Composite film of polyethersulfone and zirconium oxide particles of formula ZrO2, and its use as an ion-conducting membrane.

Abstract

The invention relates to a composite film of polyethersulfone, poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), and zirconium oxide particles of formula ZrO2, the content of zirconium oxide particles in the composite film being greater than 40% by mass of the composite film. After impregnation with an aqueous solution, the composite film can be used as an ion-conducting membrane, particularly for protons or hydroxide anions, in a fuel cell or electrolyzer.

Description

Title of the invention: Composite film of polyethersulfone and zirconium oxide particles of formula ZrO2, and its use as an ion-conducting membrane.

[0001] The field of the present invention is that of composite films intended to be used as ion-conducting membranes in electrochemical devices such as fuel cells and electrolysers.

[0002] Many composite materials have been proposed for use as ion-conducting membranes in electrochemical devices. The composite materials may consist of polymers in which particles of inorganic materials such as metal oxides are dispersed.

[0003] For example, Vermeiren et al. describe in the document "Hydrogen Power: Theoretical and Engineering Solutions, 179-184, 1998, a porous membrane conducting hydroxide anions, known under the name "Zirfon", prepared from polysulfone and zirconium oxide. The porosity of the membrane results from the use of the phase inversion technique which is described precisely in patent application WO 9315529 and which proves to be quite complex, since it requires the use of several solvents, in particular a solvent for the polysulfone and a non-solvent for the polysulfone, and that of a pore-forming agent, as well as an immersion extraction operation.

[0004] Patent application US 20050106469 describes a method for obtaining a composite film which appears less complex, since it comprises a simple step of mixing a solution of a polyarylene bearing sulfonate functions and a filler, a coating step, followed by a drying step. The filler is chosen from metal oxide hydrates, phyllosilicates and hygroscopic inorganic porous compounds such as silica, zeolites, titanium, aluminum, zirconium or yttrium oxides. When the filler is a hygroscopic inorganic porous compound, it is desirable to use at most 60 parts, preferably at most 30 parts, per 100 parts of functional polyarylene, to preserve the proton transport properties. Despite its apparent simplicity, the process requires the custom synthesis of a polyarylene bearing sulfonate functions which is not a commercially available product.Furthermore, the prepared membrane is only effective for the transport of protons.

[0005] The Applicant has discovered a new process for obtaining a composite film intended to be used as an ion-conducting membrane. The process does not have the disadvantages of the processes mentioned. Indeed, the elementary operations which define are very simple, especially with the use of a single solvent, and the raw materials useful for making the film are all commercially available. Furthermore, the new composite film prepared according to the invention can be used, after its impregnation with an aqueous solution, as an ion-conducting membrane, in particular for protons or hydroxide anions.

[0006] Thus a first object of the invention is a composite film of polyethersulfone, poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), and zirconium oxide particles of formula ZrO2, the content of zirconium oxide particles in the composite film being greater than 40% by mass of the mass of the composite film.

[0007] A second subject of the invention is an ion-conducting membrane which comprises a composite film according to the invention and impregnated with water or an aqueous solution containing an electrolyte.

[0008] A third subject of the invention is a process for preparing a composite film in accordance with the invention.

[0009] A fourth subject of the invention is a process for preparing a membrane according to the invention.

[0010] The invention also relates to a fuel cell which comprises a membrane according to the invention.

[0011] The invention also relates to an electrolyser which comprises a membrane according to the invention. Detailed description of the invention

[0012] The polymers mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, they may also come from the recycling of materials already used, that is to say they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0013] The constituent elements of the composite film according to the invention are polyethersulfone and zirconium oxide.

[0014] Polyethersulfone is, as is well known, poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), the constituent units of polyethersulfone are of formula (Ci2H8O3S). Polyethersulfone is typically a commercially available product, generally in the form of granules, for example from BASF, Solvay, Sumitomo, Goodfellow, under the respective trade names Ultrason® E, Varadel®, Sumikaexcel®. It is used without chemical modification prior to its use in the preparation process of the composite film. The polyethersulfone preferably has a weight-average molar mass (Mw) greater than 5,000 g / mol and less than 500,000 g / mol, more preferably greater than 10,000 g / mol and less than 200,000 g / mol, even more preferably greater than 15,000 g / mol and less than 100,000 g / mol.

