EP3775323A1

EP3775323A1 - Electrochemical method for producing pressurised hydrogen gas by electrolysis and subsequent depolarisation

Info

Publication number: EP3775323A1
Application number: EP19720962.0A
Authority: EP
Inventors: Elisa GRINDLER; François Guillet; Vincent BIZOUARD
Original assignee: Ergosup
Current assignee: Ergosup
Priority date: 2018-04-03
Filing date: 2019-04-03
Publication date: 2021-02-17
Also published as: US20210123145A1; WO2019193280A1; JP2021520451A; FR3079529B1; FR3079529A1

Abstract

The invention relates to an electrochemical method for producing hydrogen gas by electrolysis and subsequent electrochemical conversion of H⁺ ions to H₂ ions by depolarisation. Said method is intended to simply and industrially achieve high hydrogen gas pressures, for example >80 bar. To achieve this, the method consists in implementing a step E¹ of electrolysing one electrolyte to produce oxygen gas and a step C° of converting a redox chemical energy to an electrical energy, with H₂ being produced. In said method, - the electrolyte comprises M^m+ ions of a metal M corresponding to the redox couple (M^m+/M) and A^a+ ions of a depolarisation additive A corresponding to the redox couple (A^a+/A); - the electrolysis step E¹ is initiated by supplying power between the anode and the cathode; A^a+and M^m+ are respectively deposited as A and M on the cathode during the electrolysis E¹ and oxygen gas is released at the anode; - the electrolysis E¹ is interrupted by cutting off the power supply between the anode and the cathode; micro-cells are formed between A, M and the H⁺ ions, such that a depolarisation corresponding to the conversion step C° occurs, with H₂ being produced and M and A being dissolved into M^m+ and A^a+ at the electrode, which acts as a cathode in step E ¹; - the H₂ produced is collected. The invention also relates to devices for implementing such a production method and a kit comprising one of said devices and the electrolyte components.

Description

ELECTROCHEMICAL PROCESS FOR THE PRODUCTION OF GASEOUS HYDROGEN UNDER PRESSURE BY ELECTROLYSIS AND BY DEPOLARIZATION

Technical area

The field of the invention is that of the electrochemical production of gaseous hydrogen under pressure.

In particular, the invention relates to an electrochemical process for producing gaseous hydrogen by electrolysis and electrochemical conversion of H ⁺ ions to gaseous hydrogen by depolarization.

The invention also relates to a device for the implementation of such a process for producing hydrogen, and a kit comprising the device and all or part of consumables useful in said method.

State of Vart Technical problem

Hydrogen is the cleanest and most efficient fuel for producing energy both in a fuel cell and in an internal combustion engine.

These qualities are particularly valuable for applications of hydrogen as fuel for transport vehicles, in which the hydrogen stored in the vehicle produces kinetic energy by means of an internal combustion engine whose fuel is hydrogen and / or an electric motor powered by an on-board fuel cell consuming hydrogen.

Moreover, the storage of energy in the form of hydrogen under pressure is also particularly advantageous.

Hydrogen is an invisible gas that is odorless and non-toxic. Its consumption in a fuel cell produces only electrical energy and water, while its combustion does not lead to harmful by-products.

The most economical and therefore most widely used method of producing hydrogen is the reforming of natural gas to steam.

The production of hydrogen by electrolysis of water is much more confidential because it is much more expensive.

In this context, hydrogen appears to be the most appropriate energy carrier to support the energy transition, in particular to allow clean mobility as well as energy storage. To do this, hydrogen must be made from electricity and water: these are conventional alkaline or solid electrolyte proton exchange membrane (Proton Exchange Membrane) electrolysis processes, or developing such that high temperature electrolysis. The use of hydrogen in the context of clean mobility requires the ability to store hydrogen under pressure in tanks on board vehicles, at high pressures ranging from 200 to 700 bar.

The conventional method is to compress the gas with a mechanical compressor; it is an expensive operation that requires many maintenance operations.

There are already hydrogen refueling stations for land transport vehicles. This hydrogen can be produced centrally and then distributed to the distribution stations, or even produced directly on the site of the distribution station. On-site production is particularly attractive in terms of logistics

Moreover, from an ecological perspective, it would be interesting if this production of hydrogen on site, but also in a centralized way, is carried out by electrolysis.

But it turns out that the hydrogen pressures hitherto reached at the outlet of the electrolyser are not greater than 80 bars.

Many vain attempts have been made to overcome this ceiling.

