Membrane group with catalytic coating for membrane electrode assemblies, electrolyzer comprising said membrane group and method for producing such membrane group

Abstract

The present invention concerns a membrane group (1) with catalytic coating for membrane electrode assemblies comprising : a polymer electrolyte membrane (10), preferably a proton-conducting polymer electrolyte membrane, on which a first face (11) is identified, intended in use to define the anodic side, and a second face (12), opposite the first and intended in use to define the cathodic side in a membrane electrode assembly; and a catalytic layer (20), preferably based on iridium, associated with one of said faces (11, 12) of the membrane (10), preferably being intended in use to function as an anode. The membrane group (1) comprises a porous layer of conductive material (30) which is placed to cover said catalytic layer (20). The conductive material layer (30) comprises at least one electron- conducting organic polymer. The membrane (10), the catalytic layer (20), and the porous layer of conductive material (30) form a single body.

Description

"MEMBRANE GROUP WITH CATALYTIC COATING FOR MEMBRANEELECTRODE ASSEMBLIES , ELECTROLYZER COMPRISING SAID MEMBRANE GROUP AND METHOD FOR PRODUCING SUCH MEMBRANE GROUP" DESCRIPTIONField of the invention

[0001] The subj ect of the present invention is a membrane group with catalytic coating for membrane electrode assemblies , an electrolyzer comprising said membrane group and a method for producing such membrane group .

[0002] The membrane group with catalytic coating for membrane electrode assemblies according to the invention finds particular application in electrolyzers (Water Electrolyzers ) , but may also find application in other electrochemical devices using membrane electrode assemblies (MEA) , in particular fuel cells ( Fuel Cells ) . Prior art

[0003] A membrane electrode assembly, better known in the field as MEA (Membrane Electrode Assembly) , comprises :

[0004] - a membrane , typically polymeric, for example of the type of ionic conductivity polymer electrolyte ,

[0005] - an anode positioned on a first face of the membrane ( for example in the form of a layer with catalyst and ionomer, also called anodic catalytic layer ) ,

[0006] - a cathode positioned on a second face of the membrane ( for example in the form of a layer with catalyst and ionomer, also called cathodic catalytic layer ) .

[0007] Generally, such assemblies (MEA) are used in fuel cells and electrolyzers , as components of an assembled stack .

[0008] The membrane is inserted between two electrodes that contain the catalyst . The electrodes are electrically insulated from each other by the membrane and respectively constitute the anode and the cathode .

[0009] The polymer membrane is typically an electrically insulating barrier selectively permeable to ions , for example made of perfluorosul fonic acid ( PFSA) ionomers . In the case of a membrane made with an anion-conducting polymer, the membrane is called an AEM - Anion Exchange Membrane . In the case of a membrane made with a protonconducting polymer, the membrane is called a PEM - Proton Exchange Membrane .

[0010] In the assembled stack that composes a fuel cell or an electrolyzer, on both sides of the MEA there is a porous transport layer, known in the field as PTL ( Porous Transport Layer ) or GDL ( Gas Di f fusion Layer ) .

[0011] Each electrode consists of a catalytic layer that can be associated either with the membrane itsel f( forming a so-called membrane group ) or alternatively with the respective porous transport layer .

[0012] In electrolysis , hydrogen and oxygen are produced from water using electrical energy . Polymer membrane electrolyzers comprise one or more membrane electrode assemblies (MEA) . In the catalytic layers the chemical reactions occur, and the gases are produced therein . Through the PTL transport layers , which may also be defined as di f fusion layers , the water supply, the gas outflow and the electrical contact take place .

[0013] An MEA allows to establish a three-phase boundary, anodic or cathodic, essential for the establishment of the transport phenomena necessary for the operation of electrolyzers and fuel cells .

[0014] In the case of proton conductivity polymer electrolyte electrolyzers ( PEMWE ) , the anodic three-phase boundary is the interface where the anode electrode , the reactant (H2O) , and the polymer electrolyte ( PEM) meet . At this boundary, water is oxidi zed producing protons (H+ ) , electrons and oxygen . The protons are transported across the membrane to the cathode , while the electrons flow on the available paths in the external circuit . The ef ficiency of this process depends on the quality of the anodic three-phase boundary, which is inf luenced by factors such as the distribution of the catalyst , themass transport of water through the electrode, and the transport of gaseous oxygen out of the electrode.

