OA21927A - Ionic conductive membrane, method of manufacturing such a membrane. - Google Patents

Abstract

The invention relates to an ionic conductive membrane for an electrochemical device, membrane comprising a layer of a material comprising a ceramic, membrane characterized in that said ceramic comprises Boron Carbide (B4C). The invention also relates to a method for manufacturing a membrane and a cell for an electrochemical device. Application to the electrolysis of water.

Description

DESCRIPTION

Title of the invention: Ionic conductive membrane, method of manufacturing such a membrane, cell comprising such a membrane and installation comprising such a cell

Technical Field

The invention relates to ionic conductive membranes such as those used in particular, but not exclusively, in electrolysers.

Document DI = FR2916906 describes different types of ceramic-based membranes, including membranes containing boron nitride. When used for water electrolysis, such membranes help activate chemical reactions and produce purer hydrogen and oxygen gases.

Description of the invention

The invention provides a new membrane, with improved ionic conduction properties, and with improved chemical, mechanical and conductive characteristics compared to the membranes described in document D1.

More particularly, the invention provides an ionic conductive membrane for an electrochemical device, membrane comprising a layer of a material comprising a ceramic, characterized in that said ceramic comprises Boron Carbide (B4C).

Boron Carbide is a ceramic that has multipolar molecular bonds, thus making it possible to produce a membrane with good conductivity. The membrane comprising Boron Carbide also has greater chemical resistance, particularly in basic environments. The longevity of the membrane is improved to achieve a lifespan of around 4 to 5 years in corrosive environments (for example in potassium hydroxide), in accordance with current requirements for water electrolysis applications in an alkaline environment in particular. Also for water electrolysis applications, with a membrane comprising Boron Carbide, the phenomenon of H2 gases dissolved in the water passing through the membrane (a phenomenon known as "crossover") is less than with known membranes, which makes it possible to obtain purer gases.

The material preferably comprises:

- 60 to 95% by mass of powdered ceramic, ceramic comprising Boron Carbide, and

- 5 to 40% of a polymer binder.

The polymer binder provides the bond between the particles of the ceramic powder. The binder also makes it possible to obtain a membrane impermeable to gases, particularly hydrogen. The crossover phenomenon is further reduced.

The invention also relates to a method of manufacturing a membrane as well as an electrochemical cell comprising a membrane as described above.

The invention finally relates to a water electrolysis installation comprising at least one electrochemical cell as described above.

Brief description of the figures

The invention will be better understood, and other characteristics and advantages of the invention will appear in the light of the following description of examples of implementations of the invention. These examples are given without limitation. The description should be read in conjunction with the appended drawings in which:

- [Fig. I] shows a cell suitable for water electrolysis application

- [Fig. 2] shows a simplified diagram of a water electrolyzer.

Detailed description of embodiments of the invention

As previously stated, the invention relates to an ionic conductive membrane for an electrochemical device, membrane comprising a layer of a material comprising a ceramic, characterized in that said ceramic comprises Boron Carbide (B4C).

The material preferably comprises:

- 60 to 95% by mass of powdered ceramic comprising Boron Carbide, and - 5 to 40% by mass of a polymer binder.

The ceramic powder can be pure Boron Carbide powder. The ceramic powder can also be a mixture of Boron Carbide powder and Boron Nitride powder. The presence of Boron Nitride improves the membrane manufacturing process because Boron Nitride has a greater binding affinity with polymer binders. Boron Nitride is also a dry lubricant that facilitates the implementation of the membrane and can give it more mechanical flexibility. To maintain the chemical and durability properties of Boron Carbide membranes, however, the Boron Nitride must be limited. Thus, among the membranes made from a powder mixture, the most effective membranes were obtained for a quantity of Boron Carbide greater, by mass, than a quantity of Boron Nitride.

