WO2023046775A1

WO2023046775A1 - Method for continuously generating hydrogen by electrolysis of water via a decoupled approach

Info

Publication number: WO2023046775A1
Application number: PCT/EP2022/076266
Authority: WO
Inventors: David AYMÉ-PERROT DAVID
Original assignee: Totalenergies Onetech
Priority date: 2021-09-21
Filing date: 2022-09-21
Publication date: 2023-03-30
Also published as: FR3127234A1

Abstract

The present application relates to a method for continuously generating hydrogen by electrolysis of water, which comprises: - polarising an electrochemical cell, the voltage U being greater than or equal to 1.5 V, said electrochemical cell comprising a negative electrode compartment and a positive electrode compartment; - producing hydrogen from the reduction of an aqueous electrolyte in said negative electrode compartment; - oxidising a reducing agent "Red" to an oxidant "Ox", in said positive electrode compartment, said reducing agent being present in an aqueous anolyte fed by fluid circulation into the positive compartment; - fluidically circulating the anolyte containing the oxidant "Ox" from said positive electrode compartment to a device comprising a catalytic species promoting OER; - reducing the oxidant "Ox" to its reduced form "Red" and producing oxygen in the device comprising the OEC catalytic species.

Description

Process for the continuous generation of hydrogen by electrolysis of water via a decoupled approach

The present invention relates to a process for the continuous generation of hydrogen by electrolysis of water. In particular, the invention proposes such a process with decoupled stages, i.e. production of hydrogen and oxygen staggered in time and/or in space.

State of the art

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 respectively referred to as the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER).

There are 3 types of water electrolyser technologies: 2 which are mature in liquid electrolyte, namely in acid or alkaline medium, and another in the gas phase at high temperature (SOEC, "Solid Oxide Electrolyzer Cell" in English ) which still needs to be optimized. Acidic systems are called proton exchange membrane (PEM) electrolysers. They are in particular equipped with a membrane based on proton-conducting perfluorosulfonic acid (for example Nation®, which is a perfluorinated copolymer comprising perfluorinated side chains whose free ends each carry a sulfonic acid) which ensures both the ionic conductivity of the cell and gas tightness between the 2 anode and cathode compartments. This membrane remains a key but expensive element of “PEM” cells. In an alkaline medium, porous composite membranes, called diaphragms (polysulfone type, polyphenylene sulphide, reinforced with a metal oxide) act as a separating membrane. They allow the circulation of hydroxide ions from the electrolyte, which ensures the ionic conductivity of the cell but are much less gastight than PEMs. It should be noted that the high temperature technology is based on a ceramic which conducts O ^2- ions at high temperature (>500°C) used as separating membrane/electrolyte. PEM-type electrolysers 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. However, the stability of the materials is obviously severely tested in acidic environments, which requires the use of expensive materials for the key elements of the cell: the bipolar plates and other porous transport layers are typically titanium-based covered with platinum and gold. The catalysts used are typically platinum (Pt) at the cathode (HER) and iridium oxide (lrC>2) at the anode (OER). Catalysts in an alkaline medium are generally Nickel alloys which remain less expensive and have good stability.

In general, the simultaneous generation of gases (oxygen and hydrogen) within the electrolyser has certain limits. One thinks in particular of the speed of the hydrogen evolution reaction (HER) which is necessarily dependent on the very slow kinetics of the oxygen evolution reaction (OER), which requires imposing a significant overvoltage on the cell electrochemical, and therefore reduces the energy efficiency of electrolysis.

PEM systems, thanks to the chemical and mechanical robustness of the membranes, can operate with significant pressure differences between the electrochemical compartments, which is not possible with alkaline systems which require the same pressure between the cathodic compartments and anodic.

The diffusion of gases through the membrane (“gas crossover” in English) remains problematic for optimal efficiency.

This phenomenon of gas diffusion will be all the more important during slow operating regimes. Such gas mixtures involve monitoring of the quantities involved and post-purification of the hydrogen.

In the event of an incident on the membrane, the then very significant reactivity between O2 and H ₂ represents a real danger.

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. In other words, hydrogen and oxygen are not produced simultaneously and/or at the same place 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.

Different decoupled water electrolysis systems are listed in the literature. The use of Redox mediators was 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. First, the redox mediator (for example phosphomolybdic acid (H3M012O40P) will be reduced at the cathode under polarization with release of oxygen at the anode. Then in a second time, the reduced mediator will be reoxidized at the anode and the hydrogen produced at the cathode.The same approach is found with a polyaniline electrode used as an intermediate redox couple.