Some of these attempts have been to design devices to provide a solution to this technical problem of producing high pressure hydrogen. Such devices are for example described in the following patents US4758322A1, US6153083A1, DE 9115337.9 U. These various known devices have several drawbacks that result from the need to manage not only the power supply of the electrodes, but also a complex fluidics with the electrodes. Inlet outlets for liquids and gases.

These known devices face the constraining factor of having to simultaneously manage the two oxygen and hydrogen gases resulting from the electrolysis, with the imperative requirement to ensure the total separation of the two gases for safety reasons.

To overcome this constraint, patent application US20040211679A1 describes a method of performing electrochemical compression at the output of the electrolyser, in a second apparatus. This technical proposal has the drawback of making the production process more complex, and therefore more expensive. The constraint of simultaneous management of oxygen and hydrogen specific to the electrolysis of water, could be annihilated in the process according to the patent FR2948654B1. This method indeed provides a decoupled electrolysis in two steps. A metal salt (zinc, nickel or manganese) is used in an electrolytic cell to decouple the electrolysis reaction from water in two steps. In a first step, the method makes it possible to store electricity by depositing a metal on the cathode and releasing oxygen at the anode of the electrolytic cell. In a second step, the electrolytic cell operates in battery mode, allowing the dissolution of said metal and the production of hydrogen. This process is used to store electricity and return it as hydrogen.

This decoupling of the production of hydrogen and oxygen is made possible by the use of the intermediate vector consisting of the redox ion / metal pair.

The decoupling of G electrolysis of water is also described in the following patent applications:

CN105734600A (electrolysis in basic medium). The intermediate vector is a Redox pair E ° (Ni0 ₂ / Ni (OH) ₂ ) = -0.49 V between that of the water [E ° (0 ₂ / OH) = 0.4 V in basic medium] and that of hydrogen [E (H ₂ O / H ₂ ) = -0.83 V in basic medium] WO2013068754A1 & WO2016038214A1 (electrolysis in an acidic medium).

This decoupling of the process,

on the one hand, in an electrolysis step leading to an energy storage in chemical form and, on the other hand, in a conversion step of this stored electrochemical energy into an electrical energy with concomitant release of hydrogen gas,

allows to collect hydrogen gas under higher pressure than that obtained with the devices of the prior art mentioned above.

However, the industrialization and rationalization of gaseous hydrogen production under pressure, require substantial improvements in terms of pressure achievable without sacrificing simplicity, economy and security constraints.

Objectives of the invention

In these circumstances, the present invention aims to satisfy at least one of the objectives set out below.

"One of the essential objectives of the present invention is to provide an improved method of producing gaseous hydrogen gas under electrochemically pressure, in a decoupled manner, to achieve high hydrogen gas pressures for example> 80 bar. "One of the essential objectives of the present invention is to provide an improved method of producing gaseous hydrogen gas electrochemically under pressure, without decoupling, and without sacrificing industrial safety requirements.

"One of the essential objectives of the present invention is to provide an improved and economical process for the electrochemically generated production of gaseous hydrogen gas in a decoupled manner.

"One of the essential objectives of the present invention is to provide an improved method of producing gaseous hydrogen under pressure electrochemically, decoupled and in compliance with environmental constraints.

"One of the essential objectives of the present invention is to provide an improved method for the production of gaseous hydrogen gas under electrochemical pressure in a decoupled manner and whose implementation is possible in a non-industrial and non-controlled environment. specialized operators, that is to say on a gaseous hydrogen distribution site, completely autonomously.

"One of the essential objectives of the present invention is to provide an industrial device, reliable, efficient, economical and robust, for the implementation of the method as referred to in one of the above objectives.

Brief description of the invention

These objectives, among others, are achieved by the present invention, which concerns, first of all, an electrochemical process for producing gaseous hydrogen under pressure, characterized in that it essentially consists in implementing, in at least one enclosure, at least one electrolysis step É of an electrolyte comprising at least one solvent, preferably aqueous, this electrolysis step É converting electrical energy into chemical energy, with production of gaseous oxygen in an enclosure E and least one step of conversion C ° of this chemical energy into a redox energy with production of hydrogen gas in a closed chamber C °, identical or different, preferably identical, to the enclosure E ^? ;

in which:

The electrolyte comprises ions M ^{m +} , M corresponding to the redox couple (M ^{m +} / M), and ions A ⁺ of at least one depolarization additive A corresponding to a redox couple (A ^{a +} / A) with: the absolute value of the overvoltage of the hydrogen evolution reaction on the metal M is greater than the difference E _th (H ⁺ / H ₂ ) -E _th (M ^{m +} / M) in an acid medium or E _th (H ₂ 0 / H ₂ ) - E _th (M ^{m +} / M) in basic medium;