[0015] The zirconium oxide particles useful for the purposes of the invention have the chemical structure ZrO2. They are generally spherical or quasi-spherical. They are typically products commercially available, for example, from Sigma-Aldrich, Thermo Fischer Chemicals or from Saint-Gobain (ZirPro®) under the trade names “ZirPro CC”, “ZirPro CS”, “ZirPro CZE” or from Inframat under the trade names “40R-0803CF”, “40R-0801”, “40R-0802”. They are present in the composite film in a content greater than 40% by mass of the mass of the composite film and preferably in a content less than 95% by mass of the mass of the composite film. Advantageously, the content of zirconium oxide particles in the composite film is greater than 50% by mass of the mass of the composite film and less than 95% by mass of the mass of the composite film.Preferably, the zirconium oxide particles have a volume median size, D50, of less than 10 pm. Also preferably, the zirconium oxide particles have a volume median size, D50, of greater than or equal to 1 pm.

[0016] Preferably, the composite film has a thickness of 15 μm to 200 μm. These dimensions are particularly advantageous for use of the composite film in a membrane conducting ions, protons or hydroxide anions, of an electrochemical device such as a fuel cell or an electrolyzer.

[0017] The composite film is typically a non-porous film.

[0018] Preferably, the polyethersulfone constituting the composite film in accordance with the invention is not crosslinked.

[0019] Very preferably, the composite film is a non-porous film in which the polyethersulfone is not crosslinked.

[0020] The composite film is typically prepared by mixing the polyethersulfone and zirconium oxide particles. The mixing can be carried out according to a first variant in the absence of solvent by melting or according to a second variant in the presence of solvent.

[0021] According to the first variant, the method for preparing the composite film comprises an operation of mixing the polyethersulfone and the zirconium oxide particles in a screw machine, followed by extrusion of the mixture. The mixing temperature in the screw machine can vary from 250°C to 350°C.

[0022] According to the second variant, the process for preparing the composite film comprises the following steps a) to f): - a) dissolve the polyethersulfone in dimethyl sulfoxide, DMSO, to form a solution, - b) add the zirconium oxide particles to the solution to obtain a suspension, - c) shake the suspension, - d) depositing the suspension on a support to form a layer, - e) drying the layer on the support to obtain the composite film, - f) peeling the composite film from the support.

[0023] The support is typically in the form of a plate which has a surface on which a layer of the suspension is deposited. The dimensions of this surface are chosen by a person skilled in the art generally according to the desired dimensions of the composite film. They may be comparable to those desired of the composite film or alternatively larger, in which case the step of peeling the composite film from the support may be followed by cutting to obtain the composite film with the desired dimensions. The support may be made of an organic material such as PET (polyethylene terephthalate), PP (polypropylene), PE (polyethylene) or inorganic, in particular metallic material such as aluminum, stainless steel, preferably aluminum.

[0024] In step a), the concentration of the polyethersulfone solution in DMSO is adjusted by a person skilled in the art so that the suspension formed by the mixture of the polyethersulfone solution and the zirconium oxide particles can be cast onto a support at a temperature close to room temperature to form a layer. It preferably varies from 5% to 20% by weight. Step a) is generally carried out at a temperature close to room temperature (23°C), typically from 22°C to 25°C. In step c), the suspension is stirred so as to obtain a suspension in which the zirconium oxide particles are distributed homogeneously.

[0025] Step e) can be carried out in an oven, in a drying cabinet called a fume cupboard, in an ambient atmosphere, in an inert atmosphere such as nitrogen or in a vacuum.

[0026] Typically, at the end of step e), the film is considered dry for a residual DMSO level of less than 5% by mass of the mass of the film, preferably less than 2% by mass of the mass of the film.

[0027] The composite film in accordance with the invention, whether obtained by the first variant of the process or the second variant of the process, is typically a non-porous film in which the polyethersulfone is not crosslinked.

[0028] The membrane, another object of the invention, has the essential characteristic of comprising the composite film in accordance with the invention which is impregnated with water or an aqueous solution containing an electrolyte which is preferably an aqueous solution of a strong acid or a strong base. It is intended to be used in a electrochemical device, such as a fuel cell or an electrolyzer, containing two electrodes, the anode and the cathode, to ensure the transport of ions, in particular protons or hydroxide anions, from one electrode to the other.

