Method for preparing an electrochemically activated electrode based on supported mos2 for electrochemical reduction reactions

Abstract

Disclosed is a method for preparing an electrochemically activated electrode for electrochemical reduction reactions, the electrode comprising at least one catalytic material based on at least one group VIB metal supported on an electrically conductive support, the method consisting in carrying out an electrochemical treatment on an electrode comprising at least one catalytic material based on at least one group VIB metal supported on an electrically conductive support. The electrochemical treatment, which is carried out by cyclic voltammetry (CV) or chronoamperometry (CA), consists of a step of oxidation under specific conditions.

Description

[0001] METHOD FOR PREPARING AN ELECTROCHEMICALLY ACTIVATED MOS2-BASED ELECTRODE SUPPORTED FOR ELECTROCHEMICAL REDUCTION REACTIONS

[0002] technical field

[0003] The present invention relates to the field of electrodes suitable for use in electrochemical reduction reactions, in particular for the electrolysis of water to produce hydrogen.

[0004] State of the art

[0005] To achieve the goals of the energy transition, manufacturers are now focusing on the production and use of low-carbon, renewable hydrogen (or dihydrogen H2). Currently used primarily in the chemical and refining industries, this energy carrier could contribute to decarbonizing certain industrial sectors, ensuring electricity storage, or powering the transportation sector.

[0006] Various production techniques exist:

[0007] • Steam reforming of natural gas is the most widespread technique. It involves reacting methane with water to obtain a mixture containing hydrogen and CO2.

[0008] • Gasification allows the production, through combustion, of a mixture of CO and H2 from coal or biomass. The CO2 emitted in the two previous cases could potentially be captured and stored or utilized.

[0009] • Hydrogen can also be produced from water and electricity; this is water electrolysis. This is the most promising method because it is a clean production method (no carbon emissions when coupled with a renewable energy source) and provides high-purity hydrogen, but it remains expensive (2 to 3 times more expensive than natural gas reforming).

[0010] In a water electrolysis cell, the hydrogen evolution reaction (HER) occurs at the cathode and the oxygen evolution reaction (OER) at the anode. The overall reaction is:

[0011] H2O H2+1 / 2 O2

[0012] Catalysts are required for both reactions. Various metals have been studied as catalysts for the dihydrogen production reaction at the cathode, and these differ depending on the technology and therefore the physicochemical conditions under which the catalysts operate. Today, platinum is the most widely used metal in membrane electrolyzers, particularly in acidic environments, in proton exchange membrane (PEM) electrolyzers. It exhibits an overpotential (the voltage required to produce one H2 molecule from two H2 molecules). +negligible compared to other metals. However, the scarcity, cost (> €25k / kg), and competing uses (fuel cells, catalysis, etc.) of this noble metal are hindering the long-term economic development of the hydrogen sector. This is why, for several years now, researchers have been focusing on new catalysts, without platinum, but based on inexpensive and abundant metals found in nature.

[0013] The production of hydrogen by water electrolysis is well described in the book "Hydrogen Production: Electrolysis," 2015, published by Agata Godula Jopek. Water electrolysis is an electrolytic process that decomposes water into gaseous O2 and H2 using an electric current. The electrolytic cell consists of two electrodes—usually made of an inert metal (within the relevant potential and pH range), such as platinum—immersed in an electrolyte and connected to opposite poles of the direct current source.

[0014] The electric current dissociates the water molecule at the anode by following the oxidation reaction:

[0015] H2O(I) 1 / 2 O2(g) + 2 H+ (aq)+ 2e~

[0016] This is also referred to as the OER (Oxygen Evolution Reaction).

[0017] Next, the protons H +migrate towards the cathode through the membrane under the effect of the electric field and the concentration gradient where they are reduced to molecular hydrogen (with electrons coming from the negative pole of the generator), hence the name of this electrolyzer technology "proton exchange membrane".

[0018] Therefore, at the cathode, the protons H + accept electrons by forming hydrogen gas (H2), according to the reduction reaction:

[0019] 2 hours + + 2 e- ^ H2

[0020] This is also referred to as the HER (Hydrogen Evolution Reaction).

[0021] The composition and use of catalysts for hydrogen production by water electrolysis are extensively covered in the literature. A review article summarizing the families of interesting materials under development over the past decade is: PCK Vesborg et al., "Recent Development in Hydrogen Evolution Reaction Catalysts and Their Practical Implementation," 2015, in which the authors describe sulfides, carbides, and phosphides as potential new electrocatalysts. Among the sulfide phases, dichalcogenides such as molybdenum sulfide (MOS2) are very promising materials for the hydrogen evolution reaction (HER) due to their high activity, excellent stability, and availability, as molybdenum and sulfur are abundant and inexpensive elements on Earth.They are particularly well described in the review article on M0S2 for an application in HER: “Improving intrinsic electrocatalytic activity of layered transition metal chalcogenides as electrocatalysts for water splitting” AP Tiwari, K. Kim and S. Jeon, in Current Opinion in Electrochemistry, 2022, 34,100982.

[0022] M0S2-based materials have a lamellar structure. The active phases can be used in bulk form when electron conduction from the cathode is sufficient, or in a supported state, which then involves a support of a different nature. In the latter case, the support must have specific properties:

[0023] - large specific surface area to promote the dispersion of the active phase;

[0024] - very good electronic conductivity;

[0025] - chemical and electrochemical stability under water electrolysis conditions (acidic medium and high potential).

[0026] Carbon is the most commonly used substrate in this application. The key challenge lies in preparing this sulfide phase on the conductive material.

[0027] It is generally accepted that a catalyst with high catalytic potential is characterized by an associated active phase that is perfectly dispersed across the surface of the support and has a high active phase content. Ideally, the catalyst should also offer accessibility of its active sites to the reactants, in this case protons, while simultaneously developing a large active surface area. This can lead to specific constraints in terms of structure and texture, inherent to the support constituting these catalysts.

[0028] The usual methods leading to the formation of the active phase of catalytic materials for the electrolysis of water consist of a deposition of precursor(s) comprising at least one metal from group VIB, and possibly at least one metal from group VIII, on a support by the so-called "dry impregnation" technique or by the so-called "excess impregnation" technique, followed by at least one possible heat treatment to remove the water and a final sulfidation step generating the active phase, as mentioned above.

[0029] It appears promising to find methods for preparing catalysts for hydrogen production by water electrolysis, enabling the development of new catalysts with improved performance. The improved electrocatalytic performance of electrocatalysts composed of MoS2 can be described by the two principles proposed by Li Xin Chen et al., "Design of Dual-Modified MoS2 with Nanoporous Ni and Graphene as Efficient Catalysts for the Hydrogen Evolution Reaction," 2018: increasing the number of active sites or their intrinsic activity.

