New membrane-electrode assembly (MEA) and its manufacturing method

Abstract

The present invention relates to a novel membrane-electrode assembly (MEA), a method for producing the same, and a fuel cell using the MEA.

Description

[Technical Field]

[0001] The present invention relates to a novel membrane-electrode assembly (MEA) and its manufacturing method, as well as a fuel cell comprising said MEA, which exhibits improved performance by reducing losses associated with charge and mass transport phenomena. [Background technology]

[0002] The heart of a modern polymer membrane fuel cell (FC) is the so-called "membrane-electrode assembly (MEA)". The MEA is a two-dimensional, multi-layer system that contains all the basic components required to make the FC work. These components include: 1. An ion exchange membrane suitable for conducting the ionic species involved in the operation of a particular FC. Different types of FCs require membranes that conduct different ionic species. For example, a "proton exchange membrane fuel cell" (PEMFC) uses HO + Anion exchange membrane fuel cells (AEMFCs) contain a membrane capable of conducting ions instead of OH. - It includes a membrane capable of conducting ions. 2. The ion exchange membrane is coated on both sides with an "electrode catalyst layer." 3. Each electrocatalyst layer is then covered with a "gas diffusion electrode", and these two electrocatalyst layers ensure the following functions: (i) they help the reactants required for FC operation to reach the electrocatalyst layers, (ii) they remove from the MEA the products resulting from the electrochemical processes required for FC operation, and (iii) they put the electrocatalyst layers into electrical contact with the external circuit.

[0003] The electrocatalyst layer is where the oxidation or reduction processes necessary for the overall operation of the FC take place. Within the electrocatalyst layer, there are "active sites": 1. Sites in ionic contact with the electrolyte membrane of the FC. For example, in the case of a PEMFC, (i) at the anode, these sites are in ionic contact with the electrolyte membrane of the FC. + ions toward the membrane; and simultaneously (ii) at the cathode, HO from the membrane.+ Accepts ions. 2. The parts exposed to the reactants used to feed the FC, for example in the case of a PEMFC (i) at the anode, exposed to hydrogen; and simultaneously (ii) at the cathode, exposed to oxygen. 3. The part that is in electrical contact with the external circuit. For example, in the case of a PEMFC, (i) the anode sends electrons out of the system to the external circuit; and (ii) the cathode absorbs electrons coming in from the external circuit.

[0004] In order for the "active sites" contained in the electrode catalyst layer to come into ionic contact with the electrolyte membrane of the FC, appropriate permeation pathways must be formed for the transport of ions of interest. These latter ions participate as reactants or products in the electrochemical processes occurring at the electrodes of the FC. If these ions do not reach or are not removed from the "active sites," the electrochemical processes necessary for the overall operation of the FC will not occur, and the device will not generate current.

[0005] To create permeation pathways for the transport of target ions, a certain amount of ion-exchange polymer is introduced into the electrocatalyst layer, which can readily conduct the same ions that migrate through the electrolyte membrane. The optimal amount of such polymer depends on various factors, including the morphology of the electrocatalyst. On the other hand, if the electrocatalyst layer does not contain enough ion-exchange polymer, many of the "active sites" contained in the electrocatalyst layer cannot be reached by ionic species and therefore cannot function. On the other hand, if the amount of ion-exchange polymer is excessive, (i) the ion-exchange polymer will coat the "active sites" and inhibit their function, and (ii) it will electrically insulate the individual particles into which the electrocatalyst is divided, inhibiting the transport of electrons between the "active sites" and the external circuit.

[0006] To facilitate the transfer of ions of interest between the electrocatalyst layer and the membrane, and vice versa, it is essential that the interface between these two components is smooth and uniform, ensuring that the various steps in MEA fabrication do not introduce bubbles or other discontinuities that would impede the transfer of ions between the membrane and the ion-exchange polymer contained in the electrocatalyst layer.

[0007] For each electrocatalyst layer to function optimally, it is necessary to maximize the rate at which a specific redox process occurs at the electrode. For example, in a PEMFC, (i) at the anode, this process is the electrooxidation of hydrogen, and (ii) at the cathode, this process is the reduction of oxygen. The "active sites" within each electrocatalyst layer are provided by an appropriate electrocatalyst material. The chemical composition and structure of these "active sites" are appropriately adjusted to accelerate the desired redox process. For example, in a PEMFC, the "active sites" are typically platinum-based and exist in the form of nanoparticles, typically with diameters between 2 and 5 nm.

[0008] However, while the specific rate at which a particular redox process occurs is fundamental, optimal operation of the electrocatalytic layer also requires the following: 1. The "active site" must be able to accommodate all the reactants necessary to carry out the desired redox process. 2. The "active site" must be able to excrete all of the products of the desired redox process. 3. The "active site" must be in good electrical contact with the external circuit and be able to exchange all the electrons required for the desired redox process with the external circuit.

[0009] Typically, the exchange of electrons between the "active sites" of each electrocatalyst layer and the external circuit is very simple because the electrocatalyst materials that provide these "active sites" are made of highly conductive components, such as platinum and carbon nanoparticles.

[0010] On the other hand, the transport of reactants and products in the electrode catalyst layer involves ionic species with much larger masses than electrons (e.g., HO + ), or neutral species with much greater mass than electrons (e.g., H2, O2, HO). The main transport problem occurs at the FC electrodes, where recombination of ionic species occurs. This is because the release of the reaction products that power the system occurs at these electrodes. In FCs operating at low temperatures, such as conventional PEMFCs and AEMFCs, this product consists of liquid water. In PEMFCs, the electrode where water is generated is the cathode, and in AEMFCs, the electrode where water is generated is the anode. If not properly removed, the latter can cause a flooding phenomenon that "suffocates" the "active sites," hindering operation. This is primarily because gaseous reactants, such as hydrogen and oxygen, have difficulty reaching the "active sites" by diffusion when they are covered by liquid water. This problem is particularly problematic when FCs generate high currents, due to the large amount of liquid water released.

[0011] To facilitate the removal of liquid water, the "active sites" must be well exposed to the external environment. To achieve this goal, it is necessary to identify the morphology of the electrocatalyst that provides these "active sites," for example, by ensuring that these "active sites" are characterized as being highly "accessible" to reactants and products.

[0012] Electrocatalyst materials commonly employed in the prior art have many limitations. In particular, prior art electrocatalyst materials are obtained by coating existing supports (typically carbonaceous materials such as carbon black) with platinum-based nanoparticles coated with active sites that promote the desired process. While this approach results in high-performance electrocatalysts, it typically suffers from poor durability due to the very weak interaction between the support and the platinum nanoparticles. As a result, during electrocatalytic operation, the platinum nanoparticles undergo the following phenomena: (i) exfoliation, (ii) agglomeration, and (iii) the release of other elements (typically first-row transition metals such as Ni and Co) that may be present to enhance the performance of the "active sites." Ultimately, these decomposition phenomena significantly reduce the activity of the electrocatalyst to promote the desired process.

[0013] Numerous approaches exist for obtaining electrocatalyst materials with improved performance and durability. Specifically, WO 2017 / 055981 describes a preparation approach that results in carbonitride-based electrocatalysts with a "core-shell" morphology, which establishes very strong interactions between the "active sites" and the support. However, the morphology of carbonitride-based electrocatalysts with a "core-shell" morphology is very different from that of prior art electrocatalysts. In the latter, various particles of the support material are bound by a "shell" of carbonitride, resulting in larger electrocatalyst particles.