Other approaches bring together a specific faradic electrode in contact with a hydrogen-generating electrode.

In US2020/040467, Rothschild et al. claim an oxygen generation system bringing together two electrodes, one of which, one of the electrodes, consisting of a chemical species in the oxidized state, is capable of being reduced in the absence of electrical polarization to generate 'oxygen. Typically, a positive Ni(OH) ₂ electrode which has good reversibility is coupled to a negative water reduction electrode (HER) within an alkaline cell. Thus, when charging the system, hydrogen is generated at the cathode while nickel hydroxide is oxidized to nickel oxyhydroxide (NiOOH) with good energy efficiency (due to the reversibility of the NiOOH/Ni redox couple (OH) ₂ ). Once this electrode is fully charged, the power supply to the system is stopped, the system no longer generates hydrogen and the positive electrode will regenerate. The authors have developed a thermal regeneration of the NiOOH electrode: by heating the cell to 95°C, the NiOOH electrode is reduced by water to Ni(OH) ₂ with release of oxygen. The system can then be charged again and produce hydrogen. It should be noted that to be fully relevant in terms of gain in energy efficiency, 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, this which remains limiting.

Another approach described in WO2019/193283 consists in implementing an electrochemical process for producing gaseous hydrogen by electrolysis of a preferentially aqueous electrolyte, then electrochemical conversion of H+ ions into gaseous hydrogen within a device with 3 electrodes . The first stage of electrolysis by polarization consists in producing oxygen at the positive electrode and in reducing an ionic chemical species present within the electrolyte in metallic form at the negative electrode. During the second step, by coupling a HER electrode with the metal electrode, the metal deposited on the latter reoxidizes and hydrogen is formed spontaneously on the HER electrode. Unlike the previous approach, hydrogen is here generated during the second step of the process. In the case of a loss of efficiency with regard to the metal deposit (disintegration during the cycles), this will impact the quantity of hydrogen generated.

The present inventors have identified that a limit of the various approaches mentioned above which consist in the absolute of coupling a faradic electrode (site of a redox reaction) with a HER and/or OER electrode, lies in the use of a faradic electrode whose capacitance is necessarily limited. This reduced capacity therefore imposes multiple cycles (charge/regeneration or electrolysis/conversion) over time. We are talking about operation in discontinuous mode, unlike a conventional electrolyser which operates in continuous mode.

An idea of the present inventors to increase the operating times consists in using, instead of a conventional Faradic electrode, a Faradic electrode supplied with a flow of electrolyte containing a chemical species capable of being reduced or oxidized in the vicinity of said electrode. This principle being that of so-called redox flow batteries where the appropriate chemical species (oxidant and reducing agent) are stored in separate reservoirs supplying the anode and cathode compartments of the electrochemical cell in a fluidic manner. The energy of the battery (or the capacity of the system) then depends directly on the size of the tanks. The other advantage of such an approach consists in producing the gases in a delocalized way with respect to the electrochemical flow cell. In particular, flow batteries of the V ³⁺ /V ²⁺ type at the negative electrode and Ce ³⁺ /Ce ⁴⁺ at the positive electrode are known. These two couples have potentials beyond the thermodynamic window of water (1.23V). It has been observed (WO2013131838) that given the sufficiently slow kinetics of H ₂ and O ₂ release on the substrate electrodes used, the reactions of reduction of V ³ + _to v ²⁺ at the cathode and oxidation of Ce ³⁺ in Ce ⁴⁺ at the anode are favored. Since the system is under flux, V ²⁺ and Ce ⁴⁺ are therefore transported to separate reservoirs outside the electrochemical cell. The two ionic species can then be sent to catalytic columns (reservoirs) containing catalysts suitable for HER and OER reactions respectively, V ²⁺ is then oxidized by protons, which generates hydrogen, and Ce ⁴⁺ is reduced by water, which generates oxygen. The electrolytic species are regenerated during the generation of gases. This device is not actually a battery, it is an electrochemical device which is charged under polarization and then discharges by spontaneous reactions in contact with catalysts. Aims of the invention

The aim of the invention is to solve the technical problem of providing a device and a process for the decoupled electrolysis of water.

The object of the invention is in particular to solve the technical problem of providing a device and a 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.

Furthermore, the present invention particularly aims to solve the technical problem of simplifying and optimizing prior systems.