[0015] In proton conductivity polymer electrolyte electrolyzers (PEMWE) , the cathodic three-phase boundary is, instead, the interface where the cathode electrode, protons (H+) , and electrons meet. At this boundary, protons and electrons combine to produce gaseous hydrogen. The efficiency of this process also depends on the quality and distribution of the cathodic three-phase boundary .

[0016] The three-phase boundaries are therefore fundamental for the transport phenomena occurring within an electrolyzer because their distribution and accessibility determine the transfer of reagents, products, and charge between the electrodes and the membrane. The efficiency of these processes depends on the quality of the interfaces and the transport properties of the materials involved. Therefore, the optimization of the three-phase boundaries is essential to improve the performance of electrolyzers.

[0017] The same issues of the three-phase boundary are also present in polymer electrolyte fuel cells, with the difference that at the anode hydrogen is oxidized producing electrons and protons (H+) , while at the cathode oxygen is reduced with the production of water.

[0018] In particular, in acidic electrolysis, protons migrate through the membrane as charge carriers. The polymer membrane is made of a proton-conducting polymer, e.g., perfluorosulfonic acid (PFSA) . Acidic electrolysis is also called PEM electrolysis (with proton exchange membrane) . The catalytic layers are usually made of nanoparticles, e.g., IrOx or IrRuOx on the anodic side and platinum on carbon on the cathodic side, each with a proton-conducting polymer (e.g., PFSA-based) as binder. The transport layers are usually made of a non-woven titanium fiber fabric, a sintered titanium or an expanded titanium mesh (on the anodic side) and a carbon fiber cloth (on the cathodic side) .

[0019] A key object for the next generation of proton conductivity polymer electrolyte electrolyzers PEMWE is the reduction of the catalyst loading in order to both reduce costs and mitigate the possibility of future shortages in the supply of the catalyst, constituted for example by iridium, a critically scarce material.

[0020] Currently, the state of the art of the technology in the field of electrolyzers is based on a catalyst-coated membrane platform (membrane group) . In this configuration, a catalytic layer based on iridium is deposited on a proton exchange membrane (PEM) to form the anodic electrode. Various direct and indirect inkdeposition techniques have been developed to obtain a uni form and evenly distributed iridium layer ( JP6225890B2 ) . However, all developed techniques fail to achieve desirable properties in terms of both performance and durability when attempting to reduce the iridium catalyst loading below 0 . 5 mg- cm”2. Currently, the lower limit reached is around 2 mgmm'2.

[0021] Recent studies have identi fied the formation of islands and / or disconnected zones in the electrode as one of the main limiting mechani sms . These islands and / or disconnected zones are generated by local deformations of the membrane and by the dissolution of iridium during operation and cause the iridium layer to fragment into multiple pieces . When one of these fragments loses electrical connection with the interface of the porous transport layer and with the remaining part of the catalytic layer, it becomes electrically isolated and ceases to function, ef fectively deactivating the corresponding section of the anodic electrode .

[0022] This issue is speci fically addressed in patent application US2022 / 0307141 Al . It is proposed to interpose an intermediate layer consisting of conductive ceramic or metallic nanofibers between at least one catalytic layer formed of nanoparticles and the respective porous transport layer . Alternatively, it isproposed to introduce the conductive ceramic or metallic nanofibers directly into the catalytic layer . The increase in conductivity at the interface between the catalytic layer and the membrane results in an increase in the electrical connectivity of the catalytically active nanoparticles , leading to increased conductivity at the interface . Moreover, the nanofibers can reduce the contact resistance between the transport layer and the catalytic layer and further reduce mass transport resistance by increasing porosity .Disclosure of the invention

[0023] Therefore , the main obj ect of the present invention is to provide an alternative solution to that of the above-cited known technique , by providing a membrane group with catalytic coating for membrane electrode assemblies capable of ensuring the electrical connectivity of the associated catalytic layer once said membrane group is inserted into a membrane electrode assembly and associated with the respective porous transport layers .