[0014] As a result, the surface of the electrocatalyst layer is typically significantly rougher than that of electrocatalyst layers containing prior art electrocatalysts. This roughness prevents the formation of a continuous and homogeneous interface between the ion-exchange membrane and the electrocatalyst layer, hindering the transport of ionic species necessary for FC operation.

[0015] Furthermore, the active sites of the electrocatalyst described in WO 2017 / 055981 are not "coated from the outside" on a support as in prior art electrocatalyst materials, but are "grown from the inside" within the carbonitride "shell" and are therefore not necessarily fully exposed to the external environment, so that many "active sites" are either practically unused (inaccessible to the reactants of the intended process) or located at the bottom of the very narrow and tortuous pores of the carbonitride "shell" (thus, these difficulties in transporting reactants and products significantly reduce the efficiency of the electrocatalyst).

[0016] U.S. Patent Application Publication No. 2005 / 112448 describes ion-exchange polymers used as adhesion layers to minimize electrode delamination from the membrane, which can actually reduce the efficiency of the battery.

[0017] US Patent Application Publication No. 2010 / 068592 describes ion exchange polymers that are used to solve compatibility issues between hydrocarbon-based ion exchange polymer membranes and electrodes optimized for DMFCs. Summary of the Invention [Problem to be solved by the invention]

[0018] The object of the present invention is to overcome the above drawbacks and to provide a membrane-electrode assembly (MEA) end product with improved performance. [Means for solving the problem]

[0019] The inventive approach therefore allows for (i) improved intercompatibility between the various layers that make up the MEA by facilitating the movement of ionic species, and (ii) improved accessibility of the electrocatalytic active sites to the reactants and products of the electrochemical processes required for the operation of the MEA.

[0020] Therefore, in a first aspect, the present invention relates to a membrane-electrode assembly (MEA) as set forth in claim 1, with preferred features of the method being recited in the dependent claims.

[0021] More specifically, the membrane-electrode assembly comprises: - an anode and a cathode facing each other; an ion exchange membrane disposed between the anode and the cathode; - an electrode catalyst coating layer applied to both sides of the ion exchange membrane; - an ion exchange polymer layer disposed between the membrane and at least one of the electrocatalyst layers; wherein the electrocatalyst layer comprises micropores having an average diameter between 0.001 and 50 micrometers, preferably between 0.01 and 1 micrometer, and wherein the electrocatalyst layer comprises electrocatalyst particles having an average diameter between 0.01 and 10 micrometers, preferably between 0.03 and 0.3 micrometers.

[0022] The membrane-electrode assembly (MEA) of the present invention can simultaneously satisfy two conditions: (i) establishing good electrical contact between the active sites of the electrocatalyst and an external electrical circuit, and (ii) having good ionic contact between the active sites of the electrocatalyst and the ion-conducting membrane separating the two electrodes.

[0023] Advantageously, the ion exchange polymer layer improves the transport of ionic species between the electrocatalyst layer and the ion exchange membrane, thereby enabling the "establishment of an ionic bridge" between the membrane and the electrocatalyst layer.

[0024] Advantageously, by incorporating a suitable "pore-forming agent" into the electrocatalyst layer, cavities can be formed in the electrocatalyst layer, which (i) facilitates the distribution of reactants within the electrocatalyst layer and (ii) facilitates the removal of products from the electrocatalyst layer.

[0025] Advantageously, electrocatalyst grinding in the presence of a suitable "grinding agent" can be used to reduce the particle size of the electrocatalyst, facilitating the exposure of active sites, thereby promoting reactant and product transport phenomena and the formation of a continuous, homogeneous interface between the ion exchange membrane and the electrocatalyst layer.

[0026] In manufacturing an MEA, various embodiments of the present invention can be used individually or simultaneously.

[0027] According to its second aspect, the present invention provides a method for producing a medicament for a medicament comprising: (a) providing a dispersion of an ion exchange polymer in a protic polar solvent or in a solution comprising two or more protic polar solvents; (b) applying the dispersion onto an ion exchange membrane or onto at least one electrocatalytic layer applied onto the membrane by either (i) direct application onto the membrane or onto the at least one electrocatalytic layer, or (ii) application onto an inert substrate followed by transfer onto the membrane or onto the at least one electrocatalytic layer to form a membrane-polymer layer system or an electrocatalytic layer-polymer layer system; (c) removing the solvent, preferably by evaporation, evaporation under reduced pressure, or drying; (d) optionally, applying pressure and / or treating the membrane-polymer layer system or the electrocatalyst layer-polymer layer system with at least one acidic or basic aqueous solution; The present invention also relates to a method for producing the above-mentioned membrane-electrode assembly, comprising:

[0028] When the electrocatalyst layer comprises micropores, the method for producing an MEA according to the present invention further comprises the steps of introducing at least one pore-forming agent into the electrocatalyst layer and subsequently removing said at least one pore-forming agent from the electrocatalyst layer.

[0029] When the electrocatalyst layer comprises electrocatalyst particles having an average diameter between 0.01 micrometers and 10 micrometers, preferably between 0.03 micrometers and 0.3 micrometers, the method for manufacturing an MEA of the present invention further comprises the following steps: - grinding the electrocatalyst in the presence of at least one grinding agent; and - removing said at least one abrasive from said electrocatalyst.

[0030] According to a third aspect, the present invention relates to a membrane-electrode assembly obtainable from the method according to the invention described above.

[0031] According to a fourth aspect, the present invention relates to a fuel cell comprising a membrane-electrode assembly as described above.

[0032] Further features and advantages of the present invention will become more apparent from the following description of some preferred embodiments, taken in conjunction with the accompanying drawings, which are provided below for illustrative and non-limiting purposes. [Brief explanation of the drawings]

[0033] [Figure 1] The polarization curves of MEA1 and MEA2 are shown. Experimental measurement conditions: anode / cell / cathode = 84 / 85 / 84°C. Pure hydrogen is supplied to the anode at a flow rate of 800 sccm. Pure oxygen is supplied to the cathode at a flow rate of 500 sccm or air at a flow rate of 1700 sccm. The relative humidity of all gaseous reactants is equal to 100%. The back pressure of the gaseous reactants is equal to 0.45 MPa. [Figure 2] The polarization curves of MEA3 and MEA4 are shown. Experimental measurement conditions: anode / cell / cathode = 84 / 85 / 84°C. Pure hydrogen is supplied to the anode at a flow rate of 800 sccm. Pure oxygen is supplied to the cathode at a flow rate of 500 sccm or air at a flow rate of 1700 sccm. The relative humidity of all gaseous reactants is equal to 100%. The back pressure of the gaseous reactants is equal to 0.10 MPa. [Figure 3]Photographs of RRDE chips coated with a deposited and dried layer containing EC PtNi1, which is provided with the "pristine PtNi1" mixture (a) or the "treated PtNi1" mixture according to the invention (b). [Figure 4] Figure 1 shows the RDE profile of EC PtNi1, which is prepared using the "pristine PtNi1" mixture or the "treated PtNi1" mixture according to the present invention. [Figure 5] Photographs of RRDE chips coated with a deposited and dried layer containing EC PtCu1, which is provided with the "initial PtCu1" mixture (a) or the "treated PtCu1" mixture according to the invention (b). [Figure 6] 1 shows the RDE profile of EC PtCu1, which is prepared using the "initial PtCu1" mixture or the "treated PtCu1" mixture according to the invention. [Figure 7] Polarization curves of MEA5 and MEA6. Experimental measurement conditions: anode / cell / cathode = 84 / 85 / 84°C. Pure hydrogen is supplied to the anode at a flow rate of 800 sccm. Pure oxygen is supplied to the cathode at a flow rate of 500 sccm or air at a flow rate of 1700 sccm. The relative humidity of all gaseous reactants is equal to 100%. The back pressure of the gaseous reactants is equal to 0.45 MPa. DETAILED DESCRIPTION OF THE INVENTION

