claims 1 to 6, wherein said adhesive material is a colloidal cellulose dispersion having a concentration at 25°C and 85 % RH in the range of 2 to 15 g / l.

9. The adhesive material (7) as claimed in any one of the preceding claims, wherein the adhesive material (7) is free from fluoropolymer materials, such as per- and polyfluoroalkyl substances (PFAS).

10. A membrane electrode assembly (1 ), comprising a proton exchange membrane (2), at least one catalyst layer (3, 4) and at least one gas diffusion electrode (5, 6), and an adhesive material (7) according to any one of claims 1 to 8 arranged between said membrane and said catalyst layer (3, 4) or said gas diffusion electrode (5, 6), thereby forming an interface layer, wherein said adhesive layer (7) comprises a cellulose nanomaterial.11 . The membrane electrode assembly as claimed in claim 10, wherein said proton exchange membrane (2) and said adhesive material (7) are made from substantially the same cellulose nanomaterial composition.

12. The membrane electrode assembly as claimed in any one of claims 10 to 11 , wherein said adhesive material (7), or interface layer, is substantially free from catalyst particles.

13. The membrane electrode assembly as claim in any one of claim 10 to12, wherein the adhesive material (7) or interface layer is arranged such that it ensures direct physical contact between the membrane (2) and the at least one gas diffusion electrode (5, 6).

14. A fuel cell comprising a membrane electrode assembly as claimed in any one of claims 10 to 13.

15. A method of manufacturing a membrane electrode assembly (1 ), wherein said method comprises: providing a membrane (2); providing any one of a catalyst layer (3, 4), a gas diffusion electrode (5, 6), a catalyst coated gas diffusion electrode (5, 6) and a gas diffusion layer (5, 6); applying an adhesive material (7) on either one of the membrane (2) or onto any one of said catalyst layer (3, 4), said gas diffusion electrodes (5, 6), said catalyst coated gas diffusion electrode (5, 6); and said gas diffusion layer (5, 6); or a combination thereof; arranging a first gas diffusion electrode (5) on a first side of the membrane (2) and a second gas diffusion electrode (6) on a second side of the membrane (2); pressing said gas diffusion electrodes (5, 6) and membrane (2) together, such that said adhesive material (7) is arranged between said membrane (2) and said gas diffusion electrode (5, 6) or catalyst layer (3, 4), thereby forming an interface layer, and wherein said adhesive material (7) comprises an colloidal dispersion of a cellulose nanomaterial.

16. The use of a membrane electrode assembly (1 ) according to any one of claims 10 to 14, or the membrane electrode assembly (1 ) as obtained by the method according to claim 15 in a fuel cell.

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