[0024] A further obj ect of the present invention is to provide a membrane group with catalytic coating for membrane electrode assemblies that is easy to make .Brief description of the Figures

[0025] The technical features of the invention, accordingto the above-mentioned obj ects , are clearly apparent from the content of the claims below, and the advantages thereof will be more evident in the detailed description that follows , made with reference to the accompanying drawings , which represent one or more purely illustrative and non-limiting embodiments thereof , wherein :

[0026] - Figure 1 shows a schematic representation not to scale of a membrane group with catalytic coating for membrane electrode assemblies according to a preferred embodiment of the invention;

[0027] - Figure 2 shows a schematic representation not to scale of the membrane group with catalytic coating of Figure 1 , illustrated in association with a porous transport element on the anodic side according to a first embodiment of assembly;

[0028] - Figure 3 shows a schematic representation not to scale of the membrane group with catalytic coating of Figure 1 , illustrated in an integrated condition in a membrane electrode assembly MEA, in turn associated with two porous transport elements respectively provided on the anodic and cathodic sides according to a first embodiment of assembly, particularly forming an assembled stack of an electrolyzer ;

[0029] - Figure 4 shows a schematic representation not to scale of the membrane group with catalytic coating ofFigure 1 , illustrated in association with a porous transport element on the anodic side according to a second embodiment of assembly; and

[0030] - Figure 5 shows a schematic representation not to scale of the membrane group with catalytic coating of Figure 1 , illustrated in an integrated condition in a membrane electrode assembly MEA, in turn associated with two porous transport elements respectively provided on the anodic and cathodic sides according to a second embodiment of assembly, particularly forming an assembled stack of an electrolyzer .Detailed description

[0031] A membrane group with catalytic coating for membrane electrode assemblies according to the invention is overall denoted by number 1 in the attached Figure 1 .

[0032] A membrane electrode assembly MEA (Membrane Electrode Assembly) , intended to be integrated into an assembled stack of an electrolyzer or a fuel cell ( as illustrated in Figures 3 and 5 ) , comprises :

[0033] - a membrane 10 , in particular polymeric ( for example of the type of polymer electrolyte with ionic conductivity) ;

[0034] - an anode 20 positioned on a first face of the membrane ;

[0035] - a cathode 200 positioned on a second face of themembrane .

[0036] In other words , in a membrane electrode assembly MEA, the membrane 10 is inserted between two electrodes 20 and 200 that contain the catalyst . The electrodes 20 and 200 are electrically insulated from each other by the membrane and respectively constitute the anode and the cathode . In turn, each electrode consists of a catalytic layer .

[0037] Within an assembled stack that forms an electrolyzer or a fuel cell , in addition to one or more MEAs , there may be other components ( such as gaskets and bipolar plates ) which, for the sake of simplicity, are not listed here , also considering that the application of the membrane group with catalytic coating 1 according to the present invention is not limited to the type of assembled stack and its speci fic components .

[0038] In particular, in an assembled stack each catalytic layer present in an MEA is associated with a porous transport layer 40 and 400 , known in the field as PTL ( Porous Transport Layer ) or GDL ( Gas Dif fusion Layer ) .

[0039] According to a general embodiment of the invention, the membrane group 1 comprises a polymer electrolyte membrane 10 , preferably a proton-conducting polymer electrolyte membrane .

[0040] In the case of a membrane made with a proton-conducting polymer, the membrane is called PEM ProtonExchange Membrane .

[0041] In particular, the PEM proton-conducting polymer membrane can be made of perfluorosul fonic acid ( PFSA) ionomers . The most commonly used PFSAs in PEMs are commercially known as Nafion and Aquivion .

[0042] On said membrane 10 , a first face 11 is identi fied, intended in use to define the anodic side , and a second face 12 , opposite the first and intended in use to define the cathodic side , in a membrane electrode assembly .

[0043] The membrane group 1 comprises a catalytic layer 20 , associated with one of said faces 11 , 12 of the membrane 10 . Preferably, said catalytic layer 20 is intended in use to function as an anode and is associated with the first face 11 of the membrane .