[0030] Regarding the increase in the number of active sites, we can cite nanoporous structures, heterostructures, and 3D, 2D, or 1D morphologies such as nanoflowers, nanosheets, or nanotubes (see article by D. Vory et al., "Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution," 2013). The creation of new active sites through doping and / or the creation of sulfur vacancies, potentially filled by Mo atoms, particularly on the basal plane, as described in the articles by N. Abidi et al., "Revisiting the Active Sites at the MOS2 / H2O Interface via Grand-Canonical DFT: The Role of Water Dissociation," 2020, and "How to dope the basal plane of 2H-M0S2 to boost the hydrogen evolution reaction?", 2023.

[0031] Regarding increasing the intrinsic activity of active sites, numerous strategies are also conceivable, including:

[0032] - The integration of conductive nanomaterials such as graphene or nanoporous metals, described in the article by J Joyner "Graphene Supported M0S2 Structures with High Defect Density for an Efficient HER Electrocatalysts", 2020.

[0033] - Reinforcement of the intrinsic activity of the edges via doping with nanoporous nickel for example as described in the article by LX Chenet al., "Design of Dual-Modified M0S2 with Nanoporous Ni and Graphene as Efficient Catalysts for the Hydrogen Evolution Reaction", 2018.

[0034] Another method described in the literature for improving the performance of an electrocatalyst is electrochemical treatment (or pretreatment) of the electrode before use. This pretreatment involves polarizing the catalyst under specific operating conditions and at targeted potentials to enhance its performance. Depending on the conditions applied, this pretreatment can clean the catalyst surface by desorbing impurities and modify it by, for example, promoting oxidation, reduction, or the creation of defects.

[0035] An example of pretreatment of a thin platinum film prior to cyclic voltammetry measurements is described in M. Josowicz's article "Electrochemical Pretreatment of Thin Film Platinum Electrodes," 1988. The pretreatment removes traces of transition metal oxides used during platinum layer deposition. It consists of applying potential peaks between 0 and 2 V in a solution of EDTA, NH4OH, and µCh followed by potential cycles in a KNO3 solution.

[0036] The effects of various electrochemical treatments on M0S2 have been described in the literature. C. Tsai, in "Electrochemical generation of sulfur vacancies in the basal plane of M0S2 for hydrogen evolution" (2017), describes the effect of a cathodic (reducing) treatment on M0S2 2H nanosheets, deposited or not on a carbon foam. This treatment creates sulfur vacancies in the basal plane. These vacancies appear to improve the HER catalytic properties of the catalyst. The current can be increased up to 5 times at -320 mV vs. EN H with and without pretreatment. Conversely, an anodic (oxidizing) treatment also promotes vacancies and oxygen insertion. This was demonstrated by X. Gan in "2H / 1T Phase Transition of Multilayer M0S2 by Electrochemical Incorporation of S Vacancies", 2018. He also observed a transition from a 2H to a 2T phase thanks to these oxidative treatments. P.Gaigalas, in his 2024 study "The enhancement of hydrogen evolution reaction on nanoplatelet-shaped MoS2 via anodic pretreatment," also investigated the effect of oxidative treatment using cyclic voltammetry at different potentials on the HER performance of an M0S2 film deposited on a titanium substrate. According to this study, excursions up to +0.75 V vs EN H were the most effective, increasing the current from 95 to 140 mA·cm'. 2at 0.350 V vs ENH. Treatments at higher potentials tend to reduce performance. J. Bonde, in "Hydrogen evolution on nano-particulate transition metal sulfides" (2008), explained the mechanisms involved at high potentials. He demonstrated, using M0S2 deposited on carbon paper, that above 0.7 V vs ENH, M0S2 oxidized, which deactivated it in the long term. Therefore, he did not explore this approach for pretreating the catalyst. Ultimately, none of these studies proposes an oxidation activation protocol for M0S2 supported and dispersed on an electrically conductive support such as carbon, allowing for a tangible performance gain.

[0037] Object of the invention

[0038] The Applicant has developed a new process for preparing an electrode usable in an electrolytic cell for carrying out electrochemical reduction reactions, and more particularly enabling the production of a cathode usable in an electrolytic cell for the production of hydrogen by electrolysis of water in an acidic medium.Indeed, the Applicant has discovered that an oxidative electrochemical treatment, preceded or not by a reductive electrochemical treatment, of a nanostructured material based on at least one group VI B sulfide metal supported on an electroconductive support allows for catalytic performance that is at least as good, or even better, particularly when the latter is used as a catalytic phase of an electrode for electrochemical reduction reactions, and even more particularly when the said electrode is used as a cathode for the production of hydrogen by electrolysis of water in an acidic medium.

[0039] A first object of the invention relates to a method for preparing an electrochemically activated electrode for electrochemical reduction reactions, said electrode comprising at least one catalytic material based on at least one metal of group VI B supported on an electroconductive support, said method comprising at least the following steps: a) supplying an electrode comprising at least one catalytic material based on at least one metal of group VIB supported on an electroconductive support; b) carrying out an electrochemical oxidative treatment of the electrode supplied in step a) by cyclic voltammetry (CV) or chronoamperometry (CA) to obtain an electrochemically activated electrode, said treatment being characterized by the use of an oxidation potential applied to the electrode of between 0 V vs ENH and 2.5 V vs ENH.

[0040] Advantageously, between step a) and step b) a reductive electrochemical treatment step is carried out, characterized by the use of a reduction potential applied to the electrode between -0.25 V vs ENH and -2 V vs ENH.

[0041] Preferably, the oxidative electrochemical treatment of step b) is characterized by the use of an oxidation potential applied to the electrode between 0.5 V vs ENH and 1.3 V vs ENH.

[0042] Advantageously, the oxidative electrochemical treatment of step b) is carried out between 1 and 5 times successively with increasing oxidizing potentials.

[0043] Advantageously, the scan rate used in the cyclic voltammetry oxidative electrochemical treatment of step b) is between 1 mV.s -1 and 100 mV.s' 1 .

[0044] Advantageously, the number of cycles used in the cyclic voltammetry oxidative electrochemical treatment of step b) is between 1 and 100.

[0045] Advantageously, the duration of the electrochemical oxidative treatment by chronoamperometry in step b) is between 1 minute and 600 minutes. Preferably, the duration of the electrochemical oxidative treatment by chronoamperometry in step b) is between 30 minutes and 300 minutes.

[0046] Advantageously, in step a) said metal of group VI B is molybdenum.

[0047] Advantageously, in step a) the electro-conductive support is carbon.

[0048] Advantageously, in step a) the content of group VI B metal in the catalytic material is between 4 and 60% by weight relative to the total weight of the catalytic material.

[0049] Advantageously, at step a) the surface density which corresponds to the quantity of group VI B metal atoms deposited per unit surface area of ​​support is between 0.5 and 20 atoms of metallic element per square nanometer of support.

