Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/042—Electrodes formed of a single material
  • C25B11/047—Ceramics
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/50—Processes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/042—Electrodes formed of a single material
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B5/00—Electrogenerative processes, i.e. processes for producing compounds in which electricity is generated simultaneously
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
  • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
  • H01M8/065—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants by dissolution of metals or alloys; by dehydriding metallic substances
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0002—Aqueous electrolytes
  • H01M2300/0005—Acid electrolytes
  • H01M2300/0011—Sulfuric acid-based
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

• the present invention relates to a process for generating hydrogen by electrolysis of water.
• Conventional water electrolysis consists of breaking it down into hydrogen and oxygen (gas) under the influence of an applied electrical potential. Typically two moles of hydrogen and one mole of oxygen are generated per mole of water consumed. Within the electrolyser, hydrogen is produced at the cathode (negative electrode) while oxygen is simultaneously generated at the anode (positive electrode). These are referred to as hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) respectively.
• HER hydrogen evolution reaction
• OER oxygen evolution reaction
• the high-temperature technology (less mature) is based on a ceramic that conducts O 2- ions at high temperature (>500°C°) used as a separating membrane/electrolyte.
• PEM-type electrolysers which operate in a concentrated proton medium make it possible to achieve current densities of the order of 1 to 2 A/cm 2 , much higher than the current densities displayed by alkaline electrolysers. They also have a much higher response dynamics.
• the stability of materials is obviously put to the test in acidic environments, which requires the use of noble materials/metals.
• Catalysts are expensive, typically platinum (Pt) is used at the cathode (HER) and iridium oxide (Ir02) at the anode (OER).
• Catalysts in an alkaline medium are generally Nickel alloys which remain less expensive and have good stability. The simultaneous generation of gases (oxygen and hydrogen) within the electrolyser presents certain limits.
• the rate of the hydrogen evolution reaction is necessarily dependent on the very slow kinetics of the oxygen evolution reaction (OER), which requires imposing a significant overvoltage on the electrochemical cell, and therefore reduces the energy efficiency of electrolysis.
• PEM systems make it possible to manage pressure differences between compartments, which is not possible with alkaline systems which need to be at isopressure within the cathodic and anodic compartments.
• gas crossover The diffusion of gases through the membrane (“gas crossover”) remains problematic for optimum efficiency and is all the more important during slow operating regimes. Such gas mixtures then require post-purification of the hydrogen.
• An approach to avoid this type of scenario may consist in carrying out an electrolysis of water in a decoupled way, namely to produce a release of hydrogen and oxygen shifted in time and/or in space.
• hydrogen and oxygen are not produced simultaneously within the system, which definitely avoids the potential mixing of gases. Consequently, this approach makes it possible to consider more secure and potentially less expensive system architectures.
• Redox mediators were notably initiated by Cronin et al. (Nat. Chem. 2013, 5, 403-409) which makes it possible to decouple the electrolysis of water in 2 stages under polarization.
• the redox mediator for example phosphomolybdic acid (H3O+) [H2PMo12O40]
• H3O+ phosphomolybdic acid
• H2PMo12O40 H2PMo12O40
• Yonggang et al. (Fudan University) describe an electrolyzer in alkaline medium with 3 electrodes, namely a catalytic electrode of the HER, a catalytic electrode of the OER and an intermediate electrode of Ni(OH)2, which thus makes it possible to generate hydrogen by electrolysis of water in 2 stages of successive polarization.
• the Ni(OH)2 electrode has a redox potential certainly higher than that of oxidation of water, but the reaction kinetics of the latter is so slow that the oxidation of Ni(OH)2 takes place preferentially.
• the system composed of the HER and the Ni(OH)2 electrode is charged: the water molecules are electrochemically reduced to hydrogen at the HER cathode while the nickel hydroxide electrode (Ni(OH)2) is oxidized to nickel oxyhydroxide (NiOOH).