[0044] Preferably, the catalytic layer 20 is based on iridium . In particular, the catalytic layer can be constituted by nanoparticles , e . g . , o f IrOx or IrRuOx .

[0045] According to the invention, as illustrated in Figure 1 , the membrane group 1 compri ses a porous layer of conductive material 30 which is placed to cover said catalytic layer 20 so as to be interposed in use between said catalytic layer 20 and a porous transport layer 40 .

[0046] Said porous layer of conductive material 30 comprises at least one electron-conducting organicpolymer .

[0047] The membrane 10 , the catalytic layer 20 , and the porous layer of conductive material 30 form a single body .

[0048] Advantageously, thanks to the invention, the membrane group 1 ensures the electrical connectivity of the associated catalytic layer once the membrane group 1 is inserted into a membrane electrode assembly and associated with the respective porous transport layers , thus providing an alternative solution to that of the above-cited known technique .

[0049] Indeed, it has been experimentally veri fied that the presence of the porous layer of polymer-type conductive material , interposed between the catalytic layer and the porous transport layer, reduces the loss of active portions in the catalytic layer as a result of the formation of possible fragments . This signi ficantly reduces the risk of formation of islands and / or disconnected zones in the coated electrode and thus the risk of locally losing the electrical connection with the interface of the porous transport layer and with the remaining part of the catalytic layer .

[0050] The porous layer of polymer-type conductive material thus leads to an increase in conductivity at the interface between the catalytic layer of the membranegroup and the porous transport layer, which results in an increase in the electrical connectivity of the catalytically active particles , leading to increased conductivity at the interface . This makes it possible to reduce the catalyst ( iridium) loading .

[0051] According to the invention, the porous layer of conductive material 30 is placed to cover the catalytic layer 20 on the side opposite to the polymer electrolyte membrane 10 .

[0052] According to a preferred embodiment of the invention, the porous layer of conductive material 30 comprises at least one ion-conducting organic polymer in addition to said at least one electron-conducting organic polymer . In other words , preferably, the porous layer of conductive material 30 comprises a mixture of ionconducting polymer material and electron-conducting polymer material .

[0053] Advantageously, said porous layer of conductive material 30 is integral with the catalytic layer 20 .

[0054] In particular, the porous layer of conductive material 30 may be obtained by depositing the polymeric materials constituting it in the form of fibers (preferably nanofibers ) or particles / aggregates directly on said catalytic layer or dispersed in a liquid carrier by means of dip coating, spraying, slot-die coating,gravure, bar coating, ink-jet printing techniques.

[0055] The membrane group with catalytic coating for membrane electrode assemblies according to the invention is therefore easy to make.

[0056] Preferably, said at least one ion-conducting organic polymer is a proton-conducting polymer, preferably selected from polyanionic polymers.

[0057] According to a particularly preferred embodiment, said proton-conducting polymer is selected from perfluorosulfonic acid (PFSA) ionomers, preferably with equivalent molecular weight between 1,200 and 700 g / mol. In particular, the PFSA may be Nafion or Aquivion.

[0058] Alternatively, said proton-conducting polymer is selected from polystyrene sulfonate (PSS) ionomers, preferably with equivalent molecular weight between 70,000 and 150,000 g / mol.

[0059] In particular, the ion-conducting polymer is selected from polyanionic polymers, preferably consisting of a mixture of perfluorosulfonic acid (PFSA) ionomers and polystyrene sulfonate (PSS) .

[0060] Preferably, the electron-conducting polymer is selected from the group consisting of PEDOT (poly (3, 4- ethylenedioxythiophene ) ) , PPY (polypyrrole) , PANI (polyaniline) , or a mixture thereof.

[0061] The electron-conducting polymer may be present inthe porous layer of conductive material 30 in the form of fibers (preferably nanofibers ) .

[0062] In this case , preferably, said fibers also comprise an ion-conducting polymer, preferably a proton-conducting polymer .

[0063] In particular, said fibers have an average diameter of less than 1 micrometer, and preferably between 100 nanometers and 700 nanometers .

[0064] Alternatively, the electron-conducting polymer may be present in the porous layer of conductive material 30 in the form of particles and / or aggregates .