[0050] Another object of the invention relates to an electrolysis device comprising an anode, a cathode, an electrolyte, said device being characterized in that at least one of the anode or cathode is an electrode prepared according to the invention.

[0051] Another object of the invention relates to the use of the electrolysis device according to the invention in electrochemical reactions.

[0052] Preferably, said device is used as:

[0053] - water electrolysis device for the production of a gaseous mixture of hydrogen and oxygen and / or the production of hydrogen alone;

[0054] - nitrogen electrolysis device for the production of ammonia;

[0055] - carbon dioxide electrolysis device for the production of formic acid, CO and ethylene;

[0056] - fuel cell device for the production of electricity from hydrogen and oxygen.

[0057] Detailed description of the invention

[0058] Definitions

[0059] In what follows, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81 ème edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IIIPAC classification.

[0060] BET surface refers to the specific surface area determined by nitrogen adsorption in accordance with ASTM D 3663-78, established from the BRUNAU ER - EMMET - TELLER method described in the periodical "The Journal of the American Chemical Society", 60, 309 (1938).

[0061] Electrode

[0062] An electrode is the layer containing the catalytic material that is the site of electrochemical reactions.

[0063] Current collector

[0064] A current collector is a layer that allows the transport of electrons to or from the electrodes. It can be dense, like glassy carbon in a three-electrode setup, or porous, like the PTL (Porous Transport Layer) or the bipolar plate used for fluid transport in an electrolyzer.

[0065] Ink

[0066] An ink is a mixture of powdered active material (here based on at least one metal from group VIB sulfide), a conductive agent, a binding agent, and a solvent that forms part of the electrode formulation. This "ink" is then deposited on the current collector or on the cathode side of the membrane and dried, which, after assembly, yields the electrode that is positioned between the current collector and the membrane.

[0067] Cyclic Voltammetry

[0068] Cyclic voltammetry (CV) is an electrochemical technique that involves sweeping a working electrode relative to a reference electrode through a potential range between an initial potential and maximum and minimum potentials, and measuring the current. A positive current is conventionally considered an oxidation current, and a negative current, a reduction current. The sweep cycle can be repeated multiple times.

[0069] Chronoamperometry

[0070] Chronoamperometry (CA) is an electrochemical technique that involves applying a potential to a working electrode relative to a reference electrode and measuring the change in current over time.

[0071] Normal hydrogen electrode All potentials are expressed with respect to a reference electrode whose potential is known and fixed: the normal hydrogen electrode (NHE).

[0072] The metal content of group VI B is measured by X-ray fluorescence and is given as a percentage by weight relative to the total mass of the catalytic material.

[0073] Method for preparing the electrochemically activated electrode

[0074] The present invention relates to a method for preparing an electrochemically activated electrode for electrochemical reduction reactions, said electrode comprising at least one catalytic material based on at least one metal of group VI B supported on an electroconductive support, said method comprising at least the following steps: a) supplying an electrode comprising at least one catalytic material based on at least one metal of group VIB supported on an electroconductive support; b) carrying out an oxidative electrochemical treatment of the electrode supplied in step a) by cyclic voltammetry (CV) or chronoamperometry (CA) to obtain an electrochemically activated electrode, said treatment being characterized by the use of an oxidation potential applied to the electrode of between 0 V vs ENH and 2.5 V vs ENH.

[0075] Steps a) and b) are described in detail below.

[0076] Step a) Electrode supply

[0077] According to step a) of the process according to the invention, an electrode comprising at least one catalytic material based on at least one metal from group VIB supported on an electroconductive support is supplied.

[0078] The electrode can be prepared according to techniques well known to those skilled in the art. According to one or more embodiments, the electrode is formulated by a preparation process comprising the following substeps: a1) an ink is prepared by carrying out the following substeps: a1.1) at least one ionically conductive polymer binder is dissolved in a solvent or a mixture of solvents; a1.2) at least one catalytic material based on at least one metal of group VI B supported on an electroconductive support, in powder form, is added to the solution obtained in step a1.1); steps a1.1) and a1.2) being carried out in any order, or simultaneously; a2) the ink obtained in step a1) is deposited onto an electronically conductive membrane or collector.

[0079] The electrode obtained following steps a1) and a2) is then dried either in open air or under a controlled atmosphere (typically under nitrogen or argon) at a temperature between 5°C and 100°C, preferably between 15°C and 60°C and at a pressure between 0.0001 MPa and 0.1 MPa.

[0080] Step a1) Ink preparation

[0081] The binder

[0082] The binder is a polymer binder chosen for its ability to be deposited as a layer of variable thickness and for its ionic conductivity in aqueous media and its diffusion capacity for dissolved gases. The layer of variable thickness, advantageously between 1 and 500 µm, particularly between 10 and 100 µm, can be a gel or a film.

[0083] Advantageously, the ionically conductive polymer binder is:

[0084] *either a conductor of anionic groups, particularly hydroxyl groups, and is chosen from the group including, in particular:

[0085] - polymers stable in aqueous media, which may be perfluorinated, partially fluorinated or non-fluorinated and which have cationic groups allowing the conduction of hydroxide anions, said cationic groups being of the quaternary ammonium, guanidinium, imidazolium, phosphonium, pyridium or sulfide type;

[0086] - non-grafted polybenzimidazole;

[0087] - chitosan; and

[0088] - polymer mixtures comprising at least one of the different polymers mentioned above, said mixture having anionic conductive properties;

[0089] * either conducts cationic groups enabling the conduction of protons and is chosen from the group including in particular: - polymers stable in aqueous media, which may be perfluorinated, partially fluorinated or non-fluorinated and which have anionic groups enabling the conduction of protons;

[0090] - grafted polybenzimidazole;

[0091] - chitosan; and

[0092] - polymer mixtures comprising at least one of the different polymers mentioned above, said mixture having cationic conductivity properties.

[0093] Among the polymers that are stable in aqueous media and have cationic groups that allow the conduction of anions, we can notably mention perfluorinated polymer chains such as polytetrafluoroethylene (PTFE), partially fluorinated polymer chains such as polyvinylidene fluoride (PVDF) or non-fluorinated polymer chains such as polyethylene, which will be grafted with anionically conductive molecular groups.

[0094] Among the polymers stable in aqueous media and possessing anionic groups allowing proton conduction, we can consider any polymer chain stable in aqueous media containing groups such as -SOa', -COO', -POa2 ', -POsH', -CeFLO-. Examples include Nation®, sulfonated phosphon polybenzimidazole (PBI), and sulfonated or phosphon polyetheretherketone (PEEK).

[0095] According to the present invention, any mixture comprising at least two polymers, at least one of which is selected from the groups of polymers mentioned above, may be used, provided that the final mixture is ionically conductive in aqueous media. For example, a mixture comprising a polymer stable in alkaline media and having cationic groups enabling the conduction of hydroxide anions with polyethylene not grafted by anionically conductive molecular groups may be used, provided that this final mixture is anionically conductive in alkaline media. Another example is a mixture of a polymer stable in acidic or alkaline media and having anionic or cationic groups enabling the conduction of protons or hydroxides with polybenzimidazole, whether grafted or not.