[0034] (Definition explanation) Unless otherwise defined, all technical terms, notations, and other scientific terms used herein are intended to have the meanings commonly understood by those skilled in the art to which this application pertains. In some cases, for clarity and / or ease of reference, terms having commonly understood meanings are defined herein. Therefore, the inclusion of such definitions herein should not be interpreted as representing a substantial deviation from the common understanding in the art.

[0035] As used herein, the terms "approximately" and "about" refer to the range of experimental error inherent in performing experimental measurements.

[0036] "Ambient temperature" refers to a temperature between 15°C and 25°C.

[0037] The terms "comprising," "having," "including," and "containing" should be construed as open-ended terms (i.e., meaning "including, but not limited to") and should be considered to refer to terms such as "consist essentially of," "consisting essentially of," "consist of," or "consisting of."

[0038] The terms "consist essentially of" and "consisting essentially of" should be construed as semi-closed-ended terms, meaning that no other components that affect the novel characteristics of the invention are included (and therefore, optional excipients may be included).

[0039] Additionally, the terms "consist of" or "consisting of" are to be construed as closed-ended terms.

[0040] In a first aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: - an anode and a cathode facing each other; an ion exchange membrane disposed between the anode and the cathode; - an electrode catalyst coating layer applied to both sides of the ion exchange membrane; - an ion exchange polymer layer disposed between the membrane and at least one of the electrocatalyst layers; wherein the electrocatalyst layer comprises micropores having an average diameter between 0.001 and 50 micrometers, preferably between 0.01 and 1 micrometer, and wherein the electrocatalyst layer comprises electrocatalyst particles having an average diameter between 0.01 and 10 micrometers, preferably between 0.03 and 0.3 micrometer.

[0041] One aspect of the present invention is the introduction of an ion-exchange polymer layer (referred to as "StratIon") between the ion-exchange membrane (referred to as "Membr") contained in the MEA and at least one of the adjacent electrode catalyst layers. The introduction of such StratIon allows for good ionic conduction between the Membr and the active sites contained in the electrode catalyst layer.

[0042] The ion exchange polymer is selected from the group consisting of ionomers suitable for exchanging (i) cations, (ii) anions, or (iii) both anions and cations.

[0043] Examples of cationic ionomers that can be used in the present invention are perfluorosulfonated ionomers (PFSA ionomers), such as Nafion, Aquivion, or Hyflon-Ion.

[0044] However, cation exchange groups (e.g., -SO3 - , -ClO3 - It is also possible to use other polymers functionalized with -N(CH3)3, etc. It is also possible to use ionomers suitable for the exchange of anions, such as -N(CH3)3 + , pyridine, or similar groups. Finally, it is also possible to use ionomers which simultaneously have groups capable of exchanging cations and groups capable of exchanging anions.

[0045] According to a preferred embodiment, the StratIon film thickness is between 2 and 1000 micrometers, preferably between 2 and 50 micrometers.

[0046] In a further preferred embodiment of the present invention, the electrocatalyst layer comprises an electrocatalyst, preferably a carbonitride-based electrocatalyst having a "core-shell" morphology, or an electrocatalyst comprising graphene oxide, graphene nitride, graphene, or graphene functionalized with -COOH and / or -OH groups.

[0047] Examples of electrocatalysts that can be used in the present invention are carbonitride-based electrocatalysts with a "core-shell" morphology, such as those described in WO 2017 / 055981. Examples of catalysts comprising graphene oxide, graphene nitride, graphene, or graphene functionalized with -COOH and / or -OH groups are those described in WO 2018 / 122368.

[0048] Thus, StratIon can be obtained according to one of the following approaches: (i) direct application to a membrane or electrocatalytic layer, (ii) "ex-situ" preparation followed by transfer to a membrane, and (iii) "ex-situ" preparation followed by transfer to an electrocatalytic layer.

[0049] According to a second aspect, the present invention relates to a method for producing the membrane-electrode assembly described above, said method comprising the steps of: (a) providing a dispersion of an ion exchange polymer in a protic polar solvent or in a solution comprising two or more protic polar solvents; (b) depositing said dispersion onto an ion exchange membrane or at least one electrocatalytic layer applied thereto by (i) direct application (e.g., manual brushing or "ink jet" printing) onto said membrane or said at least one electrocatalytic layer, or (ii) application onto an inert substrate (e.g., a Teflon™ sheet) followed by transfer onto said membrane or said at least one electrocatalytic layer to form a membrane-polymer layer system or an electrocatalytic layer-polymer layer system; (c) removing the solvent, preferably by evaporation, evaporation under reduced pressure, or drying; (d) optionally, applying pressure and / or treating the membrane-polymer layer system or the electrocatalyst layer-polymer layer system with at least one acidic or basic aqueous solution; Includes:

[0050] The polar protic solvent that can be used in step (a) of the method of the present invention is selected from C1-C4 alcohols, water, or carboxylic acids. C1-C4 alcohols are preferred. A solution containing two or more solvents (e.g., water and isopropyl alcohol) can also be used.

[0051] In Example 1 below, MEA1 was fabricated by incorporating StratIon between the ion exchange membrane and the cathode electrode catalyst layer. The performance of MEA1 was observed to be significantly superior to that of MEA2 (which is identical to MEA1 except that it does not contain the StratIon layer). Based on these results, the conclusion is that the introduction of an ion exchange polymer layer between the electrode catalyst layer and the ion exchange membrane significantly enhances the performance of the MEA due to improved ionic contact between the membrane and the active sites, resulting in a clear improvement.

[0052] A further aspect of the present invention is the formation of micropores in the electrocatalytic layers of the MEAs having an average diameter between 0.001 and 50 micrometers, preferably between 0.01 and 1 micrometer, by incorporating a suitable "pore former" into the ink formulation used to obtain the electrocatalytic layers.

[0053] The pore-forming agent can be removed from the electrocatalyst layer after appropriate treatment, leaving behind cavities that increase the interfacial area between the electrocatalyst material and the external environment, through which reactants of processes facilitated by the electrocatalyst material itself can be delivered.

[0054] A method for producing an MEA according to the present invention may comprise the steps of introducing at least one pore-forming agent into an electrocatalyst layer and subsequently removing said at least one pore-forming agent from the electrocatalyst layer.

[0055] In a preferred embodiment, the ratio between the volume of pore former introduced into the electrocatalytic layer and the volume of electrocatalytic material contained in said layer varies between 10 and 0.01, preferably between 1 and 0.1.