Principle of the invention

The invention consists in producing pressurized hydrogen via a decoupled electrolysis process: the production of hydrogen and oxygen does not take place simultaneously within the same cell, in order to promote the safety of the system and good conversion efficiency.

The invention relates to a process for the continuous generation of hydrogen by electrolysis of water, characterized in that said process comprises:

- the polarization of an electrochemical cell, the voltage U being greater than or equal to 1.5 V, said electrochemical cell comprising a negative electrode compartment and a positive electrode compartment;

- the production of hydrogen (H2) from the reduction of an aqueous electrolyte in said negative electrode compartment;

- the oxidation of a “Red” reducer into an “Ox” oxidant (redox couple Ox/Red), in the said positive electrode compartment, the said reducer being present in an aqueous anolyte supplied by fluid circulation within the positive compartment ;

- the fluidic circulation of the anolyte containing the oxidant "Ox" of the said positive electrode compartment towards a device comprising a catalytic species promoting the OER (OEC);

- the reduction of the oxidant “Ox” to its reduced form “Red” (regeneration of the anolyte) and the production of oxygen (O2) in the device comprising the catalytic species OEC.

The invention also relates to a method as described above, characterized in that it implements the reaction in the negative electrode compartment:

_OIJ 2 H ₂ O ₊ 2c- - H ₂ + 2 OH , _{in an alkaline medium} . _And in the positive electrode compartment, the oxidation reaction:

in which "Red" represents the reducer and "Ox" represents the oxidant of a redox couple Ox/Red, the reaction not indicating the number of moles of "Red" and "Ox" involved, n representing the number of moles electrons exchanged.

The invention also relates to a method, as described above, characterized in that the "Red" reducing agent is transferred by fluid circulation from the device comprising the OEC catalytic species to a storage or buffer tank, optionally by circulation through the positive electrode compartment.

The invention also relates to a method, as described above, characterized in that the device comprising the OEC catalytic species forms a second electrochemical cell comprising a first positive electrode compartment and a second negative electrode compartment, the said negative electrode comprising said OEC catalytic species, said process comprising reducing the oxidant "Ox" to a reduced form "Red" in the positive electrode compartment and producing oxygen (O2) from the water (H2O) or hydroxyl ions in the negative electrode compartment, said positive electrode compartment and said negative electrode compartment being separated by a membrane conducting protons or hydroxyl ions.

The invention also relates to a method, as described above, characterized in that it comprises the production of a positive voltage by the device comprising the catalytic species.

The invention also relates to a method, as described above, characterized in that it involves a redox couple Ox/Red having a standard redox potential higher than that of the couple O2/H2O (E°O2/H ₂ O=1.23V), and for example chosen from among the redox couples MnO4′/Mn ²⁺ , Mn ³⁺ /Mn ²⁺ , Ce ⁴⁺ /Ce ³⁺ , Co ³⁺ /Co ²⁺ , BrO ³ 7Br.

The invention also relates to a method, as described above, characterized in that it comprises a continuous supply of the anolyte containing the "Red" reducer into the positive electrode compartment.

The invention also relates to a device (1) for implementing a method according to any one of the preceding claims, characterized in that it comprises:

- at least one fluid supply system (reservoir (50, 250, 350) and/or circulation system) intended to contain or containing at least one aqueous electrolyte forming an anolyte (55, 255, 355) containing at least one reducer " Red” of a redox couple Ox/Red; - at least one electrochemical cell (20, 220, 320, 420, 520) comprising, in a positive electrode compartment (24, 224, 324, 424, 524) an electrode (22, 222, 322, 422, 522) intended to be dipped or immersed in the electrolyte (55, 255, 355, 455, 555) supplied by the fluidic supply system, said electrode being capable of oxidizing or oxidizing the reducer "Red" into an oxidized form "Ox" and comprising, in a negative electrode compartment (23, 223, 323, 423, 523), an electrode (21, 221, 321, 421, 521) capable of forming or forming an HER electrode generating hydrogen by reduction of proton (H ⁺ ) or water (H ₂ O);

- said negative electrode compartment (23, 223, 323, 423, 523) and said positive electrode compartment (24, 224, 324, 424, 524) being separated by a membrane (30, 230, 330, 430, 530) conducts protons or hydroxyl ions;

- at least one device (60, 260, 360, 460, 560) comprising a catalytic species capable of promoting the oxidation reaction of water to oxygen (O ₂ ) by the oxidant "Ox", which is reduced under “Red” shape;

- at least one device (80, 280, 380, 480, 580) for circulating the aqueous solution from the positive electrode compartment to the compartment comprising the OEC catalytic species.