[0096] Advantageously, polybenzimidazole (PBI) is used in the present invention as a binder. While not inherently a good ionic conductor, in alkaline or acidic media it proves to be an excellent polyelectrolyte with very good anionic and cationic conductivity, respectively. PBI is a polymer commonly used, in grafted form, in the manufacture of proton-conducting membranes for fuel cells, in membrane-electrode assemblies, and in PEM-type electrolyzers, as an alternative to Nation®. In these applications, PBI is generally functionalized / grafted, for example by sulfonation, to make it proton-conducting. The role of PBI in this type of system is therefore different from its role in the manufacture of electrodes according to the present invention, where it serves only as a binder and has no direct role in the electrochemical reaction.

[0097] Although its long-term stability in concentrated acidic media is limited, chitosan, which can also be used as an anionic or cationic conducting polymer, is a polysaccharide with ionic conduction properties in basic media that are similar to those of PBI (G. Couture, A. Alaaeddine, F. Boschet, B. Ameduri, Progress in Polymer Science 36 (2011) 1521-1557).

[0098] Advantageously, the electrode according to the invention is formulated by a process which further comprises a solvent removal step, either concurrently with or following the drying step. Solvent removal can be achieved by any technique known to those skilled in the art, in particular by evaporation or phase inversion.

[0099] In the case of evaporation, the solvent is an organic or inorganic solvent whose evaporation temperature is lower than the decomposition temperature of the polymer binder used. Examples include dimethyl sulfoxide (DMSO) and acetic acid. A person skilled in the art is capable of selecting the appropriate organic or inorganic solvent for the polymer or polymer blend used as a binder and capable of evaporating.

[0100] According to a preferred embodiment of the invention, the electrode is suitable for use for the electrolysis of water in an AEM electrolyzer and the polymer binder is then an anionic conductor in an alkaline electrolyte medium, in particular a conductor of hydroxides.

[0101] For the purposes of the present invention, an alkaline electrolyte medium is understood to be a medium whose pH is greater than 7, advantageously greater than 10.

[0102] The binder is advantageously conductive of hydroxides in alkaline media. It is chemically stable in electrolysis baths and has the capacity to diffuse and / or transport the OH- ions involved in the electrochemical reaction to the surface of the particles, the sites of the redox reactions that produce H2 and O2 gases. Thus, a surface that would not be in direct contact with the electrolyte is still involved in the electrolysis reaction, a key factor in the system's efficiency. The chosen binder and the electrode's shape do not impede the diffusion of the gases formed and limit their adsorption, thereby allowing their release. According to another preferred embodiment of the invention, the electrode is suitable for use in the electrolysis of water in a PEM electrolyzer, and the polymer binder is a cationic conductor in acidic electrolyte media, particularly a proton conductor.

[0103] For the purposes of the present invention, an acidic medium is understood to be a medium whose pH is less than 7, advantageously less than 2.

[0104] Solvent The solvent used in step a1.1) is a polar or nonpolar, protic or aprotic solvent, or a mixture of different solvents. Preferably, the solvent is a mixture of water and an alcohol comprising between 1 and 4 carbon atoms.

[0105] Catalytic material

[0106] For the purposes of this invention, catalytic material powder means a powder consisting of particles of micron, sub-micron, or nanometer size. The powders can be prepared using techniques known to those skilled in the art.

[0107] Preferably, the catalytic material is based on molybdenum sulfide and / or tungsten sulfide, and preferably, the catalytic material is based on molybdenum sulfide.

[0108] According to one or more embodiments, said catalytic material based on at least one metal from group VIB sulfide is doped with a doping element selected from boron, phosphorus and silicon, nickel, cobalt or iron, titanium, zirconium, or hafnium or added with organic compounds as described in patent application W02020 / 109065.

[0109] The catalytic material based on at least one metal from group VIB sulfide is in the supported state on an electroconductive support.

[0110] In a particular embodiment of the invention, said electro-conductive support is chosen from carbon structures such as carbon black, graphite, carbon nanotubes or graphene.

[0111] In a particular embodiment of the invention, said support comprises at least one electroconductive material selected from gold, copper, silver, titanium, silicon, fluorine-doped tin dioxide, and indium tin oxide.

[0112] A porous and non-electrically conductive material can be made electrically conductive by depositing an electrically conductive material on its surface; for example, a refractory oxide, such as alumina, within which graphitic carbon is deposited.

[0113] The catalytic material support advantageously has a specific surface area BET (SS) greater than 75 m² 2 / g, preferably greater than 100 m 2 / g, preferably above 130 m 2 / g.

[0114] The catalytic material support can be added during the preparation of the catalytic material and / or during the preparation of the electrode.

[0115] The solid catalytic material based on at least one metal from group VIB sulfide may come from a commercial source or be prepared by processes known from the prior art.

[0116] The deposition on an electro-conductive support of said catalytic material based on at least one metal of group VIB is carried out according to the following steps: 1) a step of bringing said electro-conductive support into contact with at least one solution containing at least one precursor of at least one metal of group VI B;

[0117] 2) optionally, a step of contacting the electro-conductive support with at least one solution containing at least one precursor of a dopant; steps 1) and 2), if both carried out, being carried out in any order or simultaneously and allowing the wet-supported impregnated catalytic material to be obtained;

[0118] 3) a heat treatment step of the wet-supported impregnated catalytic material obtained at the end of steps 1) and optionally 2) to obtain a dried catalytic material,

[0119] 4) a step of sulfidation of the dried catalytic material obtained at the end of step 3) to obtain said catalytic material based on at least one supported sulfide metal of group VI B.

[0120] Advantageously, the step of contacting the substrate with at least one precursor of at least one metal from Group VI B, in accordance with the implementation of step 1), can be carried out by impregnation, either dry or in excess, or by deposition-precipitation, according to methods well known to those skilled in the art. Preferably, said step 1) is carried out by dry impregnation, which consists of contacting the substrate with a solution containing at least one precursor of at least one metal from Group VI B, the volume of which is between 0.25 and 1.5 times the porous volume of the substrate to be impregnated.

[0121] According to one or more embodiments, said precursor of at least one metal from group VI B, added in step 1) is chosen from:

[0122] -polyoxometalates corresponding to the formula (HhX x M m Oy) q' in which H is hydrogen, X is an element chosen from phosphorus (P), silicon (Si), boron (B), said element being taken alone, M is one or more element(s) chosen from molybdenum (Mo), tungsten (W), O being oxygen, h being an integer between 0 and 12, x being an integer between 0 and 4, m being an integer equal to 5, 6, 7, 8, 9, 10, 11, 12 or 18, y being an integer between 17 and 72 and q being an integer between 1 and 20;

[0123] -precursor salts of elements in group VI B; and

[0124] -organic or inorganic precursors based on Mo or W.