[0056] Typical examples of pore-forming agents that can be used in the present invention are solids that are readily water-soluble (e.g., alkali metal or alkaline earth metal halides such as LiBr, NaI, CaCl) or solids that are readily soluble in weakly acidic aqueous solutions (metal oxides such as ZnO, TiO, SiO, or inorganic salts of alkali metals or alkaline earth metals such as, for example, carbonates, CaCO, sulfates, nitrates, phosphates), or mixtures thereof.

[0057] In a preferred embodiment, the pore former consists of particles having an average diameter between 10,000 nm and 2 nm, preferably between 200 nm and 20 nm.

[0058] The pore former may be incorporated into the electrocatalytic layer by simply dispersing the components in the ink used to obtain the same electrocatalytic layer. It is also possible to combine (e.g., mill) the various components of the pore former before incorporating them into the ink.

[0059] The ink containing the pore-former is processed in the same way as other inks suitable for the production of electrocatalytic layers. Thus, the ink may be applied onto the electrodes of an MEA ("catalyst coated substrate" (CCS) procedure), or onto an ion-exchange membrane ("catalyst coated membrane" (CCM) procedure, e.g., by decal). At this point, once the liquid phase of the ink has been removed (usually by evaporation), the pore-former must be removed from the resulting electrocatalytic layer.

[0060] This removal is generally achieved by: (i) washing with an acidic or basic aqueous solution, optionally in the presence of at least one gas bubbled through the solution; (ii) vacuum sublimation; (iii) ultrasonic treatment; (iv) decantation; (v) filtration; (vi) addition of a suitable additive followed by flotation; (vii) treatment with a non-polar organic solvent (such as toluene, hexane, heptane, benzene, or mixtures thereof); (viii) treatment with an aprotic polar solvent (such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, or mixtures thereof); or (ix) treatment with an aldehyde, ketone, carboxylic acid, amine, or mixtures thereof.

[0061] In Example 2 below, an ink containing ZnO is prepared. This last component acts as a pore-forming agent. The electrocatalyst layer containing this agent is then repeatedly treated with an aqueous acid solution to (i) remove the pore-forming agent itself and (ii) remove the ZnO resulting from the dissolution of the pore-forming agent. 2+ The MEA prepared in Example 2 also includes an ion-exchange polymer layer between the ion-exchange membrane contained in each MEA and at least one of the electrode catalyst layers in contact with the ion-exchange membrane.

[0062] At the end of this process for fabricating MEAs, it is noted that the performance of MEA3 (one of the electrocatalytic layers contains a pore-former) is much better than that of MEA4 (no pore-former was added). Thus, it is concluded that the addition of an appropriate pore-former has a clear improving effect on the performance of MEAs.

[0063] A further aspect of the present invention is to carry out extensive milling of the electrocatalyst material by combining the electrocatalyst material itself with a suitable "milling agent" to obtain an electrocatalyst layer comprising electrocatalyst particles having an average diameter between 0.01 and 10 micrometers, preferably between 0.03 and 0.3 micrometers.

[0064] The grinding agent typically consists of a powder of a hard but brittle material, such as a metal oxide, typical examples of which are systems such as ZnO, TiO2, and SiO2.

[0065] It is also possible to use inorganic salts of alkali metals or alkaline earth metals, such as alkali metal or alkaline earth metal halides (LiBr, NaI, CaCl2), carbonates, sulfates, nitrates, phosphates, or mixtures thereof.

[0066] This grinding procedure in the presence of a grinding agent primarily serves to reduce the particle size of the electrocatalyst, thus increasing the surface area of ​​the electrocatalyst and at the same time improving the accessibility of its active sites.

[0067] A method for producing an MEA according to the present invention may comprise grinding an electrocatalyst in the presence of at least one grinding agent, and subsequently removing said at least one grinding agent from said electrocatalyst.

[0068] In a preferred embodiment, the ratio between the volume of the grinding agent and the total volume of the material to be ground (the latter comprising the electrocatalyst and optionally further components such as carbonaceous materials like carbon black) is between 10 and 0.01, preferably between 1 and 0.1.

[0069] The particle size of the grinding agent may vary in the range between 1 mm and 2 nm, preferably between 100 nm and 10 nm.

[0070] In a preferred embodiment of the grinding step, the duration of the step in the presence of at least one grinding agent varies from 20 minutes to 400 hours, preferably from 30 minutes to 1 hour.

[0071] Optionally, the grinding process can be carried out in the presence of a grinding agent by adding a suitable liquid to the grinding mixture. Such liquids include water, alcohols, aldehydes, ketones, ethers, esters, hydrocarbons, amines, amides, or mixtures thereof. The liquid can be added at the beginning of the process or at any time during grinding. Liquids of different compositions can also be added at different times during the grinding process.

[0072] The grinding agent may be composed of one or more different components, each of which may be added to the grinding mixture at any point during the grinding process.

[0073] The grinding step in the presence of a grinding agent may be carried out at a temperature between -270°C and 1700°C, preferably between -195°C and 200°C, more preferably at room temperature. In the grinding step in the presence of a grinding agent, the temperature can be adjusted as desired.

[0074] The grinding process in the presence of the grinding agent can be carried out in the presence of an electric and / or magnetic field of desired strength and time course, as desired.

[0075] At the end of the grinding process in the presence of a grinding agent, said grinding agent can be removed from the system.

[0076] This removal can be accomplished using one or more of the following processes: (i) washing with a suitable liquid phase (e.g., an acidic or basic aqueous solution), optionally in the presence of at least one gas bubbled through the liquid phase; (ii) vacuum sublimation; (iii) ultrasonic treatment; (iv) decantation; (vi) filtration; (vi) addition of a suitable additive and subsequent flotation; (vii) treatment with a non-polar organic solvent (such as toluene, hexane, heptane, benzene, or mixtures thereof); (viii) treatment with an aprotic polar solvent (such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, or mixtures thereof); (ix) treatment with an aldehyde, ketone, carboxylic acid, amine, or mixtures thereof.

[0077] In the following Examples 3 and 4, a mixture was prepared using ZnO nanoparticles with a diameter equal to 50 nm as a grinding agent. This mixture was homogeneous and stable, producing a highly uniform layer on the RRDE chip disk. These layers were much more uniform than those obtained without the addition of ZnO. This chip was used for CV-TF-RRDE (cyclic voltammetry, thin film, rotating ring-disk electrode) studies, which were performed in an acidic environment, which removed the ZnO nanoparticles contained in the mixture deposited on the RRDE chip. The CV-TF-RRDE studies demonstrated that the treatments described in Examples 3 and 4 according to the present invention did not alter the active sites of the electrocatalyst, while at the same time improving the accessibility of these active sites to reactants or products, resulting in a clear improvement.

[0078] In the following Example 5, a mixture was prepared using ZnO nanoparticles with a diameter equal to 50 nm as a grinding agent. This mixture was homogeneous and stable, making it possible to produce a very uniform electrocatalytic layer. The latter was then repeatedly treated with an acidic aqueous solution to remove the grinding agent and the by-products resulting from its dissolution (especially ZnO). 2+ ) was removed. It should be noted that in this specific Example 5, ZnO simultaneously serves two roles: (i) a "grinding agent" that reduces the particle size of the electrocatalyst particles introduced into the electrocatalyst layer, and (ii) a "pore former" that, when removed, leaves voids within the electrocatalyst layer to improve reactant distribution and allow for removal of the products of the target process promoted by the electrocatalyst (in this case, the oxygen reduction reaction leading to water production).