[0065] In this case , preferably, said particles and / or aggregates also comprise an ion-conducting polymer, preferably a proton-conducting polymer .

[0066] Preferably, said porous layer of conductive material 30 has a thickness between 1 micrometer and 25 micrometers , more preferably between 1 micrometer and 5 micrometers .

[0067] Advantageously, the porous layer of conductive material 30 has an overall porosity suf ficiently high to avoid the introduction of losses related to mass transport , while at the same time exhibiting a compact structure and a reduced average si ze of the interstices between fibers or particles / aggregates in order to ensure the electrical connection of the catalyst particlespresent in the catalytic layer and to maximise contact with the catalytic layer .

[0068] The subj ect of the present invention is an electrolyzer .

[0069] The electrolyzer according to the invention comprises at least one membrane electrode assembly MEA (Membrane Electrode Assembly) .

[0070] As illustrated in Figures 3 and 5 , in turn said at least one membrane electrode assembly comprises :

[0071] - a polymer electrolyte membrane 10 , preferably a proton-conducting polymer electrolyte membrane ,

[0072] - an anode 20 positioned on a first face 11 of the membrane 10 ; and

[0073] - a cathode 200 positioned on a second face 12 of the membrane 10 opposite the first .

[0074] Both the anode and the cathode are each constituted by a catalytic layer 20 , 200 .

[0075] The catalytic layer 20 forming the anode is associated with the membrane 10 in the form of a coating layer .

[0076] Preferably, the catalytic layer 20 forming the anode is based on iridium . In particular, the catalytic layer 20 may be constituted by nanoparticles , e . g . , of IrOx orIrRuOx .

[0077] The electrolyzer comprises a porous transport layer40 , 400 ( PTL, Porous Transport Layer ) for each of the two catalytic layers 20 , 200 of said at least one membrane electrode assembly .

[0078] Each porous transport layer 40 , 400 faces the respective catalytic layer 20 , 200 on the side opposite to the polymer electrolyte membrane 10 .

[0079] According to the invention, the electrolyzer comprises a porous layer of conductive material 30 which is placed to cover the catalytic layer 20 forming said anode so as to be interposed between said catalytic layer 20 and the respective porous transport layer 40 .

[0080] In other words , the conductive material layer 30 is positioned on the opposite side of the membrane 10 with the catalytic layer 20 interposed therein .

[0081] The conductive material layer 30 comprises at least one electron-conducting organic polymer .

[0082] The membrane 10 , the catalytic layer 20 forming the anode , and the porous layer of conductive material 30 form a single body defining a membrane group .

[0083] Preferably, the aforementioned membrane group is a membrane group 1 according to the invention and in particular as previously described .

[0084] The advantages associated with the electrolyzer according to the invention are the same as thosehighlighted for the membrane group 1 according to the invention .

[0085] Preferably, the anodic-side porous transport layer40 comprises a porous main body 41 on which a contact face 411 facing the anodic catalytic layer 20 of the membrane group 1 is identi fied .

[0086] In particular, the aforementioned porous main body41 of the anodic-side porous transport layer 40 may be made of sintered metal , preferably titanium .

[0087] Preferably, said sintered metal is made with particles having an average diameter between 30 and 70 micrometers , more preferably about 50 micrometers . Preferably, the average distance between sintered particles is between 5 micrometers and 60 micrometers , more preferably about 10 micrometers .

[0088] Alternatively, the aforementioned porous main body 41 of the anodic-side porous transport layer 40 may be a non-woven fabric of metallic fibers , preferably titanium . In particular, said metallic fibers have an average diameter between 10 micrometers and 50 micrometers .

[0089] According to the embodiment illustrated in Figures 2 and 3 , the aforementioned porous main body 41 of the anodic-side porous transport layer 40 may come into direct contact with the porous layer of conductive material 30 with its contact face 411 .

[0090] Preferably, according to an alternative embodiment illustrated in Figures 4 and 5 , the anodic-side porous transport layer 40 comprises a porous layer of conductive material 42 which is placed to cover said contact face 411 of the main body 41 so as to be interposed between said main body 41 and said porous layer of conductive material 30 of said membrane group 1 . Operationally, the porous layer of conductive material 42 can improve the contact between the porous transport layer 40 and the porous layer of conductive material 30 covering the catalytic layer 20 . This results , on the one hand, in reduced losses in mass transport and, on the other hand, in increased electrical conductivity .