[0125] The precursor of a dopant element used in optional step 2) is chosen from boron, phosphorus and silicon, nickel, cobalt or iron, titanium, zirconium, or hafnium.

[0126] Advantageously, organic additives are introduced into the impregnation solution during step 1) or 2) as described in application W02020 / 109065.

[0127] Step 3) of heat treatment is carried out at a temperature below 250°C, preferably below 180°C, and more preferably below 120°C. Most preferably, drying is carried out under reduced pressure at a temperature not exceeding 80°C. The drying time is between 30 minutes and 24 hours, preferably between 30 minutes and 16 hours. Preferably, the drying time does not exceed 4 hours.

[0128] The drying stage can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or under an atmosphere containing oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure.

[0129] Step 4) of sulfidation is intended to sulfide at least partially the metal of group VI B. It can advantageously be carried out using a gaseous mixture of H2S / H2 or H2S / N2 containing at least 5% vol. of H2S in the mixture or under a flow of pure H2S at a temperature between 100°C and 600°C, under a total pressure equal to or greater than 0.1 MPa for at least 2 hours.

[0130] The Group VI B metal content in the catalytic material is between 4 and 60% by weight of the metal element relative to the weight of the final catalytic material, and preferably between 7 and 50% by weight relative to the weight of the catalytic material. Furthermore, the surface density, which corresponds to the quantity of Group VI B metal atoms deposited per unit area of ​​support, is advantageously between 0.5 and 20 metal atoms per square nanometer of support, and preferably between 2 and 15 metal atoms per square nanometer of support.

[0131] In a particular embodiment of the invention, an electro-conductive support is added to the ink in step a1) in addition to that present in the supported catalytic material.

[0132] A person skilled in the art, drawing on their general knowledge, will be able to determine the quantities of each component of the electrode. The density of catalytic material particles must be sufficient to reach their electrical percolation threshold.

[0133] According to a preferred embodiment of the invention, the polymer binder / catalytic material mass ratio is between 5 / 95 and 95 / 5, preferably between 10 / 90 and 90 / 10, and more preferably between 10 / 90 and 40 / 60.

[0134] Step a2) Deposition of ink onto a membrane, or an electronically conductive collector.

[0135] In one embodiment according to the invention, the ink obtained in step a1) is deposited on a membrane, preferably a proton exchange or anion exchange membrane.

[0136] For the purposes of this invention, a proton exchange membrane is defined as a semi-permeable, extremely thin membrane (between 20 and 300 micrometers) made from ionomers that allows proton conduction while remaining impermeable to gases such as oxygen or hydrogen: protons pass through the membrane while gases are blocked. This characteristic is exploited in the Membrane-Electrode Assemblies (MEAs) of PEM electrolyzers. PEMs are made from pure polymer membranes or composite membranes where the materials form a polymer matrix. They are almost exclusively composed of acid perfluorosulfonated membranes (PFSAs), the best-known of which is Nation® from DuPont de Nemours. Nation® is an ionomer composed of a hydrophobic poly(tetrafluoroethylene) (PTFE) backbone onto which are grafted perfluoroethylene (perfluorovinyl ether) pendant chains terminated by sulfonic groups.

[0137] An anion exchange membrane is defined as a semi-permeable, extremely thin membrane (between 20 and 300 micrometers) made from ionomers that allows the conduction of hydroxyl (or hydroxide) anions while remaining impermeable to gases such as oxygen or hydrogen: OH- ions pass through the membrane while gases are blocked. This characteristic is exploited in the Membrane-Electrode Assembly (MEA) of electrolyzers.

[0138] In another embodiment, the ink obtained in step a1) is deposited onto a current collector. For the purposes of this invention, a current collector is understood to be any conductive material having the same conductive properties as metals, for example, graphite or certain conductive polymers such as polyaniline and polythiophene. This support can have any shape that allows the resulting mixture (between the binder and the catalytic material) to be deposited by a method selected from the group including, in particular, dipping, printing, induction, pressing, coating, spin coating, filtration, vacuum deposition, spray deposition, casting, extrusion, or lamination. The support or collector can be solid or perforated.Examples of supports include a grid (openwork support), a plate or sheet of stainless steel (304L or 316L for example) (solid supports).

[0139] The advantage of the ink according to the invention is that it can be deposited on a solid or perforated collector, by usual deposition techniques which are easily accessible and allow deposition in the form of layers of varying thicknesses ideally on the order of 10 to 100 pm.

[0140] According to the invention, the ink can be prepared by any technique known to those skilled in the art, in particular by mixing the binder and at least one catalytic material in powder form with a suitable solvent or a mixture of suitable solvents to obtain a mixture with rheological properties that allow the electrode materials to be deposited as a film of controlled thickness onto an electronically conductive substrate. The use of the catalytic material in powder form maximizes the surface area of ​​the electrodes and enhances their associated performance. Those skilled in the art will be able to select the various formulation parameters based on their general knowledge and the physicochemical characteristics of the mixtures.

[0141] Step b) Electrochemical activation of the electrode

[0142] According to step b) of the preparation process according to the invention, an oxidative electrochemical treatment of the electrode supplied in step a) is carried out by cyclic voltammetry (CV) or chronoamperometry (CA) to obtain an electrochemically activated electrode, said treatment being characterized by the use of an oxidation potential applied to the electrode between 0 V vs ENH and 2.5 V vs ENH.

[0143] Cyclic voltammetry (CV) involves sweeping a working electrode relative to a reference electrode between an initial potential and maximum and minimum potentials, and measuring the current. A positive current is conventionally considered an oxidation current, and a negative current, a reduction current. The sweep cycle can be repeated several times. The CV sweep rate is preferably between 1 and 100 mV / s. 1 The number of CV cycles is preferably between 1 and 100.

[0144] Chronoamperometry (CA) is an electrochemical technique that involves applying a potential to a working electrode relative to a reference electrode and measuring the change in current over time. CA measurements are preferably performed for a duration between 1 and 600 minutes, and more preferably between 30 and 300 minutes.

[0145] The said electrochemical treatment is advantageously carried out in the presence of an aqueous solution containing deionized water whose pH is controlled or in contact with a hydrated membrane.

[0146] According to one or more embodiments, the temperature of the electrochemical treatment is between 0°C and 80°C, and preferably between 20°C and 60°C.

[0147] Preferably, the oxidation potential of each CV or CA applied to the electrode during the oxidative electrochemical treatment step is between 0.5 V vs ENH and 1.3 V vs ENH.

[0148] According to one or more embodiments, the oxidative electrochemical treatment step can be carried out several times successively, from 1 to 10 times, preferably from 1 to 5 times. Increasing potentials are advantageously used during the different stages of the oxidative electrochemical treatment.