[0079] The aforementioned aspects of the invention, i.e., (i) the introduction of an ion exchange polymer layer between the membrane and at least one electrocatalyst layer, (ii) the formation of micropores in the electrocatalyst layer, or (iii) the reduction of the particle size of the electrocatalyst, can be used individually or simultaneously in the fabrication of an MEA.

[0080] The methods for manufacturing MEAs according to the present invention may be used individually or in conjunction with one another.

[0081] According to a third aspect, the present invention relates to a membrane-electrode assembly obtainable by the method according to the invention as described above.

[0082] According to a fourth aspect, the present invention relates to a fuel cell comprising a membrane-electrode assembly as described above. [Example]

[0083] Example 1 This example relates to an EC designated "PtNi2." EC PtNi2 was prepared as described in WO 2017 / 055981 and WO 2018 / 122368. PtNi2 contains 6.93 wt% Pt and 1.43 wt% Ni. The fabrication of the MEA containing EC PtNi2 is carried out as follows.

[0084] A total of 250 microliters of a 5 wt% Nafion dispersion in alcohol (hereafter referred to as "5 wt% Nafion alcohol dispersion") was spread onto a Teflon™ sheet to form a square with an area equal to 5 square centimeters. The Teflon™ sheet was then dried at 90°C to remove the solvent, forming a Nafion layer deposited on the Teflon layer. This layer was referred to as "StratIon."

[0085] The StratIon layer is transferred by decal onto a dry proton exchange membrane (called "Membr") with a thickness of 15 microns and a proton exchange capacity equal to 2.94 milliequivalents per gram. The transfer is carried out by a hot pressing procedure, in which the system is held at 146°C for 5 minutes and a pressure of 3.45 MPa is employed. The resulting product is called "Membr+StratIon".

[0086] The Membr+StratIon is subjected to the following activation procedure: (i) wash with bidistilled water at 80° C. for 1 hour, (ii) wash with 3% H2O2 at 80° C. for 1 hour, (iii) wash twice with 1 M H2SO4 at 80° C. for 1 hour, (iv) wash once with bidistilled water at 80° C. for 1 hour. The Membr+StratIon is then dried with a dry air stream for 24 hours before use in MEA fabrication.

[0087] 20 mg of PtNi2 and 10 mg of Vulcan XC-72R carbon black were combined and vigorously ground. The resulting mixture was placed in a vial, and 200 microliters of double-distilled water was added, followed by 1 milliliter of isopropyl alcohol. The resulting suspension was vigorously sonicated using a tip sonicator. 366 microliters of a 5 wt% Nafion alcohol dispersion was added to the suspension. The resulting suspension was vigorously sonicated using a tip sonicator. The resulting product was a suspension designated "SospCat."

[0088] To 20 mg of standard EC (containing 20 wt. % platinum, designated "Pt / C Standard 2") in a vial, 200 microliters of double-distilled water is added, followed by 1 milliliter of isopropyl alcohol. The resulting suspension is vigorously sonicated using a tip sonicator. Next, 206 microliters of a 5 wt. % Nafion alcohol dispersion is added to the suspension. The suspension is vigorously sonicated using a tip sonicator, and the resulting product is a suspension designated "SospAn."

[0089] An aliquot of SospCat is deposited onto the microporous layer of a 2 x 2 cm Teflon-coated carbon paper electrode such that the total platinum loading on the electrode is 0.05 milligrams of platinum per square centimeter of electrode. To achieve this, the weight of the solids deposited on the electrode (obtained by drying the SospCat suspension) should be equal to 6.78 mg. The resulting electrode is referred to as the "PtNi2 cathode."

[0090] An aliquot of SospAn is deposited onto the microporous layer of a 2 x 2 cm Teflon-coated carbon paper electrode so that the total platinum loading on the electrode is 0.4 milligrams of platinum per square centimeter of electrode. To achieve this, the weight of the solids deposited on the electrode (obtained by drying the SospAn suspension) should be equal to 11.84 mg. The resulting electrode is referred to as the "Pt / C Reference 2 Anode."

[0091] Two Pt / C reference 2 anodes and a PtNi2 cathode are hot-pressed onto the Membrane+StratIon. A layer containing EC PtNi2 deposited on the PtNi2 cathode electrode is placed in direct contact with the StratIon layer. A layer containing EC Pt / C reference 2 deposited on the Pt / C reference 2 anode electrode is placed in direct contact with the other side of the Membrane+StratIon. The hot-pressing procedure is carried out at a temperature of 146°C and a pressure of 762 MPa (these parameters are maintained for 5 minutes). At the end of this process, an MEA designated MEA1 is obtained.

[0092] A second reference MEA, designated MEA 2, is prepared, which is identical to MEA 1 with the only difference being that MEA 2 does not include the StratIon layer.

[0093] MEA1 and MEA2 are tested in single cells, and the corresponding polarization curves are shown in Figure 1.

[0094] It is noteworthy that the introduction of a StratIon layer between the Membr and the electrocatalytic layer (comprising EC PtNi2 and deposited on a PtNi2 cathode) significantly improves the performance of the MEA.

[0095] Example 2 This example refers to the same EC used in Example 1. The manufacture of an MEA containing the EC PtNi2 is carried out as follows.

[0096] A total of 250 microliters of a 5 wt% Nafion alcohol dispersion is spread onto a Teflon™ sheet to form a square with an area equal to 5 square centimeters. This is then dried at 90°C to remove the solvent, forming a Nafion layer on the Teflon layer. This layer is referred to as "StratIon."

[0097] The StratIon layer is transferred by decal onto a dry proton exchange membrane (called "Membr") with a thickness of 15 microns and a proton exchange capacity equal to 2.94 milliequivalents per gram. The transfer is carried out by a hot pressing procedure, in which the system is held at 130°C for 5 minutes and a pressure of 5.52 MPa is employed. The resulting product is called "Membr+StratIon".

[0098] The Membr+StratIon is subjected to the following activation procedure: (i) wash with bidistilled water at 80° C. for 1 hour, (ii) wash with 3% H2O2 at 80° C. for 1 hour, (iii) wash twice with 1 M H2SO4 at 80° C. for 1 hour, (iv) wash once with bidistilled water at 80° C. for 1 hour. The Membr+StratIon is then dried with a dry air stream for 24 hours before use in MEA fabrication.

[0099] 20 mg of PtNi2 and 10 mg of Vulcan XC-72R carbon black were combined and vigorously ground. The resulting mixture was placed in a vial, and 200 microliters of double-distilled water was added, followed by 1 milliliter of isopropyl alcohol. 22.95 mg of ZnO in the form of nanoparticles with an average diameter of 50 nm was further added to the suspension. The resulting suspension was vigorously sonicated using a tip sonicator, and 366 microliters of a 5 wt% Nafion alcohol dispersion was added to the suspension. The resulting suspension was vigorously sonicated using a tip sonicator, and the resulting product was a suspension designated "SospCat."