[0091] According to a preferred embodiment of the invention, the porous layer of conductive material 42 present in the anodic-side porous transport layer 40 comprises at least one electron-conducting organic polymer .

[0092] Preferably, the porous layer of conductive material 42 present in the anodic-side porous transport layer 40 further comprises at least one ion-conducting organic polymer in addition to said at least one electronconducting organic polymer . In other words , preferably, the porous layer of conductive material 42 comprises a mixture of ion-conducting polymer material and electron-conducting polymer material.

[0093] Advantageously, said porous layer of conductive material 42 is integral with the main body 41. In particular, the porous layer of conductive material 42 may be obtained by depositing the polymer materials by electrodeposition, by dip coating technique, or by spray coating technique.

[0094] Preferably, said at least one ion-conducting organic polymer is a proton-conducting polymer, preferably selected from polyanionic polymers.

[0095] According to a particularly preferred embodiment, said proton-conducting polymer is selected from perfluorosulfonic acid (PFSA) ionomers, preferably with equivalent molecular weight between 1,200 and 700 g / mol. In particular, the PFSA may be Nafion or Aquivion.

[0096] Alternatively, said proton-conducting polymer is selected from polystyrene sulfonate (PSS) ionomers, preferably with equivalent molecular weight between 70,000 and 150,000 g / mol.

[0097] In particular, the ion-conducting polymer is selected from polyanionic polymers, preferably consisting of a mixture of perfluorosulfonic acid (PFSA) ionomers and polystyrene sulfonate (PSS) .

[0098] Preferably, the electron-conducting polymer is selected from the group consisting of PEDOT (poly (3, 4-ethylenedioxythiophene ) ) , PPY (polypyrrole ) , PAN I(polyaniline ) , or a mixture thereof .

[0099] The electron-conducting polymer may be present in the porous layer of conductive material 42 in the form of fibers . In this case , preferably, said fibers also comprise an ion-conducting polymer, preferably a protonconducting polymer . In particular, said fibers have an average diameter of less than 1 micrometer, and preferably between 100 nanometers and 700 nanometers .

[0100] Alternatively, the electron-conducting polymer may be present in the porous layer of conductive material 42 in the form of particles and / or aggregates . In this case , preferably, said particles and / or aggregates also comprise an ion-conducting polymer, preferably a protonconducting polymer .

[0101] Preferably, said porous layer of conductive material 42 has a thickness between 1 micrometer and 25 micrometers , more preferably between 5 and 25 micrometers .

[0102] Preferably, the porous layer of conductive material 42 present in the anodic-side porous transport layer 40 has the same chemical composition as the porous layer of conductive material 30 present in the membrane group 1 . Operationally, the mutual contact between materials of the same composition can reduce losses atthe interface related to mass transport .

[0103] The subj ect of the present invention is also a method for producing a membrane group 1 with catalytic coating for membrane electrode assemblies as described above .

[0104] Said method comprises the following operating steps :

[0105] - a ) providing a polymer electrolyte membrane10 , preferably a proton-conducting polymer electrolyte membrane ;

[0106] - b ) depositing on one face 11 , 12 of said membrane 10 a catalytic layer 20 , preferably based on iridium;

[0107] - c ) depositing above said catalytic layer 20 one or more electron-conducting organic polymers so as to form a porous layer of conductive material 30 .

[0108] Preferably, in said step c ) , an ion-conducting organic polymer forming part of said conductive material is also deposited above said catalytic layer 30 .

[0109] Advantageously, said conductive material is deposited in said step c ) in the form of fibers (preferably nanofibers ) or aggregates and / or particles . Preferably, said fibers (preferably nanofibers ) or said aggregates and / or particles consist of a mixture of atleast one electron-conducting polymer (preferably PEDOT ) and at least one ion-conducting polymer (preferably Nation) .

[0110] In particular, said step c ) is carried out by depositing nanofibers :

[0111] - directly onto said catalytic layer ; or

[0112] - dispe rsed in a liquid carrier by means of dip coating, spraying, slot-die coating, gravure , bar coating, ink-j et printing .