The present invention also relates to a device (1) as described above, characterized in that the device (60, 260, 360, 460, 560) comprises the catalytic species OEC in the form of a catalytic bed or a grid catalytic particles

The present invention also relates to a device (1) as described above, characterized in that the device (560) comprising the OEC catalytic species forms a second electrochemical cell comprising a first compartment (561) capable of reducing or reducing the 'Ox' oxidant to a reduced 'Red' form and a second compartment (562) capable of oxidizing or oxidizing water (H ₂ O) or hydroxyl ions to oxygen (O ₂ ), said first compartment and said second compartment being separated by a proton or hydroxyl ion exchange membrane (530).

The present invention also relates to a device (1) as described above, characterized in that the device (560) comprises the catalytic species OEC within the electrode of the compartment (562).

The invention also relates to a device 1 for implementing the method according to the invention, characterized in that it comprises: - at least one fluid supply system (reservoir 50 and/or circulation system) intended to contain or containing at least one aqueous electrolyte forming an anolyte 55 containing at least one “Red” reducer of a redox couple Ox/Red;

- at least one electrochemical cell 20 comprising, in a positive electrode compartment 24, an electrode 22 intended to be immersed or immersed in the electrolyte 55 provided by the fluid supply system, said electrode being capable of oxidizing or oxidizing the reducer "Red" into an oxidized form "Ox" and comprising, in a negative electrode compartment 23, an electrode 21 capable of forming or forming an HER electrode generating hydrogen by reduction of proton (H ⁺ ) or water ( H2O);

- said negative electrode compartment 23 and said positive electrode compartment (24) being separated by a membrane 30 which conducts protons or hydroxyl ions;

- at least one compartment 60 comprising a catalytic species capable of promoting the oxidation reaction of water to oxygen (O2) by the oxidant “Ox”, which is reduced in the “Red” form;

- at least one device 80 for circulating the aqueous solution from the positive electrode compartment to the compartment comprising the OEC catalytic species.

Typically, a power supply 70, 270, 370, 470, 570 electrically connects the positive 22, 222, 322, 422, 522 and negative 21, 221, 321, 421, 521 electrodes.

The negative electrode is based on a catalyst promoting the release of hydrogen, for example platinum (Pt) in an acid medium. We speak of “HEC” (“Hydrogen Evolution Catalyst) for this type of catalyst.

According to one embodiment, the device 1, 201, 301, 401, 501 comprises at least one gaseous oxygen evacuation pipe generated by the process, and independently, at least one gaseous hydrogen evacuation pipe. generated by the process.

Advantageously, one or more reservoirs containing the aqueous anolyte, which contains the "Red" reducer of the redox couple Ox/Red, is fluidically connected to the positive compartment of the electrochemical cell via a fluid circulation system, typically comprising one or more circulation, for example pipes, and one or more pumping systems to supply it.

Advantageously, the redox pair Ox/Red associated with the reducer “Red” has a standard redox potential higher than that of the pair O2/H2O (E°O2/H ₂ O=1.23V). The oxidation reaction of water (release of oxygen) "OER" is known to be kinetically very slow. The electrode within the positive compartment is based on an electrically conductive substrate that does not promote said OER reaction, for example a steel stainless steel or a graphite electrode, thus allowing under electrical polarization the prior oxidation of the reducing agent present within the anolyte. Among the possible redox couples, the following may be cited: MnC/Mn ² *, Mn ³⁺ /Mn ²⁺ , Ce ⁴⁺ /Ce ³⁺ , Co ³⁺ /Co ²⁺ , BrOs /Br.

(*) Highly dependent on acid medium and acid concentration

Advantageously, the “Red” reducer (of the redox pair Ox/Red) is soluble in aqueous solution to ensure fluid circulation without difficulty.

Under polarization, the system generates hydrogen by reduction of the aqueous electrolyte (reduction of the proton in an acid medium or of water in an alkaline medium,) at the negative electrode HER while the "Red" reducer is oxidized to the positive electrode in the form of an oxidant “Ox”.

The resulting anolyte comprising the oxidant "Ox" is evacuated by a circulation system (for example pipes comprising one or more pumps, etc.) to a second storage tank (2).

This tank has the particularity of containing a catalytic species forming a catalyst promoting the OER reaction, we speak of OEC (oxygen evolution catalyst).

According to a variant, the OEC catalytic species comprises or consists of lrO ₂ and/or RuO ₂ .