• the system composed of the NiOOH electrode and the OER electrode is then polarized.
• the negative electrode of NiOOH is electrochemically reduced back to its initial state of Ni(OH)2 while the hydroxide ions oxidize to oxygen at the positive electrode.
• This system therefore makes it possible to produce hydrogen and oxygen in a time-shifted manner without requiring the use of a particular diaphragm.
• the system finally requires a global potential of charge following the 2 polarizations higher than the potential of a traditional electrolysis. Regeneration of Ni(OH)2 will require subjecting a significant overvoltage to the OER electrode.
• This application describes thermal regeneration of the NiOOH electrode.
• the NiOOH electrode is reduced by water to Ni(OH)2.
• the system can then be charged again and produce hydrogen.
• this approach nevertheless requires the presence of a hot source that does not require the use of additional electrical power: which means installation in an adequate area, which can be limiting.
• Another approach described in WO2019/193283 consists in implementing an electrochemical process for the production of gaseous hydrogen by electrolysis then electrochemical conversion of H+ ions into gaseous hydrogen, either by depolarization with production of electrical energy (battery), or by catalytic route.
• the method essentially consists in implementing, in a decoupled manner, a step of electrolysis of an electrolyte producing gaseous oxygen and a stage of electrochemical conversion of H+ ions into gaseous hydrogen in an enclosure which contains a liquid phase and a gaseous phase not dissolved in this liquid phase.
• Such a method uses three electrodes.
• the object of the invention is in particular to solve the technical problem of providing a device and method for the decoupled electrolysis of water.
• the object of the invention is in particular to solve the technical problem of providing a device and method for producing hydrogen and oxygen.
• the aim of the invention is to solve these technical problems with a good conversion efficiency in the production of hydrogen and/or oxygen, and preferably while ensuring good safety of the whole.
• the present invention particularly aims to solve the technical problem of simplifying and optimizing prior systems.
• the invention consists in producing hydrogen (H2, typically in gaseous form) under pressure via a decoupled electrolysis process, i.e. a production of hydrogen and oxygen which is not simultaneous, in order to promote safety of the system with good conversion efficiency.
• the invention relates to a process for generating hydrogen by electrolysis of water, characterized in that it uses an electrochemical device 1 comprising only two electrodes 10, 20, namely a positive electrode 20 based on a catalyst bifunctional forming successively an oxygen evolution reaction electrode 20a (OER) and a hydrogen evolution reaction electrode 20b (HER), depending on whether the device 1 is subjected to an electric charge or delivers an electric charge, and a negative electrode 10 implementing a redox couple M m+ /M, where M represents a metallic element in reduced form (metal) and M m+ represents this metallic element in oxidized form (metallic ions), said electrodes 10 , 20 immersing in a aqueous electrolyte 50, said method comprising at least: a step of electrolysis under polarization (charge) inducing, at the negative electrode 10, a reduction of the metallic element in oxidized form M m+ into a red metallic element uit M in solid form, the metal having an H 2 overvoltage, and inducing the generation of
• the invention also relates to a device 1 for implementing the method according to the invention comprising:
• At least one closed enclosure intended to contain at least one aqueous electrolyte
• At least one positive electrode 20 capable of forming an OER 20a and HER 20b electrode intended to be immersed in the electrolyte 50;
• At least one negative electrode 10 forming a redox electrode intended to be immersed in the electrolyte 50;
• an electric circuit 30, 40 making it possible to manage the charging (electrolysis step) and discharging (conversion step) of the device 1, capable of successively operating the positive electrode as OER electrode 20a and HER electrode 20b;
• HER electrode when G positive electrode forms or functions as HER electrode and of “OER electrode” when the positive electrode forms or functions as OER electrode.
• redox electrode for the second electrode (negative electrode).
• aqueous electrolyte denotes an aqueous solution, therefore containing H + protons and/or OH ⁇ hydroxide ions, and optionally M m + ions.