[0100] 20 mg of standard EC (containing 20 wt. % platinum, designated "Pt / C Standard 2") is placed in a vial, and 200 microliters of double-distilled water is added, followed by 1 milliliter of isopropyl alcohol. The resulting suspension is vigorously sonicated using a tip sonicator. Next, 206 microliters of a 5 wt. % Nafion alcohol dispersion is added to the suspension. The suspension is vigorously sonicated using a tip sonicator, and the resulting product is a suspension designated "SospAn."

[0101] 10.09 mg of SospCat was applied to a 2 x 2 cm Teflon sheet. The solvent was then removed by drying at 90°C to form a layer deposited on the Teflon layer. This layer was called "EletCat."

[0102] The EletCat layer is transferred onto the Membr+StratIon layer on the side facing the StratIon layer using a decal. Specifically, the EletCat is positioned completely inside the StratIon layer. This transfer is carried out by a hot pressing procedure, in which the system is kept at 130°C for 5 minutes and a pressure of 5.52 MPa is applied. The resulting product is called "Membr+StratIon+EletCat."

[0103] The Membrane + StratIon + EletCat is treated with 0.5 M HNO3 solution at room temperature for 1 hour. This treatment is repeated three times. The Membrane + StratIon + EletCat is then washed with bidistilled water at room temperature for 20 minutes. This treatment is repeated twice. The Membrane + StratIon + EletCat is then dried with a dry air stream for 24 hours.

[0104] An aliquot of SospAn was applied to the microporous layer of a 2 x 2 cm Teflon-coated carbon paper electrode so that the total platinum loading on the electrode was equal to 0.4 milligrams of platinum per square centimeter of electrode. To achieve this, the weight of the solids deposited on the electrode (obtained by drying the SospAn suspension) should be equal to 11.84 mg. The resulting electrode is referred to as the "Pt / C Reference 2 Anode."

[0105] A Pt / C reference 2 anode electrode was placed in direct contact with the Membr+StratIon+EletCat layer on the side where the StratIon and EletCat layers had not been transferred. Alternatively, a 2 x 2 cm square of Teflon-coated carbon paper with a microporous layer was attached to the other side of the Membr+StratIon+EletCat layer, the side on which the StratIon and EletCat layers had been transferred. Specifically, this microporous layer was placed in contact with the EletCat layer. The resulting system consisting of the Pt / C reference 2 anode electrode, the Membr+StratIon+EletCat layer, and the 2 x 2 cm square of Teflon-coated carbon paper with a microporous layer was subjected to a hot pressing process at a temperature of 146 °C and a pressure of 2.76 MPa (maintaining these parameters for 5 minutes). At the end of this process, an MEA designated MEA3 was obtained.

[0106] A second MEA, designated MEA 4, is prepared, which is identical to MEA 3 with the only difference being that MEA 4 does not contain 50 nm diameter ZnO nanoparticles in the EletCat layer.

[0107] MEAs 3 and 4 are tested in single cells, and the corresponding polarization curves are shown in Figure 1.

[0108] It was observed that the introduction of ZnO particles into EletCat and their subsequent removal by acid treatment significantly improved the maximum current density delivered by MEA3. The flooding phenomenon is suppressed due to the improved accessibility of the active site present in EletCat (reactants can reach the active site more easily and products can be better expelled from the active site).

[0109] Example 3 This Example 3 relates to an EC designated "PtNi1." EC PtNi1 was prepared as described in WO 2017 / 055981 and WO 2018 / 122368. PtNi1 contained 9.0 wt.% Pt and 3.1 wt.% Ni. 50 mg of PtNi1 was mixed with 50 mg of Vulcan XC-72R carbon black. The resulting mixture was thoroughly ground in a mortar to obtain a mixture designated "initial PtNi1." The preparation of this mixture is described in V. Di Noto et al., Adv. Funct. Mater. 17 (2007) 3626-3638. A small amount (approximately 5 mg) of PtNi1 was added to 76.5 mg of ZnO nanoparticles with an average diameter of 50 nm. The resulting mixture was vigorously ground in a mortar. Subsequently, a small amount of additional PtNi1 is added to the resulting mixture, and this process (PtNi1 addition + mixture grinding) is repeated until the mixture contains a total of 50 mg of PtNi1. Subsequently, a total of 50 mg of Vulcan XC-72R carbon black is added to the resulting mixture. Again, the addition is carried out in small increments by vigorously grinding the intermediate mixture in a mortar. The final mixture, containing a total of 50 mg of PtNi1, 50 mg of Vulcan XC-72R carbon black, and 76.5 mg of ZnO nanoparticles with an average diameter of 50 nm, is referred to as "treated PtNi1." Each mixture is then used to prepare inks using the formulation method described in V. Di Noto et al., Adv. Funct. Mater. 17 (2007) 3626-3638.

[0110] Next, appropriate amounts of these inks are deposited onto the RRDE chip to achieve a platinum loading of 12 micrograms per square centimeter on the RRDE chip disk. The solvent is removed by the procedure described in Y. Garsany et al., J. Electroanal. Chem. 662 (2011) 396-406 and P.J. Yunker et al., Nature 476 (2011) 308-311. At the end of this drying step, the RRDE chip has the appearance shown in Figure 3.

[0111] It is noteworthy that the deposited layer containing the "treated PtNi1" mixture is much denser and more homogeneous than the deposited layer containing the "pristine PtNi1" mixture. Each RRDE chip was used to perform "ex situ" measurements of EC performance using the CV-TF-RRDE technique, as described in V. Di Noto et al., Adv. Funct. Mater. 17 (2007) 3626-3638 and V. Di Noto et al., Electrochim. Acta 280 (2018) 149-162. Similarly, CV-TF-RRDE measurements were performed using a reference EC containing 10 wt.% platinum, designated the "Pt / C reference." This EC was introduced into the ink without further addition of either Vulcan XC-72R carbon black or any additional solid components. A layer containing the EC Pt / C reference was deposited on the RRDE chip disc and dried as previously described. The platinum loading in this layer is equal to 12 micrograms per square centimeter. All RRDE measurements are collected at T = 25 °C by rotating the RRDE tip at 1,600 rpm. The results are shown in Figure 4.

[0112] The current density in the ORR (J ORR (expressed as) is approximately -1.5mAcm (absolute value) -2 It is interesting to note how the two profiles match when the maximum J obtained for the "treated PtNi1" is lower than ORR (approx. -5.7 mAcm -2 (equal to the maximum J obtained for the "initial PtNi1" mixture)ORR (about -4mAcm -2 This result is significantly higher (in absolute value) than the maximum J ORR This is due to the fact that the value is directly proportional to the area of ​​the RRDE chip disk that is actually covered with EC. This area is larger in the case of the deposited and dried layer containing the "treated PtNi1" mixture (see Figure 3(b)) than in the case of the deposited and dried layer containing the "pristine PtNi1" mixture (see Figure 3(a)). In fact, in the latter case, most of the area of ​​the RRDE chip disk is not covered by the mixture containing EC.

[0113] The results presented in this Example 3 demonstrate that the present invention provides a mixture containing EC PtNi1 characterized by high homogeneity. Furthermore, the preparation procedure described herein does not adversely affect the performance of EC PtNi1 in ORR, nor does it adversely affect the number and chemical nature of the active sites present in the EC.