E _th (A ^{a +} / A) <E _th (H ⁺ / H ₂ ) in an acidic medium;

E _th (A ^{a +} / A) <E _th (H ₂ O / H ₂ ) in basic medium;

m is an integer; preferably between -5 and 5, and more preferably between -4 and 4;

a is an integer; preferably between -5 and 5, and more preferably between -4 and 4;

the absolute value of the overvoltage of the hydrogen evolution reaction on the metal A is less than the difference E _th (H ⁺ / H ₂ ) - E (M ^{m +} / M) in an acid medium or E _th (H ₂ 0 / H ₂ ) - E _th (M ^{m +} / M) in basic medium;

-> Electrolysis step E ^? is started by current supply between the anode and the cathode;

-> A ^{a +} and M ^{m +} are respectively deposited as A and M on the cathode during the electrolysis step E ^? and gaseous oxygen is evolved at the anode;

-> Electrolysis step E ^? is stopped by cutting off the power supply between the anode and the cathode;

-> local depolarization effects appear between A, M and H ⁺ ions, said effects leading to the production of hydrogen gas and dissolution of M and A in M ^{m +} and A ^{a +} to the electrode that plays the role cathode during step E ¹ ; which corresponds to the conversion step C °;

The gaseous hydrogen thus produced is collected, preferably under a pressure p ^Hyd ; -> This hydrogen gas thus collected is possibly stored outside the enclosure.

The process according to the invention is particularly efficient and advantageous in that it consists in carrying out an electrochemical compression integrated into the electrolysis of an electrolyte, preferably aqueous, and, more preferably still water, so as to directly produce water. hydrogen at a very high pressure, decoupled by means of an intermediate vector consisting of a Redox couple (M ^{m +} / M) in the presence of the depolarizing agent (A ^{a +} / A), in 2 independent steps: electrolysis with evolution of oxygen then oxidation of M to M ^{m +} and of A to A ⁺ with release of hydrogen. The simplification thus provided and the economic gains that go hand in hand constitute a significant technological advance, compared to the state of the art in this field of electrochemically producing hydrogen gas.

Advantageously, M is a metal compound consisting of at least one metal and / or at least one compound based on at least one metal, for example a metal oxide.

The process according to the invention makes it possible to reach hydrogen pressures greater than 80 bar. This is a minimum to reach to consider large-scale applications in the field of mobility (transport).

In a context of industrial production, it is also essential that this manufacture of pressurized hydrogen be done in the strictest respect of the safety rules. In this respect, one of the key points is the explosiveness of the gaseous hydrogen / oxygen mixture.

By these innovative arrangements, the method according to the invention and more generally the system according to the invention which comprises the method and the device, perfectly integrates this safety constraint.

In another of its aspects, the present invention relates to a device for implementing the method.

This device comprises:

a) at least one closed enclosure É intended to contain at least one electrolyte; b) at least one cathode intended to be immersed in the electrolyte;

c) at least one anode intended to be immersed in the electrolyte;

d) a power supply connected to the cathode and the anode;

e) at least one gas evacuation duct equipped with at least one valve, this evacuation duct preferably subdivided, on the one hand, into at least one duct intended for the evacuation of the gaseous oxygen possibly in mixture with hydrogen gas and, secondly, in at least one conduit for the evacuation of hydrogen gas; each of these ducts being equipped with at least one valve; f) possibly means for increasing the G / L interface;

g) optionally means for circulating the electrolyte in the enclosure; h) optionally means for heating the electrolyte in the enclosure. This simple and effective device has particular interest to include one or more enclosures each comprising at least one electrochemical cell including only, preferably, a cathode and an anode. This simplicity makes it possible to consider relatively relatively the multiplication of unit electrochemical cells in order to produce large quantities of hydrogen in a minimum of space.

Another object of the invention relates to a kit for carrying out the method comprising a device and at least a part of the components for the preparation of the electrolyte or electrolytes intended to be contained in the enclosure or the enclosures of the device .

Definitions

Throughout this presentation, any singular denotes indifferently a singular or a plural.

The definitions given below as examples may be used to interpret this presentation:

• "electrolyte": aqueous solution or ionic liquid containing ions A ⁺ , M ⁺ ,

Y ^{y +} Y ^v jq ⁺ , OH

• "acid electrolyte": pH <7 (+/- 0.1)

• "basic electrolyte": pH> 7 (+/- 0.1)

• "E °": standard potential. The standard potentials E ° referred to in this presentation are all measured under the same conditions (reference, temperature, concentrations).