[0149] In one or more particular embodiments of the invention, at least one reductive electrochemical treatment step by cyclic voltammetry (CV) or chronoamperometry (CA) is carried out between steps a) and b). This reductive electrochemical treatment step is characterized by the use of a reduction potential applied to the electrode ranging from 0 V vs EN H to -2 V vs EN H.

[0150] Preferably, the reduction potential of each CV or CA applied to the electrode during the reductive electrochemical treatment step is between -0.25 V vs ENH and -2 V vs ENH.

[0151] According to one or more embodiments, the reductive electrochemical treatment step can be carried out between 1 and 10 times, preferably between 1 and 5 times. Decreasing potentials are advantageously used during the different stages of the reductive electrochemical treatment.

[0152] Usage methods

[0153] Another object according to the invention relates to an electrolysis device comprising an anode, a cathode, an electrolyte, in which at least one of the anode or the cathode is an electrode according to the invention.

[0154] The electrolysis device can be used as a water electrolysis device for the production of a gaseous mixture of hydrogen and oxygen and / or the production of hydrogen alone, comprising an anode, a cathode, and an electrolyte. The device is characterized in that at least one of the cathode or anode is an electrode according to the invention, preferably the cathode. The electrolysis device consists of two electrodes (an anode and a cathode, which are electronic conductors) connected to a direct current generator and separated by an electrolyte (an ionically conductive medium). The anode is the site of water oxidation. The cathode is the site of hydrogen formation.

[0155] The electrolyte is a proton exchange polymer membrane H + or OH' anions which ensures the transfer of protons H +or OH' anions from the anode to the cathode or from the cathode to the anode respectively and allows the separation of the anodic and cathodic compartments, which avoids re-oxidizing at the anode the species reduced at the cathode and vice versa;

[0156] The minimum water supply for an electrolysis device is 0.8 l / Nm 3 of hydrogen. In practice, the actual value is close to 1 l / Nm 3 The water introduced must be as pure as possible because impurities remain in the equipment and accumulate during electrolysis, ultimately disrupting the electrolytic reactions by:

[0157] - the formation of sludge; and by - the action of chlorides on the electrodes.

[0158] An important specification for water relates to its ionic conductivity (which must be less than a few pS / cm).

[0159] There are many suppliers offering highly diversified technologies, particularly in terms of the nature of the electrolyte and associated technology, ranging from possible upstream coupling with a renewable power supply (photovoltaic or wind), to the direct final supply of pressurized hydrogen.

[0160] The electrolysis device can be used as a nitrogen electrolysis device for the production of ammonia, comprising an anode, a cathode and an electrolyte, said device being characterized in that at least one of the cathode or anode is an electrode according to the invention, preferably the cathode.

[0161] The electrolysis unit consists of two electrodes (an anode and a cathode, both electronic conductors) connected to a direct current generator and separated by an electrolyte (an ionically conductive medium). The anode is where water is oxidized. The cathode is where nitrogen is reduced and ammonia is formed. Nitrogen is continuously injected into the cathode compartment.

[0162] The nitrogen reduction reaction is:

[0163] N2+ 6H + +6 e - ^ 2NH3

[0164] The electrolyte can be:

[0165] - either an aqueous solution (Na2SC>4 or HCl), preferably saturated with nitrogen;

[0166] - either a proton exchange polymer membrane which ensures the transfer of protons from the anode to the cathode and allows the separation of the anodic and cathodic compartments, which avoids re-oxidizing at the anode the species reduced at the cathode and vice versa.

[0167] The electrolysis device can be used as a carbon dioxide electrolysis device for the production of formic acid, comprising an anode, a cathode, and an electrolyte, said device being characterized in that at least one of the cathode or the anode is an electrode according to the invention. An example of an anode and electrolyte that can be used in such a device is described in detail in document FR3007427.

[0168] The electrolysis device can be used as a fuel cell device for the production of electricity from hydrogen and oxygen comprising an anode, a cathode and an electrolyte (liquid or solid), said device being characterized in that at least one of the cathode or anode is an electrode according to the invention.

[0169] The fuel cell device consists of two electrodes (an anode and a cathode, both electronic conductors) connected to a load C to deliver the generated electric current, and separated by an electrolyte (an ionically conductive medium). The anode is where hydrogen oxidation takes place. The cathode is where oxygen reduction takes place.

[0170] The electrolyte can be:

[0171] - either an acidic aqueous solution (H2SO4 or HCl) or a basic one (KOH);

[0172] - either a polymer membrane exchanging protons or OH- anions which ensures the transfer of protons or OH- anions from the anode to the cathode or from the cathode to the anode respectively and allows the separation of the anodic and cathodic compartments, which avoids reoxidizing at the anode the species reduced at the cathode and vice versa.

[0173] The following examples illustrate the present invention without, however, limiting its scope. The examples below relate to the electrolysis of water in a liquid electrolytic medium for the production of hydrogen.

[0174] Examples

[0175] Example 1: Supply of a catalytic material S1 based on molybdenum sulfide in bulk form: commercial bulk M0S2

[0176] A first solid material S1 based on commercial molybdenum sulfide (supplier Sigma Aldrich; CAS number: 1317-33-5), in which the particles have an average size of 90 nm, is supplied in bulk form. The Mo content of the solid sulfide material is 100% by weight relative to the total weight of said solid material.

[0177] Example 2: Supply of a catalytic material S2 based on molybdenum sulfide and supported on an electrically conductive support: preparation of the M0S2 material supported on carbon black (30 wt% Mo)

[0178] A second solid material S2 based on molybdenum sulfide supported on commercial Ketjenblack ec-660jd type carbon black (supplier Nouryon; CAS number: 1333-86-4) with a specific surface area of ​​1380 m² 2 / g is prepared. To do this, 5.20 g of H3Mo2O4O, 28H2O are dissolved in 18.5 mL of water. The resulting solution is used to impregnate 3 g of carbon black. The resulting wet material is then dried in an oven at 120°C for 2 h. The dry material is then sulfided under pure H2S at 300°C for 2 h. The Mo content in the sulfided solid material is 30 wt% relative to the total weight of said solid material. The molybdenum density per square nanometer of carbon black is 4 at Mo / nm 2Example 3: Preparation of a working electrode E1 based on a catalytic material S1 (non-compliant)

[0179] To deposit the catalytic material S1 onto an electrode, an ink is formulated. For this purpose, 50 mg of catalytic material S1, to which 5 mg of acetylene black have been added to ensure electronic conductivity and 5 mg of polyvinylene fluoride (PVDF) to ensure mechanical adhesion of the ink deposit to the working electrode surface, are dispersed in 10 mL of a 4:1 water / ethanol mixture and then heated ultrasonically for 30 minutes to form the ink. A 10 µL deposit of ink is made on the glassy carbon tip of the rotating working electrode. After the ink has been deposited on the working electrode, the electrode is dried to evaporate the solvent at 20°C in open air to obtain the working electrode E1.