• the term "acid electrolyte” designates an electrolyte having a pH ⁇ 7 (+/- 0.1).
• basic electrolyte designates an electrolyte having a pH > 7 (+/- 0.1).
• the invention implements a metallic element M blocking the release of hydrogen when its oxidized form M m+ is reduced. This is the phenomenon called hydrogen overvoltage, leading to a non-equilibrium electrochemical state which prevents the evolution of hydrogen during a polarization inducing the reduction of M m+ .
• the electrolysis step induces, concomitantly with the reduction of M m+ to M, a release of oxygen at the OER electrode.
• the conversion step induces, concomitantly with the oxidation of M to M m+ , a release of hydrogen at the HER electrode.
• the reduced metallic element M in solid form forms a deposit on the negative electrode.
• a voltage or bias is applied between the redox electrode and the OER electrode.
• the OER electrode is connected to the positive pole of a generator and the redox electrode is connected to the negative pole of the generator.
• the conversion step by spontaneous reaction generates an electrical voltage, giving rise to useful electrical energy.
• a voltage is generated between the redox electrode and the HER electrode.
• the voltage between the HER electrode and the redox electrode can supply an external electrical circuit, and can advantageously be stored in the form of electrical energy or a converted form of the electrical energy generated. This then promotes the energy efficiency (yield) of the entire process.
• the invention provides a process for the decoupled electrolysis of water within an electrolyser with 2 electrodes including a catalytic electrode operating successively as an evolution electrode of hydrogen (HER) and oxygen (OER) associated to a second electrode forming a redox electrode (M m+ /M) exhibiting a hydrogen overvoltage and capable of being reduced in the form of metal.
• a catalytic electrode operating successively as an evolution electrode of hydrogen (HER) and oxygen (OER) associated to a second electrode forming a redox electrode (M m+ /M) exhibiting a hydrogen overvoltage and capable of being reduced in the form of metal.
• HER evolution electrode of hydrogen
• OER oxygen
• the electrolysis step comprises a polarization step (charge) between the redox electrode in the oxidized state (negative electrode) and the OER electrode (positive electrode) immersed in the aqueous electrolyte.
• a polarization step charge between the redox electrode in the oxidized state (negative electrode) and the OER electrode (positive electrode) immersed in the aqueous electrolyte.
• the polarization is stopped.
• the metal M resulting from the reduction of the redox electrode M m + has a hydrogen overvoltage, which means that it can be deposited on a substrate from M m + ions while avoiding the gas evolution and that it is not reactive towards protons for kinetic reasons.
• the hydrogen overvoltage is ultimately of kinetic origin. This can be very slow on some substrates.
• the overvoltage thus corresponds to an additional potential necessary beyond the thermodynamic prerequisites for the reaction to take place at a given rate (Electrochemical Methods, Fundamentals and Applications, Allen J. bard, Larry R. Faulkner, John Wiley & Sons, 2001).
• the metal M is chosen so that it can form in solid form during charging (cathodic reduction) with the best possible yield.
• the absolute value of the overvoltage of the hydrogen evolution reaction on the metal M is greater than the difference E 0 (H + /H2) - E°(M m+ /M) in an acid medium and the difference E ⁇ PhO/Ph) - E°(M m+ /M) in basic medium, where E° is the standard redox potential.
• thermodynamically conceivable but kinetically blocked reaction between the metal and the protons becomes possible by coupling the metal electrode with an electrode catalyzing the proton reduction reaction.
• the association of these 2 electrodes is a fundamental aspect of the invention, since this makes possible the spontaneous reaction, in other words the generation of both hydrogen and an electrical voltage.
• the decomposition of water in two stages first allows the generation of oxygen during polarization and then the spontaneous generation of hydrogen.
• the invention avoids the problem of gas diffusion from one compartment to another.
• the invention avoids the use of a gas-tight membrane.
• the device according to the invention is thus less limited in terms of operating pressure limit than devices generating the gases simultaneously.