• "Efi": thermodynamic potential of the electrochemical reaction.

• "E": non-equilibrium potential of the electrochemical reaction, equal to the addition of the thermodynamic potential and the overvoltage of the electrochemical reaction.

• "decoupled": qualifies the realization of the process according to 2 separate and independent stages; the first of these steps being an electrolysis leading to a reduced deposition of a material at the cathode, deposit constituting an electrochemical energy storage, while the ^2nd step is a step of oxidizing materials deposited to the cathode electrolysis with production of hydrogen gas by reduction of H ⁺ ions;

• "about" or "substantially" means plus or minus 10%, or within plus or minus 5%, based on the unit of measurement used; • "between Z1 and Z2" means that one and / or other of the terminals Z1, Z2 is included or not in the interval [Z1, Z2]

Detailed description of the invention

PROCESS

The electrochemical compression specific to the process according to the invention is integrated in a decoupled and independent 2-step process, namely, on the one hand, electrolysis É of the electrolyte (preferably an aqueous solution), and, d on the other hand, an oxidation reaction of the species deposited at the cathode during the electrolysis, concomitantly with the production of hydrogen by reduction of the H ⁺ ions contained in the electrolyte.

The invention uses, inter alia, the property of metals or alloys M selected according to the invention, to block the evolution of hydrogen, when electrolysis of their salts M ^{n +} . It is the phenomenon called hydrogen overvoltage, leading to an electrochemical state out of equilibrium.

The electrolysis step E of the electrolyte carried out in the presence of these salts M ^{n +} leads to an oxygen evolution at the anode, a deposit of the metal M at the cathode and an energy accumulation corresponding to the non-equilibrium state.

During step C ° of electrochemical conversion, a return to equilibrium makes it possible to release hydrogen. The metal (or alloy) M is oxidized to the salt of M ^{n +} . The hydrogen gas is evolved by releasing the energy accumulated during the electrolysis step E.

One of the keys to the present invention is the addition of chemical elements in the form of ions or A ⁺ molecules in the electrolyte before the electrolysis step E. This depolarization additive formed by the Redox couple (A ^{a +} / A) makes it possible to achieve the return to equilibrium proper to the step C ° and thus this evolution of hydrogen during this step C °, without using an electrode. hydrogen. This implementation of at least one depolarization additive contributes to the control of the kinetics through the concentrations of the ionic species A ^{a +} and M ^{m +} introduced into the electrolyte. The concentrations can be adjusted according to the application.

The intervening mechanism is as follows: in step E1, the ion or molecule A ⁺ is co-deposited in metallic form A with the metal M during step E1. Preferably, step E ^? is stopped when the local depolarization effects appear. Then, in step C °, the local depolarization effects are formed between A, M and the H ⁺ ions, which accelerates the dissolution of the metal M and the evolution of hydrogen. Electrolyte

According to the invention, the electrolyte is preferably an acidic or basic aqueous solution, or an ionic liquid.

According to a preferred embodiment, the electrolyte is an aqueous saline solution further comprising at least one acid or a Bronsted base, the counterion of which is preferably identical to the ion of salt M and / or of A.

The M ⁺ ions of the electrolyte are preferably ions of a single metal M.

According to a remarkable arrangement of the invention, M is a metal, preferably chosen from the group comprising - ideally consisting of -: Zn, Cd, Sn, Ni, Mn, Fe, Pb, Co, Hg, their alloys and their mixtures ; Zn being particularly preferred.

Advantageously, the ions of the metal M are introduced into the electrolyte by at least one precursor, preferably chosen from the group comprising - ideally consisting of -: salts, in particular sulphates, oxides, nitrates, chlorides, citrates, phosphates, carbonates, fluorides, bromides, oxides, aqueous solutions of alkali metal or alkaline earth metal hydroxides and mixtures thereof.

According to the invention, the metal M is chosen so that it can be deposited during the electrolysis step E on the cathode, with the electrolyte in question, with the best possible yield. Preferably, this means that the absolute value of the overvoltage of the hydrogen evolution reaction on the metal M is greater than the difference E _th (H ⁺ / H ₂ ) -E _th (M ^{m +} / M) in an acid medium and unlike E _th (H ₂ 0 / H ₂ ) - E _th (M ^{m +} / M) in basic medium.

The electrolyte also contains A ⁺ ions, preferably a single metal A.