[0113] Advantageously, in both cases the nanofibers containing an electron-conducting organic polymer and an ion-conducting organic polymer ( for example respectively PEDOT and Nation) can be made as follows :

[0114] a ) the nanofibers are obtained by spinning from a solution containing both the electron-conducting polymer and the ion-conducting polymer ( for example respectively PEDOT and Nation) ; or

[0115] b ) the nanofibers are obtained by spinning from a solution containing the ion-conducting polymer ( for example Nation) , subsequently introducing the electronconducting polymer ( for example , PEDOT ) into the matrix of said polymer by in situ polymeri zation of a monomer of said polymer ( for example EDOT ) .

[0116] The invention allows to achieve numerous advantages partly already described .

[0117] The invention provides a membrane group with catalytic coating for membrane electrode assemblies which makes it possible to ensure the electrical connectivity of the associated catalytic layer once inserted into a membrane electrode assembly and associated with the respective porous transport layers , thus providing an alternative solution to that of the above-cited known technique .

[0118] Indeed, it has been experimentally veri fied that the presence of the porous layer of polymer-type conductive material , interposed between the catalytic layer and the porous transport layer, reduces the loss of active portions in the catalytic layer as a result of the formation of possible fragments . This signi ficantly reduces the risk of formation of islands and / or disconnected zones in the coated electrode and thus the risk of locally losing the electrical connection with the interface of the porous transport layer and with the remaining part of the catalytic layer .

[0119] The porous layer of polymer-type conductive material thus leads to an increase in conductivity at the interface between the catalytic layer of the membrane group and the porous transport layer, which results in an increase in the electrical connectivity of the catalytically active particles , leading to increasedconductivity at the interface . This makes it possible to reduce the catalyst ( iridium) loading .

[0120] The membrane group with catalytic coating for membrane electrode assemblies according to the invention is also easy to make .

[0121] The invention thus conceived achieves the intended obj ects .

[0122] Obviously, in its practical implementation it may assume also forms and configurations dif ferent from those illustrated above without thereby departing from the present scope of protection .

[0123] Moreover, all details may be replaced with technically equivalent elements and the dimensions , shapes and materials used may be any according to requirements .

Claims

CLAIMS1. A membrane group (1) having a catalytic coating for membrane electrode assemblies comprising:- a polymer electrolyte, preferably proton conductivity polymer electrolyte, membrane (10) on which a first face (11) intended, in use, to define the anode side and a second face (12) , opposite to the first and intended, in use, to define the cathode side in a membrane electrode assembly, are identified;- a catalytic layer (20) , preferably based on iridium, associated with one of said faces (11, 12) of the membrane (10) , preferably being intended in use to act as an anode; characterized in that it comprises a porous conductive material layer (30) which is placed to cover said catalytic layer (20) , and in that said conductive material layer (30) comprises at least one electronconducting organic polymer, wherein the membrane (10) , the catalytic layer (20) , and the porous conductive material layer (30) form a single body .

2. A membrane group (1) according to claim 1, wherein said conductive material layer (30) comprises at least one electron-conducting organic polymer.

3. A membrane group (1) according to claim 2, wherein said at least one ion-conducting organic polymer is aproton-conducting polymer, preferably selected from polyanionic polymers.

4. A membrane group (1) according to claim 3, wherein said proton-conducting polymer is selected from perfluorosulfonic acid (PFSA) ionomers, preferably having an equivalent molecular weight between 1,200 and 700 g / mol .

5. A membrane group (1) according to claim 3, wherein said proton-conducting polymer is selected from polystyrene sulfonate (PSS) ionomers, preferably having an equivalent molecular weight between 70, 000 and 150,000 g / mol .

6. A membrane group (1) according to any one of claims 2 to 5, wherein the ion-conducting polymer is selected from polyanionic polymers, preferably consisting of a mixture of ionomers of perfluorosulfonic acid (PFSA) and polystyrene sulfonate (PSS) .

7. A membrane group (1) according to any one of the preceding claims, wherein the electron-conducting polymer is selected from the group consisting of PEDOT, PPY (polypyrrole) , PANI (polyaniline) or a mixture thereof.