Typically, as the anolyte (aqueous solution containing the oxidant “Ox”) is brought into contact within the reservoir 60, 260, 360 with the OEC catalytic species, a spontaneous redox reaction takes place between the oxidant “Ox” and water (or hydroxyl ions at high pH), generating oxygen and reducing the chemical species “Ox” which reverts to the reducing state “Red”. The OER reaction is favored by the catalytic species. Nevertheless, even in the presence of a catalyst, a significant overvoltage is necessary for the reaction to take place at a suitable rate. Thus advantageously, the redox pair "Ox/Red" must have a standard redox potential greater than a potential equivalent to the standard oxidation potential of water to which is added an overvoltage of at least 250 mV (E=1, 23V+ 0.25=1.48V) so that the spontaneous reaction oxidation-reduction takes place (Ox + H ₂ O -> Red + O ₂ ). This step makes it possible to regenerate the anolyte via the generation of oxygen.

Therefore, advantageously, the hydrogen is generated within the electrochemical cell while the oxygen is generated outside of it in an ancillary device, which avoids the potential mixing of these two gases.

According to one embodiment, the supply of anolyte is continuous. Advantageously, the continuous supply of the anolyte within the electrochemical cell makes it possible to operate over a longer time than with a simple faradic electrode immersed within the positive compartment which requires a multitude of cycles (of the charge/discharge type ). As it is, the operating time remains dependent on the size of the anolyte reservoir and/or the chosen system architecture.

In the figures:

Figures 1 to 5 represent a schematic view of different variants of a device and implementation of the method according to the present invention.

In FIG. 1, device 1 constitutes the elementary brick of the system. Indeed the device 1, and process for the continuous generation of hydrogen by electrolysis of water, comprises a tank 50 intended to contain or containing at least one aqueous electrolyte forming an anolyte 55 containing a reducing agent “Red”; at least one electrochemical cell 20 comprising, in a positive electrode compartment 24, an electrode 22 intended to be immersed or immersed in the electrolyte (anolyte) 55, said electrode being capable of oxidizing or oxidizing the reducing agent “Red” into a form oxidized “Ox” and comprising, in a negative electrode compartment 23, an electrode 21 capable of forming or forming an HER electrode generating hydrogen by reduction of the aqueous electrolyte (the 2 reactions taking place under electric polarization); said negative electrode compartment 23 and said positive electrode compartment 24 being separated by a membrane 30 (proton or hydroxyl ion exchanger or a composite diaphragm); at least one compartment 60 comprising an OEC catalytic species capable of promoting the spontaneous oxidation of water into oxygen by the oxidant “Ox”, which is then reduced (in its reduced form “Red”); at least one device 80 for circulating the aqueous solution from the positive electrode compartment to the compartment 60 comprising the catalytic species OEC. The anolyte 55 circulates in a circulation device 80 making it possible to circulate the anolyte 55 through the electrochemical cell 20. More precisely, the anolyte 55 circulates from the reservoir 50 towards the electrochemical cell 20 in a circulation device 81 typically comprising one or more fluid circulation lines and one or more circulation pumps. The anolyte 55 circulates from the electrochemical cell 20 to the device 60 comprising the OEC catalytic species in a circulation device 80, 82 typically comprising one or more fluidic circulation lines and one or more circulation pumps.

In this configuration, the electrolysis process is interrupted once all the anolyte from reservoir 50 has been consumed. The reinjection of the regenerated anolyte into the tank 60 is then required so that the electrolysis can take place over longer periods.

The anolyte can be reinjected as far as the weir 50 via the positive compartment 24 of the electrochemical cell 20 in the absence of electrical polarization at the terminals thereof. The anolyte is then transferred from reservoir 60 to electrochemical cell 20 via circulation system 80; then from the electrochemical cell 20 to the tank 50 via the circulation device 81. This reinjection step requires time during which the electrolysis of the water cannot take place.

The two approaches are possible to optimize the reinjection of the anolyte within the system and to limit the dead times of operation, namely the device 201 (figure 2) and the device 301 (figures).