A is different from M. A and M are distinguished from each other not only by their chemical nature but also by the thermodynamic electrochemical potentials E _th of their respective redox pairs, which satisfy the inequalities mentioned above.

In a notable feature of the invention, A is a metal preferably selected from the group consisting of - ideally consisting of - Fe, Co, Sn, Ni, Ta, Mo, W, Pd, Rh, In, Ge, their alloys and their mixtures; Fe and Ni being particularly preferred. In an advantageous variant of the invention, the ions of the depolarization additive A are introduced into the electrolyte by at least one precursor, preferably chosen from the group comprising - ideally consisting of -: salts, in particular sulphates , oxides, cyanates, phosphates, ammonia, nitrates, chlorides, hydrated ions, complex ions, and mixtures thereof; and more preferably still, among the complex ions in oxygenated, cyanurea, ammoniated or fluorosilicic form, and mixtures thereof.

This additive A ^{a +} is a chemical element that meets the following criteria:

-> the thermodynamic potential of the redox couple (A ^{a +} / A) is lower than that of the hydrogen evolution reaction:

E _th (A ^{a +} / A) <E _th (H ⁺ / H ₂ ) in an acidic medium;

E _th (A ^{a +} / A) <E _th (H ₂ O / H ₂ ) in basic medium;

-> the absolute value of the overvoltage of the hydrogen evolution reaction on metal A is less than the difference E ° (H ⁺ / H ₂ ) - E ° (M ^{m +} / M) in acidic medium and unlike E (H ₂ O / H ₂ ) - E (M ^{m +} / M) in basic medium;

Advantageously, the electrolyte is such that the ionic species [in particular H ⁺ , OH] that it contains, other than M & A, are not reduced or oxidized during the two steps of the process. In other words, it means that these species other than M & A do not react electrochemically in a potential window bounded by the voltage of the electrode on which the A / B couple reacts and the voltage of the electrode on which reacts the couple 0 ₂ / H ₂ 0 in acid medium or 0 ₂ / OH in basic medium.

At the beginning of step E ^? ,

M ^{m +} is present in the electrolyte in a concentration range of between 0.1 and 15 mol / ^l , preferably between 0.2 and 10 mol / ^l.

A ^{a +} is present in the electrolyte in a concentration range of between 10 ⁵ and 1 mol.L ¹ , preferably between 10 ⁴ and 10 ¹ mol.L ¹ . Electro-Chimijgue

The electrolysis step E and the conversion step C ° are carried out in at least one electrochemical cell, which comprises an enclosure Et ° containing the electrolyte in which at least one cathode and at least one anode are immersed.

During the electrolysis step E which occurs after current supply of the anode of the cathode, M ^{m +} and A ^{a +} are reduced to M & A and are deposited on the cathode.

Preferably, each enclosure E comprises at least one cathode and at least one anode.

According to an advantageous arrangement of the invention, during the electrolysis step E 1, the DC power supply delivers a current density i (A / m ² ) of between 100 and 5000, preferably 200 and 3000, and more preferably still 400 and 2000.

According to a remarkable characteristic of the invention, the cathode is made from a material allowing the deposition of the metal M with a Faraday yield of at least 30%, preferably at least 50%, this material being of Preferably selected from the group of metals and / or metal alloys, comprising and ideally composed of: Al, Pb and Pb alloys, carbon, nickel, and / or iron materials, stainless steels, and the like. combinations of these materials.

Oxygen gas resulting from the oxidation of water during the electrolysis step E ^? emerges in the vicinity of the anode.

Preferably, the anode is either made from a material selected from the group of metals and / or metal alloys, comprising and ideally composed of: Pb and Pb alloys, in particular Pb-Ag-Ca alloys or Pb-Ag, steels, iron, nickel; and the combinations of these materials, either consists of a dimensionally stable anode Dimensionally Stable Anode (DSA), or at least one oxide.

Varuinje method for increasing the diffusion of dissolved hydrogen

According to an advantageous possibility of the invention, the interface between the undissolved gas phase G and the liquid phase L - hereinafter referred to as the G / L- interface is increased at least during step C °, so as to accelerate the diffusion of the liquid phase to the gaseous phase, dissolved hydrogen which can oversaturate the electrolyte. This provision has the effect of remedying what limits the production of hydrogen gas, namely, on the one hand the solubilization of hydrogen in the electrolyte, in particular in the electrolyte formed by an aqueous solution containing ions as well as H ⁺ or OH ions and, on the other hand, the supersaturation of the electrolyte in dissolved hydrogen.