[0180] Example 4: Preparation of a working electrode E2 based on a catalytic material S2 (non-compliant)

[0181] To deposit the S2 catalytic material onto an electrode, an ink is formulated. For this purpose, 19 mg of S2 catalytic material were added to 80 pL of Nation® (a 20:80 H2O / Propanol solution at 5 wt% Nation®), which ensures the mechanical adhesion of the deposit to the electrode surface. This mixture was dispersed in 523 pL of isopropanol and 2.8 mL of ultrapure water. Two mg of commercial Ketjenblack carbon (supplier Nouryon; CAS number: 1333-86-4) were added to the mixture to ensure electronic conductivity. The mixture was then ultrasonically heated for 30 minutes. A 10 pL deposit of ink was applied to the vitreous carbon tip of the rotating working electrode. The electrode is dried to evaporate the solvent at a temperature of 20°C and in open air to obtain the working electrode E2.

[0182] Example 5: Preparation of an electrochemically activated working electrode A1-1: reductive electrochemical treatment of the working electrode E1 with a CA at -0.256 V vs EN H for 4 h (non-compliant)

[0183] The working electrode E1, prepared from bulk M0S2 according to Example 4, is electrochemically treated by chronoamperometry. In this example, only a reductive electrochemical treatment is carried out with a reduction potential of -0.256 V vs ENH for 4 h. No oxidative electrochemical treatment by applying an oxidation potential is performed. During this treatment, the electrode is immersed in a 0.5 M aqueous H2SO4 solution at 20 °C, deaerated by bubbling with N2. The electrode is rotated at a speed of 3000 rpm. Once this step is completed, the activated electrode A1-1 is obtained.

[0184] Example 6: Preparation of an electrochemically activated working electrode A1-2: oxidative electrochemical treatment of working electrode A1-1 with an AC at 0.194 V vs ENH for 4 h, an AC at 0.344 V vs ENH for 4 h and an AC at 0.744 V vs ENH for 1 h (non-compliant).

[0185] The working electrode A1-1 (prepared from bulk MoS2), having undergone a reductive electrochemical treatment as described in Example 5, is electrochemically treated by chronoamperometry. In this example, three oxidative electrochemical treatment steps are carried out successively: first, at an oxidation potential of 0.194 V vs ENH for 4 h, then at 0.344 V vs ENH for 4 h, and finally at 0.744 V vs ENH for 1 h. During this treatment, the electrode is immersed in a 0.5 M aqueous H2SO4 solution at 20 °C, deaerated by bubbling with N2. The electrode is rotated at a speed of 3000 rpm. Once this step is completed, the activated electrode A1-2 is obtained.

[0186] Example 7: Preparation of an electrochemically activated working electrode A2-1: reductive electrochemical treatment of the working electrode E2 with a CA at -0.256 V vs ENH for 4 h (non-compliant)

[0187] The working electrode E2, prepared from supported M0S2 (30 wt% Mo) according to Example 4, is electrochemically treated by chronoamperometry. In this example, only a reductive electrochemical treatment step is performed with a reduction potential of -0.256 V vs. ENH for 4 h. No oxidative electrochemical treatment by applying an oxidation potential is carried out. During this treatment, the electrode is immersed in a 0.5 M aqueous H2SO4 solution at 20 °C, deaerated by bubbling with N2. The electrode is rotated at a speed of 3000 rpm. Once this step is completed, the activated electrode A2-1 is obtained.

[0188] Example 8: Preparation of an electrochemically activated working electrode A2-2: Oxidative electrochemical treatment of working electrode A2-1 with an oxidation potential of 0.194 V vs ENH for 4 h, an oxidation potential of 0.344 V vs ENH for 4 h, and an oxidation potential of 0.744 V vs ENH for 1 h (compliant). Working electrode A2-1 (prepared from M0S2 supported at 30 wt% Mo), having undergone a reductive electrochemical treatment step as described in Example 7, is electrochemically treated by chronoamperometry. In this example, three oxidative electrochemical treatment steps are carried out successively with an oxidation potential of 0.194 V vs ENH for 4 h, followed by a potential of 0.344 V vs ENH for 4 h, and then a potential of 0.744 V vs ENH for 1 h. During this treatment, the electrode is immersed in a 0.5 M aqueous H2SO4 solution at 20 °C, deaerated by bubbling with N2. The electrode is rotated at a speed of 3000 rpm.Once this step is completed, the activated electrode A2-2 is obtained.

[0189] Example 9: Preparation of an electrochemically activated working electrode A2-3: oxidative electrochemical treatment of the working electrode A2-2 with a CA at 1.24 V vs ENH for 4 h (compliant).

[0190] The working electrode A2-2 (prepared from M0S2 supported at 30 wt% Mo) has undergone a reductive electrochemical treatment as described in Example 7, followed by three oxidative electrochemical treatment steps as described in Example 8. It is then electrochemically treated by chronoamperometry. In this example, one oxidative treatment step is carried out with an oxidation potential of 1.24 V vs. ENH for 4 h. During this treatment, the electrode is immersed in a 0.5 M aqueous H2SO4 solution at 20 °C, deaerated by bubbling with N2. The electrode is rotated at a speed of 3000 rpm. Once this step is completed, the activated electrode A2-3 is obtained.

[0191] Example 10: Electrochemical tests of working electrodes

[0192] The catalytic activity of catalytic materials is characterized in a three-electrode cell. This cell consists of a working electrode, a platinum counter electrode, and an Ag / AgCl reference electrode. The electrolyte is a 0.5 mol / L aqueous solution of sulfuric acid (H₂SO₄). This medium is deoxygenated by bubbling with nitrogen, and measurements are performed under an inert atmosphere (nitrogen deaeration).

[0193] The working electrode consists of a 5 mm diameter glassy carbon disc set in a Teflon tip (rotating disc electrode). Glassy carbon has the advantage of having no catalytic activity and being a very good electrical conductor.

[0194] The performance of the electrochemically unactivated working electrodes E1, E2, prepared as described in examples 3 and 4, and of the electrochemically activated electrodes A1-1, A1-2, A2-1, A2-2, A2-3 prepared as described in examples

[0195] 5 to 9 are tested.

[0196] Various electrochemical methods are used to determine the performance of catalysts:

[0197] - Linear voltammetry: This involves applying a time-varying potential signal to the working electrode, from 0 to -0.5 V vs. ENH (Normal Hydrogen Electrode, according to Anglo-Saxon terminology), at a rate of 2 mV / s, and measuring the faradaic response current, i.e., the current due to the redox reaction occurring at the working electrode. This method is ideal for determining the catalytic power of a material for a given reaction. Among other things, it allows for the determination of the overpotential required for the reduction of protons to H2.