According to a variant, the device and the method according to the present invention allow operation of the system according to FIG. 1 and in reverse mode. According to this variant, illustrated in FIG. 2, the tank 250 is also equipped with a device comprising the catalytic species OEC. According to this variant, the device 201 and process for the continuous generation of hydrogen by electrolysis of water comprises a tank 250 intended to contain or containing at least one aqueous electrolyte forming an anolyte 255 initially containing a “Red” reducing agent; at least one electrochemical cell 220 comprising, in a positive electrode compartment 224, an electrode 222 intended to be dipped or immersed in the electrolyte 255, said electrode being capable of oxidizing or oxidizing the reducer “Red” into an oxidized form “Ox and comprising, in a negative electrode compartment 223, an electrode 221 capable of forming or forming an HER electrode generating hydrogen by reduction of proton (H ⁺ ), or water (H2O) (the 2 reactions taking place under bias); said negative electrode compartment 223 and said positive electrode compartment 224 being separated by a membrane 230 (proton or hydroxyl ion exchanger or composite diaphragm); at least one compartment 260 comprising an OEC catalytic species capable of promoting the spontaneous oxidation of water into oxygen by the oxidant “Ox”, which is then reduced (in its reduced form “Red”); at least one device 280 for circulating the aqueous solution from the positive electrode compartment to the compartment 260 comprising the catalytic species OEC.

Once the oxidant is completely reduced (in “Red” form). The system can operate in reverse mode (flow in the other direction).

More specifically, the anolyte 255 then circulates from the device 260 to the electrochemical cell 220 in a circulation device 282 typically comprising one or more fluidic circulation lines and one or more circulation pumps.

The electrochemical cell 220 being maintained under electrical polarization, the "Red" reducer is oxidized in the "Ox" form in the positive compartment while hydrogen is produced in the negative compartment.

The anolyte 255 containing the oxidant "Ox" circulates from the electrochemical cell 220 to the reservoir 250 through a circulation device 281 typically comprising one or more fluidic circulation pipes and one or more circulation pumps. Compartment 250 comprises an OEC catalytic species capable of promoting the spontaneous oxidation of water into oxygen (O2) by means of the oxidant “Ox”, which is then reduced to its reduced form “Red”. Once the “Ox” oxidant is completely reduced (in “Red” form), the system can be restarted in the other direction.

However, this solution has two drawbacks:

The system operates discontinuously (downtime for the change of direction of the flow); And

The architecture requires doubling the amount of catalyst (OEC) to be used.

It then seems more judicious from a technical-economic point of view, to consider a fluidic connection between the reservoir 50 and the device 60 by a circulation system, as illustrated in Figure 3, where the reservoir 350 and the device 360 are connected by a circulation system or device 380. Typically, tank 350 acts as a buffer storage tank. According to another variant, the device, and method, according to the invention comprises only the device 460, as illustrated in Figure 4.

Such a system architecture makes it possible to envisage continuous operation.

Thus, in FIG. 3, the device 301 and process for the continuous generation of hydrogen by electrolysis of water comprises a reservoir 350 intended to contain or containing at least one aqueous electrolyte forming an anolyte 355, containing a reducing agent. In FIG. 4, the device 401 and process for the continuous generation of hydrogen by electrolysis of water does not, strictly speaking, comprise a reservoir intended to contain or containing at least one aqueous electrolyte forming anolyte 455, containing a reducing agent, which is contained in the circulation device 480. In Figures 3 and 4, the device 301, 401 and method according to the invention further comprises at least one electrochemical cell 320, 420, comprising, in a positive electrode compartment 324, 424 an electrode 322, 422 intended to be immersed or immersed in the electrolyte 355, 455, said electrode being capable of oxidizing or oxidizing the reducer "Red" into an oxidized form "Ox" and comprising, in a negative electrode compartment 323, 423 an electrode 321, 421 capable to form or forming a HER electrode generating hydrogen by reduction of proton (H ⁺ ) or water (H2O); said negative electrode compartment 323, 423 and said positive electrode compartment 324, 424 being separated by a membrane 330, 430 (proton or hydroxyl ion exchanger or composite diaphragm); at least one compartment 360, 460 comprising a catalytic species capable of promoting the spontaneous oxidation of water into oxygen (O2) by the oxidant “Ox”, which is then reduced to its reduced form “Red”; at least one device 382, 480 for circulation of the aqueous solution from the positive electrode compartment to the compartment comprising the catalytic species OEC. More specifically, in Figure 3, anolyte 355 flows from reservoir 350 to electrochemical cell 320 in a circulation device 381 typically comprising one or more fluid circulation lines and one or more circulation pumps. The anolyte 355 circulates from the electrochemical cell 320 to the device 360 through a circulation device 382 typically comprising one or more fluid circulation pipes and one or more circulation pumps.