[0114] Example 4 This Example 4 relates to EC designated "PtCu1." EC PtCu1 was prepared as described in WO 2017 / 055981 and WO 2018 / 122368. PtCu1 contained 29.5 wt% Pt, 4.75 wt% Cu, and 0.055 wt% Ni. 50 mg of PtCu1 was mixed with 50 mg of Vulcan XC-72R carbon black. The resulting mixture was thoroughly ground in a mortar to obtain a mixture designated "initial PtCu1." The preparation of this mixture is described in V. Di Noto et al., Adv. Funct. Mater. 17 (2007) 3626-3638. A small amount (approximately 5 mg) of PtCu1 was added to 58 mg of ZnO nanoparticles with an average diameter of 50 nm. The resulting mixture was vigorously ground in a mortar. Subsequently, a small amount of PtCu1 is added to the resulting mixture, and this process (PtCu1 addition + mixture grinding) is repeated until the mixture contains a total of 50 mg of PtCu1. Subsequently, a total of 50 mg of Vulcan XC-72R carbon black is added to the resulting mixture. Again, the addition is carried out in small increments by vigorously grinding the intermediate mixture in a mortar. The final mixture, containing a total of PtNi1, 50 mg of Vulcan XC-72R carbon black, and 58 mg of ZnO nanoparticles with an average diameter of 50 nm, is referred to as "treated PtCu1." Each mixture is then used to prepare inks using the formulation method described in V. Di Noto et al., Adv. Funct. Mater. 17 (2007) 3626-3638. An appropriate amount of these inks is then deposited on an RRDE chip to achieve a platinum loading of 12 micrograms per square centimeter on the RRDE chip disk. The solvent is removed by the procedure described in Y. Garsany et al., J. Electroanal. Chem. 662 (2011) 396-406 and PJ Yunker et al., Nature 476 (2011) 308-311. At the end of this drying step, the RRDE chip has the appearance shown in Figure 5.

[0115] It is noteworthy that the deposited layer containing the "treated PtCu1" mixture is much denser and more homogeneous than the deposited layer containing the "initial PtCu1" mixture (which has a ring-shaped morphology, indicating a very low amount of mixture in the central region). Each RRDE chip was used to perform "ex situ" measurements of EC performance using the CV-TF-RRDE technique, as described in V. Di Noto et al., Adv. Funct. Mater. 17 (2007) 3626-3638 and V. Di Noto et al., Electrochim. Acta 280 (2018) 149-162. Similarly, CV-TF-RRDE measurements using a reference EC were performed as described in Example 3. All RRDE measurements were collected by rotating the RRDE chip at 1,600 rpm at T = 25 °C. The results are shown in Figure 6.

[0116] The current density in the ORR (J ORR (expressed as) is approximately -1.5mAcm (absolute value) -2 It is interesting to note how the two profiles match when the maximum J obtained for "treated PtCu1" is lower than ORR (about -4.5mAcm -2 (equal to the maximum J obtained for the "initial PtCu1" mixture) ORR (approx. -3.9mAcm -2 This result is significantly higher (in absolute value) than the maximum J ORR This is due to the fact that the value is directly proportional to the area of ​​the RRDE chip disk that is actually covered with EC. This area is larger in the case of the deposited and dried layer containing the "treated PtCu1" mixture (see Fig. 5(b)) than in the case of the deposited and dried layer containing the "pristine PtCu1" mixture (see Fig. 5(a)). In fact, in the latter case, most of the area of ​​the RRDE chip disk is not covered by the mixture containing EC.

[0117] The results presented in this Example 4 are similar to those presented in Example 3 and demonstrate that the present invention allows for the production of mixtures containing EC PtCu1 characterized by high homogeneity. Furthermore, the preparation procedures described herein do not adversely affect the performance of EC PtCu1 in ORR, nor the number and chemical nature of the active sites present in the EC.

[0118] Example 5 This Example 5 relates to an EC designated "PtNi3." EC PtNi3 was prepared as described in WO 2017 / 055981 and WO 2018 / 122368. PtNi3 contains 5.71 wt. % Pt and 3.32 wt. % Ni. Fabrication of an MEA containing EC PtNi3 is carried out as follows.

[0119] A total of 250 microliters of a 5 wt% Nafion alcohol dispersion is spread onto a Teflon™ sheet to form a square with an area equal to 5 square centimeters. This is followed by drying at 90°C to remove the solvent, resulting in a Nafion layer on the Teflon layer. This layer is referred to as "StratIon." Two separate "StratIon" layers are fabricated on two separate Teflon sheets.

[0120] The StratIon layer is transferred by decal onto both sides of a dry proton exchange membrane (called "Membr") with a thickness of 15 microns and a proton exchange capacity equal to 2.94 milliequivalents per gram. The transfer is carried out by a hot pressing procedure, in which the system is held at 130°C for 5 minutes and a pressure of 5.52 MPa is employed. The resulting product is called "Membr+StratIon".

[0121] The Membr+StratIon is subjected to the following activation procedure: (i) wash with bidistilled water at 80° C. for 1 hour, (ii) wash with 3% H2O2 at 80° C. for 1 hour, (iii) wash twice with 1 M H2SO4 at 80° C. for 1 hour, (iv) wash once with bidistilled water at 80° C. for 1 hour. The Membr+StratIon is then dried with a dry air stream for 24 hours before use in MEA fabrication.

[0122] 20 mg of PtNi3, 10 mg of Vulcan XC-72R carbon black, and 22.95 mg of ZnO nanoparticles (with an average diameter of 50 nm) were used to obtain a mixture designated "treated PtNi3." This mixture was prepared according to the procedure described in Example 3 to obtain a mixture designated "treated PtNi1." The resulting mixture was placed in a vial, and 200 microliters of double-distilled water was added, followed by 1 milliliter of isopropyl alcohol. The resulting suspension was vigorously sonicated using a tip sonicator, and 364 microliters of a 5 wt% Nafion alcohol dispersion was added to the suspension. The suspension was vigorously sonicated using a tip sonicator, and the resulting product was a suspension designated "SospCat."

[0123] To 20 mg of standard EC (containing 20 wt. % platinum, designated "Pt / C Standard 2") in a vial, 200 microliters of double-distilled water is added, followed by 1 milliliter of isopropyl alcohol. The resulting suspension is vigorously sonicated using a tip sonicator. Next, 206 microliters of a 5 wt. % Nafion alcohol dispersion is added to the suspension. The suspension is subjected to thorough sonication using a tip sonicator, and the resulting product is a suspension designated "SospAn."

[0124] 10.08 mg of SospCat was applied to a 2 x 2 cm Teflon sheet. The solvent was then removed by drying at 90°C to form a layer deposited on the Teflon layer. This layer was called "EletCat."

[0125] The EletCat layer is transferred to one of the two surfaces of the Membr+StratIon (the surface covered with the StratIon layer). Specifically, the EletCat is positioned completely inside the StratIon layer. This transfer is carried out by a hot pressing procedure, in which the system is kept at 130°C for 5 minutes and a pressure of 5.52 MPa is applied. The resulting product is called "Membr+StratIon+EletCat."