• the device according to the invention comprises only two electrodes.
• the device according to the invention comprises an electrical connection 30, 40 making it possible to manage (i) the load, when the electrical circuit 30 electrically connects the electrodes 10, 20 to the generator 35, and (ii) the discharge of the device 1 when the electrical circuit 40 electrically connects the electrodes 10, 20 to the discharge device 45, the electrical connection 30, 40 “both capable of making the positive electrode 20 function successively as electrode OER 20a and electrode FIER 20b.
• the present invention makes it possible to simplify and optimize the prior systems by implementing only two electrodes, the first electrode playing the role of OER and FIER electrode successively.
• a suitable polarization potential is applied via a voltage generator between the positive electrode OER and the negative redox electrode. Water is oxidized to oxygen at the positive electrode while Mm+ species are reduced to metal M at the second electrode forming the negative electrode.
• the positive (catalytic electrode) and negative (redox electrode in the reduced state) electrodes are disconnected from the generator.
• said electrodes are connected to an electrical discharge circuit (of the discharge resistor type).
• the discharge circuit is conventionally referred to as an electrical discharge circuit. They are then the seat of the spontaneous reaction between the water and the metal, leading to the generation of H 2 at the positive electrode (which becomes a HER electrode) and to the oxidation of the metal M into Mm+ cations at the negative electrode. As the reaction is spontaneous, an electric potential is also produced.
• the generator connection and generator disconnection steps are advantageously successive and cyclical.
• the passage from the circuit connected to the generator to the circuit connected to one or more electronic components, such as for example one or more discharge devices or resistors, or equivalent devices forming for example a receiver dipole, is carried out by a control module or control of electrical circuits.
• This passage can for example be made by means of one or more electrical switches.
• the electrical switches are controlled or driven by one or more control or steering modules positioning the electrical switch(es) according to the electrolysis or conversion steps for electrical operation in contact either with the generator(s) or with the discharge electronic component(s), such as a discharge resistor.
• discharge resistor is meant very broadly a device opposing a resistance to the electric current flowing in the discharge circuit, this term therefore covers capacitors, and more generally any dipole or multi-pole receiver.
• the operation of the system is similar to that of an accumulator (with limited performance).
• the electrolysis reaction under polarization corresponds to a charge while the spontaneous conversion reaction corresponds to the discharge of the system.
• the conversion step is carried out when the negative electrode is in the reduced state, preferably completely reduced, that is to say the available oxidized metallic element M m+ has been reduced to element metal M.
• Said electrode is then connected to the positive electrode via an electric discharge circuit (also called external circuit), the latter then forms an electrode HER.
• the system is then composed of the metallic negative electrode (redox electrode) and a positive HER electrode.
• the conversion step implements a spontaneous oxidation reaction of the metal by the aqueous medium, the HER electrode then generates hydrogen.
• the redox couple is chosen from among the redox couples Pb 2+ /Pb, Zn 2+ /Zn, Sn 2+ /Sn, Mo3+/Mo, Ni 2+ /Ni, Co 2+ /Co.
• both electrodes (negative and positive) are immersed in an aqueous electrolyte.
• the aqueous electrolyte has an acid pH, one then speaks of an acid medium.
• the aqueous electrolyte has a basic pH, one then speaks of a basic medium.
• the aqueous electrolyte comprises the metallic element M m+ .
• M m+ in the electrolyte is in an ionic form, the counterion of which is preferably chosen from the group comprising sulphates, oxides, nitrates, chlorides, citrates, phosphates, carbonates, fluorides, bromides, oxides, aqueous hydroxide solutions of alkali metals or alkaline-earth metals and mixtures thereof.
• the aqueous electrolyte comprises sulfuric acid (H 2 SO 4 ), or potash (KOH).
• the basic electrolyte can also be sodium-based (NaOH).