In Figure 4, anolyte 455 flows from electrochemical cell 420 to device 460 and then returns to electrochemical cell 420 through a circulation device 480 typically comprising one or more fluid circulation lines and one or more circulation pumps. Finally, advantageously, according to an embodiment represented in FIG. 5, the device 560 comprising an OEC catalytic species forms an electrochemical cell. According to this embodiment, the reaction in the device 560 which is spontaneous between the oxidant and the water, takes place within an electrochemical cell 560 with two electrodes brought into contact via an external electrical discharge circuit 540. oxidation of water to oxygen takes place at the negative electrode containing the catalytic species, while reduction of the oxidant takes place at the positive electrode of cell 560, thus generating an electrical voltage across the terminals of the cell 560 (U < E°Ox/Red — E°O ₂ /H ₂ O-QOE).

The device 60, 260, 360, 460 of FIGS. 1 to 4 comprising the catalytic species OEC can therefore be replaced by a (second) electrochemical cell 560. For example, the cell 560 can comprise a negative electrode based on a catalyst for the OER (e.g. lrÛ2, RUO2) and a positive electrode made from a conductive material electrical (preferably stable in the medium and the potential conditions), for example a stainless steel electrode, or a carbon-based electrode).

Other aims, characteristics and advantages of the invention will appear clearly to those skilled in the art on reading the explanatory description which refers to examples which are given solely by way of illustration and which do not in any way way limit the scope of the invention.

The examples form an integral part of the present invention and any feature appearing new with respect to any state of the prior art from the description taken as a whole, including the examples, forms an integral part of the invention in its function and in its generality.

Thus, each example is general in scope.

On the other hand, in the examples, all the percentages are given by weight, unless otherwise indicated, and the temperature is expressed in degrees Celsius unless otherwise indicated, and the pressure is atmospheric pressure, unless otherwise indicated.

EXAMPLE 1:

Consider an electrochemical cell composed of a proton-conducting membrane containing perflurosulphonic acid (Nation® type), a negative electrode containing a platinum-based catalyst in contact with the membrane, and a porous graphite positive electrode. The positive compartment is connected to a first reservoir containing a 1 M solution of cerium nitrate Ce(NOs)3 in 1 M HNO3.

A voltage U > 1.75 V is applied to the system: hydrogen is generated in the negative compartment while Ce ³⁺ is oxidized to Ce ⁴⁺ in the positive compartment, according to the following half-reactions:

2H ⁺ + 2 e- Ha

2 Ce ³⁺ 2 Ce ⁴⁺ + 2e-

The Ce ⁴⁺ formed passes through a pipe to a second reservoir which contains a catalytic bed containing particles of iridium oxide (lrC>2).

The acid solution of Ce ⁴⁺ forms oxygen spontaneously in contact with the particles of IrC>2 in order to be regenerated, according to the following reaction:

4 Ce ⁴⁺ + 2H2O 4 Ce ³⁺ + Oa + 4H ⁺

The regenerated Ce ³⁺ acid solution can then be reinjected into the positive compartment of the first electrochemical cell with an adequate supply of pure water to compensate for its consumption during 2 gas generation steps. EXAMPLE 2:

Consider an electrochemical cell composed of a proton-conducting membrane containing perflurosulphonic acid (Nation® type), a negative electrode containing a platinum-based catalyst in contact with the membrane, and a positive electrode in the form of a 316L stainless steel grid. The positive compartment is connected to a first reservoir containing a 1 M solution of Cerium Nitrate Ce(NOs)3 in 1 M HNO3.

2H ⁺ + 2 e - H ₂

2 Ce ⁵⁺ 2 Ce ⁴⁺ + 2e-

The Ce ⁴⁺ passes through a pipe to a second electrochemical cell, more precisely within a compartment containing a porous graphite electrode. Said electrode is in contact via an external discharge circuit with the electrode of the second compartment which is an electrode based on IrC catalytic particles. A Nation® type proton separator membrane separates the 2 compartments.

From then on, a spontaneous oxidation-reduction reaction takes place between the acid solution of Ce ⁴⁺ and the water. The Ce ⁴⁺ is reduced to Ce ³⁺ on the graphite electrode while oxygen is formed in contact with the IrC>2 particles (OER electrode), according to the following half-reactions:

4 Ce ⁱ⁺ + 4e- -> 4 Ce ³ *

2H2O O2 + 4H* + 4e-

The second electrochemical cell supplies a voltage U<E°Ce ⁴⁺ /Ce ³⁺ -E°O2/H2O -nO ₂ /H ₂ O=1.61-1.23-0.25=0.13V.