[0029] According to a first variant of the invention, the membrane is typically made of a composite film according to the invention which is impregnated with water. When ions resulting from an oxidation-reduction reaction such as those resulting from an electrolysis reaction are in contact with the surface of the composite film impregnated with water, the composite film impregnated with water, in this case the membrane, has the property of conducting the ions. The ions are preferably protons or hydroxide anions.

[0030] According to a second variant of the invention, the membrane is made up of a composite film according to the invention which is impregnated with an aqueous solution of a strong acid or a strong base. When the composite film is impregnated with an aqueous solution of a strong acid, the membrane is a proton-conducting membrane. When the composite film is impregnated with an aqueous solution of a strong base, the membrane is a hydroxide anion-conducting membrane. Suitable strong bases may be potash, sodium hydroxide, preferably potash. Suitable strong acids may be hydrochloric acid, bromic acid, sulfuric acid, nitric acid, preferably sulfuric acid.

[0031] The membrane according to the invention therefore has the advantage of having ion transport properties which can be chosen according to the nature of the ions in the aqueous solution impregnating the composite film or according to the nature of the ions generated during the redox reactions. It also has the advantage of being able to be used both in alkaline conditions and in acidic conditions, in particular in electrochemical devices such as fuel cells and electrolysers.

[0032] The membrane according to the first variant of the invention can be prepared by a process which contains the process steps described for preparing the composite film, which steps are followed by a step which consists of impregnating the composite film with water.

[0033] The membrane according to the second variant of the invention can be prepared by a process which contains the process steps described for preparing the composite film, which steps are followed by a step which consists of impregnating the composite film with an aqueous solution of an electrolyte which is preferably an aqueous solution of a strong acid or a strong base.

[0034] Whether it is the first variant or the second variant for preparing the membrane, the steps of the method described for preparing the composite film are indifferently those implemented in the absence of solvent or in the presence of solvent, respectively described in the first variant and in the second variant for preparing the composite film.

[0035] The impregnation rates are preferably less than 25%, a percentage calculated relative to the mass of the membrane, to minimize the impact of the dimensional change of the membrane on the operation of an electrochemical device such as a fuel cell or an electrolyzer which would contain the membrane.

[0036] According to the invention, the composite film after impregnation with an aqueous solution can be used as an ion-conducting membrane, in particular for protons or hydroxide anions, in a fuel cell or an electrolyser.

[0037] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 17:

[0038] Mode 1: Composite film of polyethersulfone, poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), and zirconium oxide particles of formula ZrO2, the content of zirconium oxide particles in the composite film being greater than 40% by mass of the mass of the composite film.

[0039] Mode 2: Composite film according to mode 1 in which the content of zirconium oxide particles is less than 95% by mass of the mass of the composite film.

[0040] Mode 3: Composite film according to mode 1 or 2 in which the content of zirconium oxide particles is greater than 50% by mass of the mass of the composite film and less than 95% by mass of the mass of the composite film.

[0041] Mode 4: Composite film according to any one of modes 1 to 3 in which the zirconium oxide particles have a volume median size, D50, of less than 10 pm.

[0042] Mode 5: Composite film according to any one of modes 1 to 4 in which the zirconium oxide particles have a volume median size, D50, greater than or equal to 1 pm.

[0043] Mode 6: Composite film according to any one of modes 1 to 5 in which the polyethersulfone has a weight average molar mass greater than 5,000 g / mol and less than 500,000 g / mol.

[0044] Mode 7: Composite film according to any one of modes 1 to 6 in which the polyethersulfone has a weight average molar mass greater than 10,000 g / mol and less than 200,000 g / mol.

[0045] Mode 8: Composite film according to any one of modes 1 to 7 in which the polyethersulfone has a weight average molar mass greater than 15,000 g / mol and less than 100,000 g / mol.

[0046] Mode 9: Composite film according to any one of modes 1 to 8, which composite film has a thickness of 15 pm to 200 pm.

[0047] Mode 10: Composite film according to any one of modes 1 to 9, which film is non-porous.

[0048] Mode 11: Composite film according to any one of modes 1 to 10 in which the po- lyethersulfone is not crosslinked.

[0049] Mode 12: Ion-conducting membrane which comprises a composite film defined in any one of modes 1 to 11 and impregnated with water or an aqueous solution containing an electrolyte.