• the positive electrode forming the OER and/or HER electrode comprises or consists, at least at the surface, of one or more catalysts.
• the most effective catalyst for HER electrodes remains platinum (Pt).
• the platinum is a bifunctional catalyst.
• the bifunctional catalysts for the HER and OER electrodes are for example bimetallic or tri-metallic alloys, in particular based on Nickel, such as NiMo, NiCo, NiFe, NiMoFe, NiMoCo, NiMoN, NiFeN. Mention may also be made of M0C0 or M0O2 type compounds.
• M represents Pb and M m+ represents PbSC> 4 and the electrolyte is acid (H2SO4).
• M represents Zn and M m+ represents Zn 2+ (potentially in Zn(OH) 2 or Zn(OH 4 ] 2 form) and the electrolyte is basic.
• the negative electrode functions as a redox electrode and comprises a substrate and at least one metallic element M in reduced form and/or in oxidized form M m+ , depending on the progress of the charge/discharge cycle .
• the substrate of the redox electrode has an overvoltage vis-à-vis the release of hydrogen, thus preferentially allowing the metal deposit to the formation of hh.
• the substrate of the redox electrode is of the same nature as the deposited metal.
• the substrate can be chosen from lead, zinc, tin, molybdenum, nickel, cobalt.
• the substrate of the redox electrode is a stable metal with respect to the aqueous medium (aqueous electrolyte).
• the substrate of the redox electrode is made of lead, copper, or cobalt.
• the substrate of the redox electrode is made of zinc or nickel.
• the species M m+ is preferentially present within the electrode so as to promote the efficiency of the conversion process.
• the redox electrode comprises on the surface and as a substrate the metallic element.
• a PbSC redox electrode (insoluble in an H 2 SO 4 medium) which is reduced to lead Pb is used on a substrate consisting of or comprising lead.
• This aspect is independently patentable, and the invention also covers a device and method implementing a PbSC redox electrode (insoluble in an H 2 SO 4 medium) which is reduced to lead Pb on a substrate consisting of or comprising lead.
• the invention relates to: a process for generating hydrogen by electrolysis of water, characterized in that it implements a device comprising a hydrogen evolution reaction electrode (HER), an oxygen evolution reaction electrode (OER), said electrodes being able to form a single and same electrode, and a redox electrode comprising the PbSC/Pb redox couple on a substrate consisting of or comprising lead, said electrodes immersing in an electrolyte aqueous, said method comprising at least: a step of electrolysis by power supply inducing a reduction of the metallic element in oxidized form M m+ into a reduced metallic element M in solid form, the metal exhibiting an H 2 overvoltage, and inducing the generation of oxygen O 2 by the OER electrode; a step of conversion by spontaneous reaction at the HER electrode and generating hydrogen H 2 and the oxidation of the metallic element in reduced form M into metallic element in oxidized form M m+ at the redox electrode.
• the invention also relates to a device for
• At least one closed enclosure intended to contain at least one aqueous electrolyte
• Electrodes being able to form a single and same electrode, intended to be immersed in the electrolyte;
• At least one electrode forming a redox electrode comprising the redox couple PbSO Pb on a substrate consisting of or comprising lead and intended to be immersed in the electrolyte;
• the species M m+ is in solution.
• the species M m+ in solution is present at a sufficient concentration not to be limited by the diffusional supply of matter. A supply of material by convection is then preferable.
• the electrolysis and conversion steps are linked so as to produce cycles of successive “charges/discharges”.
• a cell inerting phase is carried out systematically between the electrolysis and conversion steps. This involves saturating the electrolyte with inert gas (typically N2) to drive out the residual gas present in the electrolyte.
• inert gas typically N2
• the residual oxygen present in the aqueous electrolyte is expelled by saturation of the medium with the inert gas.
• the residual hydrogen present in the aqueous electrolyte is expelled by saturation of the medium with inert gas.