8. A membrane group (1) according to any one of the preceding claims, wherein the electron-conducting polymer is present in the form of fibers, preferably nanofibers.

9. A membrane group (1) according to claim 8, wherein said fibers also comprise an ion-conducting, preferably proton-conducting polymer.

10. A membrane group (1) according to claim 8 or 9, wherein said fibers have an average diameter of less than 1 micrometer, preferably between 100 nanometers and 700 nanometers .

11. A membrane group (1) according to any one of claims 1 to 7, wherein the electron-conducting polymer is present in particle and / or aggregate form.

12. A membrane group (1) according to claim 11, wherein said particles and / or aggregates also comprise an ionconducting, preferably proton-conducting polymer.

13. A membrane group (1) according to any one of the preceding claims, wherein said conductive material layer (30) has a thickness between 1 micrometer and 25 micrometers, more preferably between 1 micrometer and 5 micrometers .

14. An electrolyzer comprising at least one membrane electrode assembly, which in turn comprises: a polymer electrolyte, preferably proton-conducting polymer electrolyte, membrane (10) ;-an anode (20) positioned at a first face (11) of the membrane (10) ; a cathode (200) positioned at a second face (12) of themembrane (10) opposite to the first; wherein said anode and said cathode both consist of a catalytic layer (20; 200) , the catalytic layer (20) forming the anode being associated with the membrane (10) in the form of a coating layer, and wherein said electrolyzer comprises a porous transport layer (40; 400) for each of the two catalytic layers of said at least one membrane electrode assembly, each porous transport layer (40; 400) facing the respective catalytic layer (20; 200) on the opposite side with respect to the polymer electrolyte membrane (10) , characterized in that said electrolyzer comprises a porous conductive material layer (30) which is placed to cover the catalytic layer (20) forming said anode to be interposed between said catalytic layer (20) and the respective porous transport layer (40) , and in that said conductive material layer (30) comprises at least one electron-conducting organic polymer, wherein said membrane (10) , the catalytic layer (20) forming the anode and said porous conductive material layer (30) form a single body defining a membrane group.

15. An electrolyzer according to claim 14, wherein said membrane group is a membrane group (1) according to any one of claims 1 to 13.

16. An electrolyzer according to claim 14 or 15, whereinthe porous, anode-side transport layer comprises a porous main body (41) on which a contact face (411) facing the anode catalytic layer is identified.

17. An electrolyzer according to claim 16, wherein the porous, anode-side transport layer comprises a porous conductive material layer (42) which is placed to cover said contact face (411) of the main body (41) to be interposed between said main body (41) and said porous conductive material layer (30) of said membrane.

18. An electrolyzer according to claim 17, wherein said conductive material layer (42) comprises at least one electron-conducting organic polymer.

19. An electrolyzer according to claim 18, wherein said conductive material layer (42) further comprises at least one ion-conducting organic polymer.

20. A method of producing a membrane group (1) having a catalytic coating for membrane electrode assemblies according to any one of claims 1 to 13, comprising the following operating steps:- a) providing a polymer electrolyte, preferably protonconducting polymer electrolyte, membrane (10) ;- b) depositing a catalytic layer (20) , preferably based on iridium, on a face (11, 12) of said membrane (10) ;- c) depositing, above said catalytic layer (20) , one or more electron-conducting organic polymers so as to form aporous conductive material layer (30) .

21. A method according to claim 20, wherein in said step c) an ion-conducting organic polymer forming part of said conductive material is also deposited above said catalytic layer (20) .

22. A method according to claim 21, wherein said conductive material is deposited in said step c) in the form of nanofibers or aggregates and / or particles, preferably said nanofibers or said aggregates and / or particles consisting of a mixture of at least one electron-conducting organic polymer, preferably PEDOT, and at least one ion-conducting organic polymer, preferably Nation.

23. A method according to claim 22, wherein said step c) is carried out by depositing said nanofibers:- directly onto said catalytic layer (20) ; or dispersed in a liquid carrier by a dip coating, spraying, slot-die coating, gravure, bar coating, ink-jet printing technique.

Images