[0050] Mode 13: Ion-conducting membrane according to mode 12 in which the composite film is impregnated with an aqueous solution of a strong acid or a strong base.

[0051] Method 14: Process for preparing a composite film defined in any one of methods 1 to 11 which comprises the following successive steps a) to f): - a) dissolve the polyethersulfone in dimethyl sulfoxide, DMSO, to form a solution, - b) add the zirconium oxide particles to the solution to obtain a suspension, - c) shake the suspension, - d) depositing the suspension on a support to form a layer, - e) drying the layer on the support to obtain the composite film, - f) peeling the composite film from the support.

[0052] Mode 15: Process for preparing a membrane defined in any one of modes 12 to 13 which comprises the following successive steps: - a) dissolve the polyethersulfone in dimethyl sulfoxide, DMSO, to form a solution, - b) add the zirconium oxide particles to the solution to obtain a suspension, - c) shake the suspension, - d) depositing the suspension on a support to form a layer, - e) drying the layer on the support to obtain the composite film, - f) peeling the composite film from the support, then impregnating the composite film with water or an aqueous solution of an electrolyte which is preferably an aqueous solution of a strong acid or a strong base.

[0053] Mode 16: Fuel cell which comprises a membrane according to mode 12 or 13 or a membrane capable of being obtained by the method according to mode 15.

[0054] Mode 17: Electrolyzer which comprises a membrane according to mode 12 to 13 or a membrane capable of being obtained by the process according to mode 15.

[0055] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative purposes. Examples

[0056] The values ​​of D50 are determined by laser diffraction which makes it possible to determine particle size distribution in volume percentage using a dry granulometer, Mw values ​​by SEC / MALS (size exclusion chromatograph coupled with a differential refractometer and a multi-angle light scattering photometer). Preparation of composite films:

[0057] Composite films F1 to F3 are prepared according to the following procedure: In a beaker, polyethersulfone (Mw 58000 g / mol, “Goodfellow”, commercial reference “SU30-GL-000111”) is dissolved at room temperature with stirring in dimethyl sulfoxide (DMSO) to prepare an 18% by weight solution. To the stirred PESU solution in DMSO, zirconium particles (Zr02, D50 5 μm, supplier Sigma-Aldrich, commercial reference 230693) are added to obtain a homogeneous suspension. The suspension is deposited on a support, an aluminum plate with a deposition surface of 150 mm x 300 mm, to form a layer with a thickness of 500 μm. To remove the DMSO, the support coated with the layer is placed in a fume cupboard on a heating plate at 80°C for 2 hours in ambient atmosphere (air), then at 60°C for at least 12 hours in a vacuum oven. The composite film is considered dry for a residual DMSO content of less than 2% by mass of the composite film. The composite film is recovered by peeling it off the support.The zirconium oxide and PESU contents in the composite film are given in Table 1 and are expressed as a mass percentage relative to the mass of the composite film.

[0058] A film F0 is prepared according to the procedure described for preparing films F1 to F3 with the difference that the step of adding zirconium particles is omitted.

[0059] Table 1: F0 Fl F2 F3 % PESU 100 34 18 9 % ZrO2 0 66 82 91

[0060] Composite films F1 to F3 are all in accordance with the invention. Film F0 is not in accordance with the invention. The thickness of the films varies from 100 to 150 μm.

[0061] Preparation of membranes ML M2 and M3 by impregnation of the respective composite films FL F2 and F3:

[0062] The membranes are prepared according to the following procedure: The composite film is immersed for 24 hours in an aqueous solution of potassium hydroxide (IM) to form the membrane. The membrane is removed from the solution and its surface is wiped. The impregnation rate of the membrane is calculated by the mass difference between the mass of the membrane and the mass of the composite film before its immersion in the solution. The impregnation rate is given in Table 2 as a percentage relative to the mass of the composite film before its immersion in the solution. Membranes M1 to M3 are in accordance with the invention.

[0063] To determine the ionic conductivity of the prepared membrane, its electrochemical impedance across the membrane plane is measured at 23°C, the measurement parameters being an amplitude variation of 10 mV, an applied potential of 0V. The ionic conductivity results are shown in Table 2.

[0064] A control T1 is produced by immersing the film F0 in place of the composite film according to the impregnation procedure described for preparing a membrane. Its ionic conductivity is also measured in the same way as that of membranes M1 to M3. The measurement shows that the control is not conductive.