[0126] The Membrane + StratIon + EletCat is treated with 0.5 M HNO3 solution at room temperature for 1 hour. This treatment is repeated three times. The Membrane + StratIon + EletCat is then washed with bidistilled water at room temperature for 20 minutes. This treatment is repeated twice. The Membrane + StratIon + EletCat is then dried with a dry air stream for 24 hours.

[0127] An aliquot of SospAn was applied to the microporous layer of a 2 x 2 cm Teflon-coated carbon paper electrode so that the total platinum loading on the electrode was 0.4 milligrams of platinum per square centimeter of electrode. To achieve this, the weight of the solids deposited on the electrode (obtained by drying the SospAn suspension) should be equal to 11.84 mg. The resulting electrode is referred to as the "Pt / C Reference 2 Anode."

[0128] A Pt / C reference 2 anode electrode was placed in direct contact with the Membr+StratIon+EletCat layer on the side where the EletCat layer had not been transferred. Alternatively, a 2 × 2 cm square of Teflon-coated carbon paper with a microporous layer was attached to the other side of the Membr+StratIon+EletCat, the side on which both the StratIon and EletCat layers had been transferred. Specifically, this microporous layer was placed in contact with the EletCat layer. The resulting system consisting of the Pt / C reference 2 anode electrode, the Membr+StratIon+EletCat layer, and the 2 × 2 cm square of Teflon-coated carbon paper with a microporous layer was subjected to a hot-press process at 146 °C and 2.76 MPa (maintaining these parameters for 5 minutes). At the end of this process, an MEA designated MEA5 was obtained.

[0129] A second MEA, designated MEA 6, is prepared. MEA 6 is identical to MEA 5 with the only difference being that ZnO nanoparticles with a diameter equal to 50 nm are not milled together with PtNi3, but are simply added to SospCat together with a mixture obtained by vigorously milling 20 mg of PtNi3 with 10 mg of Vulcan XC-72R carbon black.

[0130] MEAs 5 and 6 are tested in single cells, and the corresponding polarization curves are shown in Figure 7.

[0131] Figure 7 shows how much greater the current density generated by MEA5 is than that generated by MEA6, especially at low cell potentials. This result can be interpreted as follows: Both MEA5 and MEA6 contain EletCat layers obtained starting from the same amounts of PtNi3, Vulcan XC-72R carbon black, ZnO nanoparticles with a diameter equal to 50 nm, and SospCat characterized by Nafion. However, in MEA5, the ZnO nanoparticles were vigorously milled with EC PtNi3, whereas in MEA6, the same nanoparticles were added to SospCat without being milled. As a result, MEA5 contains much denser and more homogeneous EletCat than MEA6, likely due to the reduced size of the PtNi3 particles caused by the milling process. Thus, the acid treatment and subsequent removal of the 50-nm-diameter ZnO nanoparticles improves the accessibility of the active sites present in the EletCat of MEA5 compared to the active sites present in the EletCat of MEA6. In conclusion, compared with MEA6, the active sites of MEA5 are more accessible to reactants and can better expel products, thus suppressing the flooding phenomenon.

[0132] The performance of MEA5, in which ZnO acts as both a grinding agent and a pore former, is much better than that of MEA6, in which ZnO was simply added to the ink after grinding the electrocatalyst and therefore only served as a pore former. These results suggest that the introduction of ZnO as both a grinding agent and a pore former has a significant effect in improving the performance of the MEA because (i) the formed cavities significantly improve the distribution of reactants within the electrocatalyst layer and (ii) the particle size of the electrocatalyst is reduced, increasing its surface area and the accessibility of the active sites.

Claims

1. A method for producing a membrane-electrode assembly, the membrane-electrode assembly comprising: an anode and a cathode facing each other; an ion exchange membrane placed between the anode and the cathode; - electrocatalytic layers applied to both sides of the ion exchange membrane; an ion exchange polymer layer disposed between said membrane and at least one of the electrocatalytic layers; Including, the electrocatalytic layer comprises micropores having an average diameter between 0.001 micrometers and 50 micrometers; the electrocatalyst layer comprises electrocatalyst particles having an average diameter between 0.01 micrometers and 10 micrometers; the electrocatalyst layer comprises a carbonitride-based electrocatalyst having a "core-shell" morphology; The method comprises: (a) providing a dispersion of an ion exchange polymer in a protic polar solvent or in a solution comprising two or more protic polar solvents; (b) applying the dispersion onto an ion exchange membrane or onto at least one electrocatalytic layer applied onto said membrane by (i) direct application onto said membrane or onto said at least one electrocatalytic layer, or (ii) application onto an inert substrate followed by transfer onto said membrane or onto said at least one electrocatalytic layer to form a membrane-polymer layer system or an electrocatalytic layer-polymer layer system; (c) removing the solvent; Including, further comprising the steps of introducing at least one pore-forming agent into the electrocatalyst layer and subsequently removing said at least one pore-forming agent from the electrocatalyst layer; the electrocatalyst particles have an average diameter between 0.01 micrometers and 10 micrometers, the particles being obtained using the steps of grinding an initial electrocatalyst in the presence of at least one grinding agent and subsequently removing the at least one grinding agent from the particles; The pore-forming agent and the grinding agent are ZnO, TiO 2 , or SiO 2 are the same metal oxides selected from A method characterized by:

2. The method of claim 1, further comprising the step of (d) applying pressure to the membrane-polymer layer system or the electrode catalyst layer-polymer layer system and / or treating the system with at least one acidic or basic aqueous solution.

3. 3. The method of claim 1, wherein the pore-forming agent consists of particles having an average diameter between 200 nm and 20 nm.

4. 4. The method according to claim 1, wherein the grinding agent consists of particles having an average diameter between 1 mm and 2 nm.

5. 5. The method of claim 4, wherein the grinding agent comprises particles having an average diameter between 100 nm and 10 nm.

6. 6. The method according to any one of claims 1 to 5, wherein the milling step is carried out for a time ranging from 20 minutes to 400 hours, and the milling step is carried out at a temperature between -270°C and 1700°C.

7. 7. The method according to claim 1, wherein the grinding step is carried out in the presence of a liquid, the liquid being selected from water, alcohols, aldehydes, ketones, ethers, esters, hydrocarbons, amines, amides, or mixtures thereof.

8. 8. The method according to claim 1, wherein the electrode catalyst layer comprises an electrode catalyst material, and the ratio of a volume of a pore-forming agent or a grinding agent introduced into the electrode catalyst layer to a volume of the electrode catalyst material contained in the electrode catalyst layer is in the range of 10 to 0.

01.

9. 9. The method of claim 8, wherein the ratio of the volume of the pore-forming agent or grinding agent introduced into the electrode catalyst layer to the volume of the electrode catalyst material contained in the electrode catalyst layer is in the range of 1 to 0.

1.

10. 10. The method according to any one of claims 1 to 9, wherein the removal step of the pore-forming agent and the grinding agent is achieved by: (i) washing with an acidic or basic aqueous solution; (ii) vacuum sublimation; (iii) ultrasonic treatment; (iv) decantation; (v) filtration; (vi) addition of a suitable additive followed by flotation; (vii) treatment with a non-polar organic solvent such as toluene, hexane, heptane, benzene, or a mixture thereof; (viii) treatment with an aprotic polar solvent such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, or a mixture thereof; or (ix) treatment with aldehydes, ketones, carboxylic acids, amines, or a mixture thereof.

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