The polymer binder used can be:

- a polytetrafluoroethylene (PTFE), or

- a polyether sulfone (PES), or

- a polyether sulfone derivative such as a sulfonated polyether sulfone (PESS) or a chlorinated polyether sulfone amine (PESS-C1-NH2), or

- a mixture of polytetrafluoroethylene (PTFE), polyether sulfone (PES) and/or a polyether sulfone derivative.

With a polytetrafluoroethylene (PTFE) polymer binder, the best results were obtained with a binder quantity of between 5% and 25% by mass (of the finished material). PTFE is chosen for its exceptional resistance to strongly oxidizing agents such as pure oxygen under pressure.

With a polymer binder of the polyether sulfone (PES) type, of a polyether sulfone derivative type such as a sulfonated polyether sulfone (PESS) or a chlorinated amino polyether sulfone (PESS-C1-NH2), or a polymer blend comprising polytetrafluoroethylene (PTFE), polyether sulfone (PES) and/or a polyether sulfone derivative, the best results have been obtained with a binder quantity of between 15% and 40% by mass (of the finished material). PES and its derivatives are chosen for their best suitability for large-scale membrane manufacturing processes. To produce a membrane as described above, a process according to the invention essentially comprises the following steps:

- an activation step by dispersing a quantity of ceramic powder in a basic solution, for example a potassium hydroxide KOH solution, and

- a step of adding a binding polymer to the solution, in an amount between 5 and 40% by mass.

During the activation step, the solution is stirred for 1 H to 24 H. The activation step by soaking in a basic solution eliminates the polluting molecular bonds on the dangling bonds of the molecules of the ceramic powder particles. The use of a basic medium makes it possible to obtain a more chemically resistant membrane, thus providing a longer membrane service life, more compatible with current resistance requirements of 4 to 5 years in corrosive environments for applications such as water hydrolysis.

The addition of the binder polymer allows the powder particles to be bound together to form a membrane without open porosity, impermeable to H2 gas dissolved in the electrolyte water.

Depending on the polymer binder used and the quantity of binder used, the mixing of the polymer binder can be carried out by stirring for a few minutes to a few hours. Also, the mixing can be carried out in a temperate atmosphere around 40° to 60° to facilitate mixing.

The process may also include a step of shaping the mixture.

According to one embodiment, in particular in the case of a mixture comprising PES, the tumbling step may comprise a step of casting the mixture onto a support, for example a glass plate. If necessary to facilitate casting, the casting step may be preceded by a step of adding a solvent such as water or ethanol, to adjust the viscosity of the mixture and make the mixture sufficiently liquid to allow casting. The tumbling step may then be followed by a drying step to remove the solvent and form the polymer network (crosslinking). This embodiment is particularly suitable for large-scale membrane manufacturing.

According to another embodiment, in particular in the case of a mixture comprising PTFE, the tonning step may comprise one or more lamination steps, each lamination step comprising a rolling step and a folding step carried out successively. The lamination step(s) make it possible to fold and connect the long carbon chains of the PTFE polymer binder so as to form a network inside which the ceramic powder particles are trapped. Depending on the consistency of the mixture, the lamination step(s) may be preceded by a filtering step and/or a drying step to obtain a paste, which is flexible but not liquid.

According to yet another embodiment, the step of shaping the mixture may comprise a step of hot extrusion of the mixture, at a temperature of the order of 120° to 180°, preferably 150°. If necessary, the extrusion step may be followed by a lamination step.

Finally, particularly if a flat membrane is desired, the process may include a final rolling step.

For example, the membranes used in water electrolysis installations generally have a thickness of around 0.2 mm to 0.4 mm.

The membrane according to the invention as described above can be used to produce an electrochemical cell comprising in particular

- a 30 anode

I

- a cathode 20, and

- between the anode and the cathode, a membrane l 0 as described above.