The regenerated Ce ³⁺ acid solution can then be reinjected into the positive compartment of the first electrochemical cell with an adequate supply of pure water to compensate for its consumption during the 2 gas generation stages (production of hydrogen (H2) and oxygen production (O2)).

Claims

1. Process for the continuous generation of hydrogen by electrolysis of water, characterized in that said process comprises:

- the polarization of an electrochemical cell, the voltage II being greater than or equal to 1.5 V, said electrochemical cell comprising a negative electrode compartment and a positive electrode compartment;

2. Method according to claim 1, characterized in that it implements the reaction in the negative electrode compartment:

in the positive electrode compartment, the oxidation reaction:

Rfid Qx ⁺ n e-, in which “Red” represents the reducer and “Ox” represents the oxidant of a redox couple Ox/Red, the reaction not indicating the number of moles of “Red” and “Ox” involved, n representing the number of moles of electrons exchanged.

3. Method according to claim 1 or 2, characterized in that the "Red" reducer is transferred by fluid circulation from the device comprising the OEC catalytic species to a storage or buffer tank, optionally by circulation through the positive compartment of 'electrode.

4. Method, according to any one of the preceding claims, characterized in that the device comprising the OEC catalytic species forms a second electrochemical cell comprising a first positive electrode compartment and a second negative electrode compartment, the said electrode negative comprising said OEC catalytic species, said process comprising reducing the oxidant "Ox" to a reduced form "Red" in the positive electrode compartment and producing oxygen (O2) from water ( H ₂ O) or hydroxyl ions in the negative electrode compartment, said positive electrode compartment and said negative electrode compartment being separated by a membrane that conducts protons or hydroxyl ions.

5. Method, according to any one of the preceding claims, characterized in that it comprises the production of a positive voltage by the device comprising the catalytic species.

6. Process, according to any one of the preceding claims, characterized in that it involves a redox couple Ox/Red having a standard redox potential higher than that of the couple O2/H2O (E°O2/H ₂ O= 1.23V), and for example chosen from the redox couples MnC − /Mn ²⁺ , Mn ³⁺ /Mn ²⁺ , Ce ⁴⁺ /Ce ³⁺ , Co ³⁺ /Co ²⁺ , BrO ³ 7Br.

7. Method, according to any one of the preceding claims, characterized in that it comprises a continuous supply of the anolyte containing the “Red” reducer into the positive electrode compartment.

8. Device (1) for implementing a method according to any one of the preceding claims, characterized in that it comprises:

- at least one fluid supply system (reservoir (50, 250, 350) and/or circulation system) intended to contain or containing at least one aqueous electrolyte forming an anolyte (55, 255, 355, 455, 555) containing at least one “Red” reducer of a redox couple Ox/Red;

- at least one electrochemical cell (20, 220, 320, 420, 520) comprising, in a positive electrode compartment (24, 224, 324, 424, 524) an electrode (22, 222, 322, 422, 522) intended to be dipped or immersed in the electrolyte (55, 255, 355, 455, 555) supplied by the fluidic supply system, said electrode being capable of oxidizing or oxidizing the reducer "Red" into an oxidized form "Ox" and comprising, in a negative electrode compartment (23, 223, 323, 423, 523), an electrode (21, 221, 321, 18

421, 521) capable of forming or forming a HER electrode generating hydrogen by reduction of proton (H ⁺ ) or water (H ₂ O);

- at least one device (60, 260, 360, 460, 560) comprising a catalytic species capable of promoting the oxidation reaction of water to oxygen (O ₂ ) by the oxidant "Ox", which is reduced under “Red” form;

- at least one device (80, 280, 380, 480, 580) for circulating the aqueous solution from the positive electrode compartment to the compartment comprising the OEC catalytic species. Device according to Claim 8, characterized in that the device (60, 260, 360, 460, 560) comprises the catalytic species OEC in the form of a catalytic bed or of a grid of catalytic particles. Device according to Claim 8 or 9, characterized in that the device (560) comprising the OEC catalytic species forms a second electrochemical cell comprising a first compartment (561) capable of reducing or reducing the oxidant "Ox" to a reduced form "Red" and a second compartment ( 562) capable of oxidizing or oxidizing water (H ₂ O) or hydroxyl ions to oxygen (O ₂ ), said first compartment and said second compartment being separated by a proton or hydroxyl ion exchange membrane (530). Device, according to claim 10, characterized in that the device (560) comprises the catalytic species OEC within the electrode of the compartment (562).