Advantageously, the increase of the interface is carried out by implementing at least one of the following operations:

(i) the forced circulation, which preferably consists in generating an electrolyte flow in the enclosure E ^ C ° or C °, more preferably, using at least one pump so as to evacuate and renew the gas bubbles present on the electrode or the electrodes and on any roughness of the enclosure E ^ C ° or C °;

(ii) partial decompression which consists in isolating the bottle from the reactor for a certain time; when the pressure in the reactor is sufficiently greater than that of the bottle, the reactor is decompressed in the bottle, creating or increasing the supersaturation of the H ₂ in the electrolyte, thus favoring the germination of the bubbles;

(iii) spraying the electrolyte into fine droplets in the gaseous sky of

(iv) at least one heating, preferably at least one localized heating, of the electrolyte, which advantageously consists in locally reducing the solubility of the dissolved hydrogen gas, thereby promoting the nucleation of bubbles,

(v) diffusion of ultrasound into the electrolyte to generate bubbles,

(vi) at least one depolarization, preferably at least one localized depolarization of the electrolyte, for locally increasing the supersaturation and promoting the formation of bubbles,

(vii) the use of nanoparticles and / or at least one porous nucleating material in the electrolyte, to promote the nucleation of bubbles and to increase the number of bubble germination sites,

(viii) the mechanical agitation of the electrolyte which promotes the nucleation of the bubbles by supplying the energy necessary to counter the surface tension. DEVICE

In another of its aspects, the present invention relates to a preferred device for the first mode of implementation, which comprises:

c) at least one anode intended to be immersed in the electrolyte;

d) a power supply connected to the cathode and the anode;

e) at least one gas evacuation duct equipped with at least one valve, this evacuation duct preferably subdivided, on the one hand, into at least one duct intended for the evacuation of the gaseous oxygen possibly in mixture with hydrogen gas and, secondly, in at least one conduit for the evacuation of hydrogen gas; each of these ducts being equipped with at least one valve;

f) possibly means for increasing the G / L interface;

g) optionally means for circulating the electrolyte in the enclosure; h) optionally means for heating the electrolyte in the enclosure.

KIT

The present invention also relates to a kit for implementing the method. This kit is characterized in that it comprises:

the device according to the invention;

and the components for the preparation of the electrolyte intended to be contained in the enclosure of the device.

This kit which forms a packaging unit for sale, may also include an explanatory note for the implementation of the method using the device and components contained in this kit.

EXAMPLE 1

The description of this example is made with reference to the appended figures in which:

FIG. 1 is a schematic representation of the device for implementing the method according to the invention;

FIG. 2 is a straight cross-section along the line II-II of FIG. The device represented in these figures comprises a high-pressure chamber 1, inside which are disposed an anode 2 and a cathode 3, which are immersed in an electrolyte 4. This enclosure 1 is a closed chamber provided with a conduit 5 of gas outlet, which conduit is subdivided into a pipe 6 for evacuation of hydrogen gas and a pipe 7 for evacuation of gaseous oxygen. Each duct 6,7 is equipped with a valve 8,9, respectively H ₂ valve and 0 ₂ valve, allowing the independent extraction of these 2 gases out of the chamber 1 high pressure.

The anode 2 and the cathode 3 are connected to a DC generator 10, able to feed them to induce electrolysis.

Heating means 11 of the chamber 1 are shown schematically in FIG.

The chamber 1, the anode 2, the cathode 3 and the electrolyte 4 form an electrolytic cell. For an industrial production of gaseous hydrogen under pressure, this cell can be multiplied to increase the production capacity.

In the following example, hydrogen was produced at 80 bar in an electrochemical reactor composed of an enclosure 1 and two electrodes (anode 2, cathode 3) bathed in an acidic aqueous solution (electrolyte 4). The two electrodes, each having a surface area of 0.5 m ² , are as follows:

An electrode on which the deposition of the metal (cathode), made of aluminum (reference EN AW 1050A H14 (Al> 99.5%)) takes place;

An electrode on which oxygen (anode) is released, made of lead-silver-calcium alloy (JL Goslar);

Electrolyte 4 is composed of zinc ions - metal M - (concentration 1.5 mol.L ¹ ), sulfuric acid (1.5 mol.L ¹ ) and iron sulfate salt - ion A ⁺⁺ - (8.4 x 10 ⁴ mol.L ¹ ). The temperature is set at 30 ° C.