[0065] Table 2: Composite film / Membrane Fl / Ml F2 / M2 F3 / M3 Impregnation rate (%) * <1 <1 17 Ionic conductivity o (S / cm) 107 104 103

[0066] * 100 x (mass of the membrane - mass of the composite film before its immersion in the solution) / (mass of the composite film before its immersion in the solution).

[0067] The results show that the prepared membranes M1 to M3 are conductive of hydroxide anions unlike the control TL. It is also noted that the ionic conductivity increases with the mass content of zirconium oxide.

[0068] The ionic conductivity of a membrane M4 obtained by impregnation of the composite film F3 in an aqueous solution of sulfuric acid (0.1M) instead of the aqueous solution of potash is also measured and its ionic conductivity is measured under the same conditions as those of the membranes M1 to M3. The membrane M4 is in accordance with the invention. Its ionic conductivity is 10 4 S / cm.

[0069] The ionic conductivity of a control T2 obtained by impregnation of the film F0 in an aqueous solution of sulfuric acid (0.1M) instead of the aqueous solution of potash is also measured and its ionic conductivity is measured under the same conditions as those of the membranes M1 to M3. The control T2 is not conductive.

[0070] The results show that the composite films in accordance with the invention allow ion-conducting membranes to be obtained after impregnation of the composite films with an aqueous solution. The membranes in accordance with the invention can be used in both acidic and alkaline media and allow the transfer of both protons and hydroxide anions depending on the nature of the electrolyte present on the membrane.

[0071] The ionic conductivity property is obtained for relatively high impregnation rates. tively low, which makes it possible to limit changes in the dimension of the membrane and augurs better dimensional stability of an assembly (in English "stack") of a fuel cell or an electrolyzer during its operation, which assembly comprises a membrane according to the invention.

Claims

Claims

1. A composite film of polyethersulfone, poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), and zirconium oxide particles of formula ZrO2, the content of zirconium oxide particles in the composite film being greater than 40% by mass of the mass of the composite film.

2. A composite film according to claim 1 wherein the content of zirconium oxide particles is less than 95% by mass of the mass of the composite film.

3. A composite film according to claim 1 or 2 wherein the zirconium oxide particles have a volume median size, D50, of less than 10 pm.

4. A composite film according to any one of claims 1 to 3 wherein the zirconium oxide particles have a volume median size, D50, greater than or equal to 1 pm.

5. A composite film according to any one of claims 1 to 4 wherein the polyethersulfone has a weight average molar mass greater than 5,000 g / mol and less than 500,000 g / mol, preferably greater than 10,000 g / mol and less than 200,000 g / mol, more preferably greater than 15,000 g / mol and less than 100,000 g / mol.

6. A composite film according to any one of claims 1 to 5, which composite film has a thickness of 15 pm to 200 pm.

7. An ion-conducting membrane which comprises a composite film defined in any one of claims 1 to 6 and impregnated with water or an aqueous solution containing an electrolyte.

8. An ion-conducting membrane according to claim 7 wherein the composite film is impregnated with an aqueous solution of a strong acid or a strong base.

9. A process for preparing a composite film defined in any one of claims 1 to 6 which comprises the following successive steps a) to f): - a) dissolving the polyethersulfone in dimethyl sulfoxide, DMSO, to form a solution, - b) adding the zirconium oxide particles to the solution to obtain a suspension, - c) stirring the suspension, - d) depositing the suspension on a support to form a layer, - e) dry the layer on the support to obtain the composite film, - f) peel off the composite film from the support.

10. A process for preparing a membrane defined in any one of claims 7 to 8 which comprises the following successive steps: - a) dissolving the polyethersulfone in dimethyl sulfoxide, DMSO, to form a solution, - b) adding the zirconium oxide particles to the solution to obtain a suspension, - c) stirring the suspension, - d) depositing the suspension on a support to form a layer, - e) drying the layer on the support to obtain the composite film, - f) peeling the composite film from the support, then impregnating the composite film with water or an aqueous solution of an electrolyte which is preferably an aqueous solution of a strong acid or a strong base.

11. A fuel cell which comprises a membrane according to claim 7 or 8 or a membrane obtainable by the method defined in claim 10.

12. An electrolyser which comprises a membrane according to claim 7 or 8 or a membrane obtainable by the method defined in claim 10.