• the process of the invention allows the production of hydrogen gas under pressure by electrochemical means, in a decoupled manner, to reach high pressures in hydrogen gas, for example >50 bars.
• the gaseous hydrogen produced is collected, preferably under a pressure greater than atmospheric pressure, and typically at least 10 bars.
• the hydrogen gas thus collected is optionally stored outside the enclosure in an H 2 storage tank.
• the device according to the invention comprises a device for storing gaseous hydrogen generated by the process, a device for storing gaseous oxygen generated by the process and advantageously an energy storage device electricity generated by the process.
• the direct current power supply delivers a current density i (A/m 2 ) of between 100 and 5000, preferably 200 and 3000, and even more preferably 400 and 2000 A/m 2 .
• Figure 1 is a schematic representation of the device for implementing the method according to the invention, implemented during an electrolysis step.
• FIG 2 is a schematic representation of the device for implementing the method according to the invention, implemented during a conversion step.
• Example 1 Device according to the invention operating in acid electrolyte
• Acid electrolysers perform best in terms of operating current density and response dynamics.
• the device and method according to the invention associates, within an electrochemical cell 1, a redox electrode 10 of Pb(substrate)/PbSO4 with a positive electrode 20 of platinum, in the presence of sulfuric acid as as electrolyte 50.
• the single positive electrode 20 is designated 20a when it forms an OER electrode and 20b when it forms an HER electrode.
• the Pb/PbSC redox electrode 10 is the negative electrode conventionally used in the operation of lead batteries in the presence of a 25% H 2 SO 4 electrolyte, whose redox behavior is governed by the equation:
• the Redox potential of this electrode is -0.358V vs ENH (hydrogen reference electrode).
• the first electrolysis stage generation of oxygen; figure 1
• a second stage consisting of a spontaneous reaction generating hydrogen and electrical energy (figure 2).
• a PbSÜ4 electrode resulting from an initial stage of oxidation of a lead electrode resulting from the technology of lead accumulators is preferably used.
• the electrodes 10, 20a are connected to a generator 35 by a first electrical circuit 30.
• the negative electrode 10 of PbSC> 4 (on Pb substrate) is reduced to Pb while the positive electrode 20a oxidizes the water to oxygen, according to the following reactions:
• the first electrolysis step is an oxygen generation step, as shown in figure 1.
• the high overvoltage of H2 release on Lead means that it remains stable in a protonated medium.
• Electrode 20a acts as HER electrode 20b.
• the second step is the hydrogen generation step, as shown in Figure 2.
• Example 2 Device according to the invention operating in alkaline electrolyte (basic)
• Zinc-Air accumulators typically operate in a basic medium (KOH 1 M to 6 M).
• the deposition of zinc is more effective in a basic medium with respect to the release of hydrogen, and the stability of zinc is also much better than in an acid medium.
• the decoupled electrolysis system 1 implements a catalytic electrode 20 based on a bifunctional NiMoCo trimetallic alloy, associated with a metal electrode 10 forming the redox electrode and seat of a zinc deposit during the charging and oxidation of this zinc during discharge.
• the electrolyte 50 is basic and contains a zinc salt, which is in the form of Zn(OH) 4 2_ at the pH under consideration.
• a sufficient polarization (voltage 3 1.6V) is applied between the positive electrode 20 (OER electrode 20a) and the negative electrode 10 (metal cathode, ie the redox electrode) stable in an alkaline medium.
• the hydroxyl anions of the water are oxidized to oxygen on the positive electrode OER 20a and the zinc salt is reduced at the negative electrode 10 where a zinc deposit is formed, according to the following equations:
• the electrodes are disconnected from the electric circuit 30 comprising a generator 35 and connected to one another via an electric discharge circuit 40 comprising a device forming a resistor 45 (discharge resistor).
• the reaction between zinc and water is then spontaneous.
• the zinc is oxidized and dissolves in the electrolyte 50 while hydrogen is formed at the positive electrode HER 20b, according to the following equations:

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