Electrolyte 4 is prepared by mixing 15.84 kg of sulfuric acid (37.5%, Brenntag) in 7.085 L of deionized water and then adding to this mixture 2.44 kg of ZnO (99.9%, Brenntag). . 4.7 g of iron sulfate heptahydrate (99%, Sigma Aldrich) are finally added to this solution.

Initially, the two electrodes 2 and 3 are immersed in the electrolyte 4. The oxygen valve 9 is open, and the hydrogen valve 8 is closed. During the ^era electrolysis step ^E? , the generator 10 delivers a current density of 595 A / m ² for 2 hours, which makes it possible to deposit 653 g of metal M: zinc on the cathode (with a yield of 90%). At the same time, the iron (depolarization additive A) co-deposits with the cathode 3. The oxygen leaves the chamber 1 via the outlet duct 5 and the duct 7 whose valve 9 is in the open position.

In the second step C °, the power supply 10 is stopped and the hydrogen begins to form. The H ₂ gas leaving enclosure 1 initially contains oxygen and hydrogen; this mixture is sent via the outlet pipe 5 and the pipe 7 whose valve 9 is in the open position, while the valve 8 of the pipe 6 to H ₂ is closed, in a capacity that allows this mixture to be diluted with another gas (argon for example).

A sensor 0 ₂ located in the pipe 7 allows to measure in real time the content of O ₂ in the gas. When it no longer contains oxygen, the valve 9 is closed. The pressure of the hydrogen P ^Hyd produced in the chamber 1 increases as and when the generation of the gas. When the desired pressure P ^Hyd is reached, the valve 8 is opened and the hydrogen is sent, via the outlet duct 5 and the duct 6, to a tank not shown in FIG. 1. The pressure P ^Hyd inside of the chamber 1 is measured using a pressure sensor.

The hydrogen evolution rate is 29 g / h / m ² , and it takes 24 hours to produce 20 g of hydrogen at 80 bar.

EXAMPLE 2

An electrochemical cell has been used to produce hydrogen at atmospheric pressure. The cell contains two compartments, separated by a diaphragm made of polyester. The first compartment contains the electrode which acts as a cathode when the ^st step, and a solution called catholyte (1 L). The second compartment contains the electrode which acts as anode during the ^1st stage, and a solution called anolyte (1 L). Two circulation systems, each driven by a pump, make it possible to renew the electrolytes at a circulation speed of 20 mL / min. Description of the operating conditions:

Compartment 1

Catholyte 12 g / L Mn, 150 g / L of (NFD2SO4, 20 mg / L Co

Cathode 316 Stainless Steel, 1 m ²

Cathode current density 485 A / m ²

Compar

Ànoïyte

Anode Alloy PbAg (1 mass.% To g), 0.485 m ²

Operating conditions

Anodic current density 1000 A / m ²

Temperature 40 ° C

Faraday yield 65%

5.5 V cell voltage

Filing time 2 hours

Quantity of manganese 645.75 g

trademark

Quantity of hydrogen produced 23.52 g

When the ^st step, the two electrodes are connected to a power supply which supplies a current of 10.9 A. The manganese is deposited on the cathode, and oxygen is evolved at the anode. Cobalt acts as a depolarizing additive; it is co-deposited with manganese at the cathode. At the end of the ^1st stage, the power supply is cut off and the hydrogen starts to emerge on the stainless steel electrode. At the same time, manganese oxidizes to Mn ²⁺ ions and cobalt to Co ²⁺ ions.

Claims

An electrochemical process for producing hydrogen gas under pressure, characterized in that it essentially consists in using, in at least one chamber, at least one electrolysis step E of an electrolyte comprising at least one solvent, aqueous preference, this electrolysis step E converting electrical energy into chemical energy, with the production of gaseous oxygen in an enclosure E and at least one conversion step C ° of this chemical energy into an oxidation-reduction energy with production hydrogen gas in an enclosure C ° closed identical or different, preferably identical to the enclosure E ^? ;

in which:

The electrolyte comprises ions M ^{m +} , M corresponding to the redox couple (M ^{m +} / M), and ions A ⁺ of at least one depolarization additive A corresponding to a redox couple (A ^{a +} / A) with:

the absolute value of the overvoltage of the hydrogen evolution reaction on the metal M is greater than the difference E _th (H ⁺ / H ₂ ) -E _th (M ^{m +} / M) in an acid medium and the difference E _th (H ₂ O / H ₂ ) - E _th (M ^{m +} / M) in basic medium; E _th (A ^{a +} / A) <E _th (H ⁺ / H ₂ ) in an acidic medium;