Figure 1 shows a diagram of a known cell for a water electrolysis plant for the production of hydrogen H2 and oxygen O2 gas. Figure 2 shows a schematic diagram of a membrane water electrolysis plant. The membrane 10 divides a bath in two, a bath comprising a mixture of water and electrolyte. The cathode 20 and the anode 30 are positioned on either side of the membrane and are connected respectively to the negative and positive terminals of an electrical energy source. The membrane 10 allows good separation of the hydrogen gas produced on the cathode and the oxygen gas produced on the anode. The cathode and the anode are metallic, for example nickel, stainless steel or metal oxides, particularly on the anodic side. Nickel and stainless steel form oxides on the surface which are catalysts for the release of oxygen. 316L stainless steel is particularly effective thanks to its molybdenum content.

Additionally, to improve the chemical reactions, layers 40, 50 of catalysts can be deposited on both sides of the membrane, between the cathode and the membrane on the one hand, between the anode and the membrane on the other hand. Also, layers of catalyst can be deposited on the anode and/or the cathode. The layers of catalyst can comprise nickel powder. The catalyst materials used can also be different for the membrane and for the electrodes.

A single cell is shown in Figure 1. However, in practice, an industrial installation may comprise several cells, or even a hundred cells.

Claims (13)

l. Ionic conductive membrane (10) for an electrochemical device, membrane comprising a layer of a material comprising a ceramic, membrane characterized in that said ceramic comprises Boron Carbide (B4C). 2. Membrane according to claim 1 in which the material comprises: - 60 to 95% by mass of powdered ceramic comprising Boron Carbide, and - 5 to 40% by mass of a polymer binder. 3. Membrane according to claim 2 in which the ceramic powder comprises: - Boron Carbide, or - a mixture of Boron Carbide and Boron Nitride comprising a quantity of Boron Carbide greater, by mass, than a quantity of Boron Nitride. 4. Membrane according to one of claims 2 to 3 in which the polymer binder is: - a polytetrafluoroethylene (PTFE) type polymer, or - a polyether sulfone (PES) type polymer, - a polyether sulfone derivative type polymer such as a sulfonated polyether sulfone (PESS) or a chlorinated amino polyether sulfone (PESS-O-NH2), or - a mixture of polytetrafluoroethylene (PTFE), polyether sulfone (PES) and! or a polyether sulfone derivative. 5. Membrane according to claim 4 in which the polymer binder is a polytetrafluoroethylene (PTFE) type polymer, in an amount of between 5% and 25% by mass. 6. Membrane according to claim 4 in which the polymer binder is a polyether sulfone (PES) type polymer, a polyether sulfone derivative type polymer such as a sulfonated polyether sulfone (PESS) or a chlorinated amino polyether sulfone (PESS-C1-NH2), or a mixture of polymers comprising polytetrafluoroethylene (PTFE), polyether sulfone (PES) and/or a polyether sulfone derivative, polymer binder in an amount of between 15% and 40%. 7. Method for manufacturing an ionic conductive membrane according to one of the preceding claims, method comprising: - an activation step by dispersing a quantity of ceramic powder in a basic solution, for example a potassium hydroxide solution, said ceramic powder comprising boron carbide, __i - a step of adding a polymer binder to the solution to obtain a mixture, and - a step of tonning the mixture. 8. Method according to claim 7. in particular suitable for a mixture comprising polyether sulfone (PES) or a polyether sulfone derivative, method in which the shaping step comprises a step of casting the mixture onto a support, for example a glass plate and a drying step. 9. Method according to the preceding claim in which, in the shaping step, the casting step is preceded by a step of adding a solvent. 10. Method according to claim 7, in particular suitable for a mixture comprising polytetrafluoroethylene (PTFE), method in which the shaping step comprises at least one lamination step, comprising a rolling step and a folding step carried out successively. I l. Method according to the preceding claim in which, in the shaping step, the laminating step is preceded by a filtering step and/or a drying step to obtain a paste. 12. Method according to one of claims 8 to 11 also comprising a final step of rolling the dough. 13. Cell for an electrochemical device, cell comprising: - an anode (30) - a cathode (20) and - between the anode and the cathode, a membrane (10) according to one of claims 1 to 6. 14. Water electrolysis installation comprising at least one cell according to claim 13.