[0198] It also allows us to determine the value of the Tafel slope, which provides information on the kinetic aspect of the electrochemical reaction. The Tafel equation is an electrochemical kinetic equation that relates the overpotential to the rate of the electrochemical reaction, itself represented by the current density:

[0199] The sign is positive for an anodic reaction and negative for a cathodic reaction.

[0200] With :

[0201] A: Tafel slope in volts per decade (V / dec) rj: overvoltage in volts (V) i: current density in amperes (A) io: exchange current density in amperes per cm 2 of the electrode. The term io represents the rate of electron transfer between the electrode and the electrolyte. For example, in the case of HER at 1 mol / kg of SCU, io is equal to -log 3.1. For tungsten, io is -log 5.9. For palladium, which has the highest rate, io is equal to -log 3.03.

[0202] Note that the lower the absolute value of the Tafel slope, the faster the reaction kinetics. Recall that in the case of platinum, the overpotential is -10 mA / cm². -2The potential difference is between -15 and -40 mV depending on the type of electrocatalyst used (based on the Pt / C ratio), and the Tafel slope is approximately 23 mV / dec vs. 95 mV / dec for a bulk M0S2. Chronopotentiometry, on the other hand, consists of applying a current or current density for a specific time and measuring the resulting potential. This study allows for the determination of catalytic activity at constant current as well as the stability of the system over time. It is performed with a current density of -10 mA / cm². 2 and for a given period of time.

[0203] The electrochemical performance of the working electrodes is summarized in Table 1 below. It is expressed as overpotential at a current density of -10 mA / cm². 2 and in Tafel slope (mV / dec).

[0204] These results are also compared to performance results of catalytic materials disclosed in the prior art:

[0205] - Massive M0S2 disclosed by LX Chen, et al. “Design of Dual-Modified MoS2 with Nanoporous Ni and Graphene as Efficient Catalysts for the Hydrogen Evolution Reaction”, 2018.

[0206] - M0S2 film on titanium substrate before and after two 12h pretreatment cycles at -10 mA. cm' 2 followed by a CV between -0.25 and 0.85 V vs. ENH disclosed by P. Gaigalas, "The enhancement of hydrogen evolution reaction on nanoplatelet-shaped MoS2 via anodic pretreatment," 2024. In this article, MoS2 is deposited as a film on TiU2 nanotubes, which are themselves deposited on a titanium sheet. MoS2 is not dispersed as nanoparticles as in the present invention, and in particular as in Example 2, where MoS2 is dispersed on a carbon support by impregnation such that the molybdenum density per square nanometer of carbon black is 4 at Mo / nm 2 .

[0207] Table 1

[0208] These examples demonstrate the advantages of electrochemically treating a carbon-supported M0S2 catalyst with a reductive (A1-1 and A1-2) and then oxidative treatment for HER reactions in acidic media. Electrochemical treatment of bulk M0S2 or M0S2 deposited on a titanium substrate provides a performance gain, but it is too small to match the performance of an electrochemically treated or untreated carbon-supported M0S2. Indeed, depending on the electrochemical treatment, the measured overpotentials range from 292 mV (E1), 282 mV (LX Chen, et al., 2018), or 246 mV (P. Gaigalas, et al., 2024) to 232 mV (P. Gaigalas, et al., 2024) or 254 mV A1-2 (non-compliant), compared to overpotentials of 237 mV (E2) for untreated M0S2 / C. A purely reductional treatment only reduces the overvoltages to 199 mV (A2-1).

[0209] Oxidative treatment significantly reduces these overvoltages. With a maximum treatment potential of 0.744 V vs. ENH for one hour, the potential of electrode A2-2 is reduced to 109 mV. However, the most significant effects are achieved by increasing the treatment potential. After several hours at various potentials, the highest being 1.244 V vs. ENH, the overvoltages are reduced to -10 mA / cm². 2 drop to 68 mV (A2-3).

Claims

DEMANDS 1. A process for preparing an electrochemically activated electrode for electrochemical reduction reactions, said electrode comprising at least one catalytic material based on at least one metal of group VI B supported on an electroconductive support, said process comprising at least the following steps: a) supplying an electrode comprising at least one catalytic material based on at least one metal of group VIB supported on an electroconductive support; b) carrying out an electrochemical oxidative treatment of the electrode supplied in step a) by cyclic voltammetry (CV) or chronoamperometry (CA) to obtain an electrochemically activated electrode, said treatment being characterized by the use of an oxidation potential applied to the electrode of between 0 V vs ENH and 2.5 V vs ENH.

2. A method according to claim 1, wherein between step a) and step b) a reductive electrochemical treatment step is carried out, characterized by the use of a reduction potential applied to the electrode between -0.25 V vs ENH and -2 V vs ENH.

3. A process according to claim 1 or 2, wherein the oxidative electrochemical treatment of step b) is characterized by the use of an oxidation potential applied to the electrode of between 0.5 V vs ENH and 1.3 V vs ENH.

4. A process according to any one of claims 1 to 3, wherein the oxidative electrochemical treatment of step b) is carried out between 1 and 5 times successively with increasing oxidizing potentials.

5. A method according to any one of the preceding claims, wherein the scan rate used in the cyclic voltammetry oxidative electrochemical treatment of step b) is between 1 mV.s' 1 and 100 mV.s'1 .

6. A method according to any one of the preceding claims, wherein the number of cycles used in the cyclic voltammetry oxidative electrochemical treatment of step b) is between 1 and 100.

7. A process according to any one of the preceding claims, wherein the duration of the oxidative electrochemical treatment by chronoamperometry in step b) is between 1 minute and 600 minutes.

8. A method according to any one of the preceding claims, wherein the duration of the oxidative electrochemical treatment by chronoamperometry in step b) is between 30 minutes and 300 minutes.

9. A method according to the preceding claim, wherein in step a) said group VI B metal is molybdenum.

10. A method according to any one of the preceding claims, wherein in step a) the electro-conductive support is carbon.

11. A method according to any one of the preceding claims, wherein in step a) the content of group VI B metal in the catalytic material is between 4 and 60% by weight relative to the total weight of the catalytic material.

12. A method according to any one of the preceding claims, wherein in step a) the surface density which corresponds to the quantity of group VI B metal atoms deposited per unit surface area of ​​support is between 0.5 and 20 atoms of metallic element per square nanometer of support.

13. Electrolysis device comprising an anode, a cathode, an electrolyte, said device being characterized in that at least one of the anode or cathode is an electrode prepared according to one of claims 1 to 12.

14. Use of the electrolysis device according to claim 13 in electrochemical reactions.

15. Use according to claim 14, wherein said device is used as: - water electrolysis device for the production of a gaseous mixture of hydrogen and oxygen and / or the production of hydrogen alone; - nitrogen electrolysis device for the production of ammonia; - carbon dioxide electrolysis device for the production of formic acid, CO and ethylene; - fuel cell device for the production of electricity from hydrogen and oxygen.

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