E _th (A ^{a +} / A) <E _th (H ₂ O / H ₂ ) in basic medium;

m is an integer; preferably between -5 and 5, and more preferably between -4 and 4

a is an integer; preferably between -5 and 5, and more preferably between -4 and 4

the absolute value of the overvoltage of the hydrogen evolution reaction on the metal A is smaller than the difference E _th (H ⁺ / H ₂ ) -E _th (M ^{m +} / M) in acid medium and the difference E _th (H ₂ O / H ₂ ) - E _th (M ^{m +} / M) in basic medium; -> Electrolysis step E ^? is started by current supply between the anode and the cathode;

-> Electrolysis step E ^? is stopped by cutting off the power supply between the anode and the cathode; -> local depolarization effects appear between A, M and H ⁺ ions, said effects leading to the production of hydrogen gas and dissolution of M and A in M ^{m +} and A ^{a +} to the electrode that plays the role cathode during step E; which corresponds to the conversion step C °;

The hydrogen gas thus produced is collected, preferably at a pressure p ^Hyd ;

-> This hydrogen gas thus collected is possibly stored outside the enclosure.

2. Method according to claim 1 characterized in that:

-> M is a metal, preferably selected from the group consisting of - ideally consisting of -: Zn, Cd, Sn, Ni, Mn, Fe, Pb, Co, Hg, their alloys and mixtures thereof; Zn being particularly preferred;

-> A is a metal, preferably selected from the group consisting of - ideally consisting of - Fe, Co, Sn, Ni, Ta, Mo, W, Pd, Rh, In, Ge, their alloys and mixtures thereof; Fe and Ni being particularly preferred.

3. Method according to claim 1 characterized by at least one of the following provisions:

The ions of the metal M are introduced into the electrolyte by at least one precursor, preferably chosen from the group comprising - ideally consisting of: - salts, in particular sulphates, oxides, nitrates, chlorides, citrates, phosphates, carbonates, fluorides, bromides, oxides, aqueous solutions of alkali metal or alkaline earth metal hydroxides and mixtures thereof.

The ions of the depolarization additive A are introduced into the electrolyte by at least one precursor, preferably chosen from the group comprising, ideally consisting of: salts, in particular sulphates, oxides, cyanates, phosphates, ammonia, nitrates, chlorides, hydrated ions, complex ions, and mixtures thereof; and more preferably still, among the complex ions in oxygenated, cyanurea, ammoniated or fluorosilicic form, and mixtures thereof. The electrolyte is an aqueous saline solution further comprising at least one acid or a Bronsted base whose counterion is preferably identical to the salt M and / or A.

4. Method according to at least one of the preceding claims characterized in that each enclosure E comprises at least one cathode and at least one anode.

5. Method according to at least one of the preceding claims characterized in that the cathode is made from a material for depositing the metal M with a Faraday efficiency of at least 30%, preferably at least 50%, this material being preferably selected from the group of metals and / or metal alloys, comprising -and ideally composed of: Al, Pb and Pb alloys, carbon-based materials, nickel, and / or iron, stainless steels, and combinations of these materials.

6. Method according to at least one of the preceding claims, characterized in that the anode is made of a material selected from the group of metals and / or metal alloys, comprising and ideally composed of: Pb and alloys Pb, especially Pb-Ag-Ca or Pb-Ag alloys; steels, nickel or iron, and the combinations of these materials, either consists of a dimensionally stable anode Dimensionally Stable Anode (DS A), or at least one oxide.

7. Method according to at least one of the preceding claims characterized in that during the electrolysis step E ^, the DC power supply delivers a current density i

(A / m ² ) of between 100 and 5000, preferably 200 and 3000, and more preferably 400 and 2000.

8. Method according to at least one of the preceding claims characterized in that

the interface between the undissolved gas phase G and the liquid phase L - hereinafter referred to as the G / L- interface is increased at least during step C °, so as to accelerate the diffusion of the liquid phase towards the gaseous phase, dissolved hydrogen saturating, or even supersaturating, the electrolyte.

9. Device for implementing the method according to at least one of the preceding claims, characterized in that it comprises: a) at least one closed enclosure É intended to contain at least one electrolyte; b) at least one cathode intended to be immersed in the electrolyte;

c) at least one anode intended to be immersed in the electrolyte;

d) a power supply connected to the cathode (b) and the anode (c);

f) possibly means for increasing the G / L interface;

10. Kit for implementing the method according to at least one of claims 1 to 10 characterized in that it comprises:

the device according to claim 10;