Composite films of polyethersulfone and zirconium oxide particles with the formula ZrO2 and their applications as ion-conducting membranes

Abstract

This invention relates to a composite film composed of polyethersulfone, i.e., poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), and zirconium oxide particles with the formula ZrO2, wherein the content of zirconium oxide particles in the composite film is 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 in a fuel cell or electrolyzer, particularly a hydroxide anion-conducting membrane or a proton-conducting membrane.

Description

Technical Field

[0001] The present invention pertains to the field of composite films, which are intended to be used as ion-conducting membranes in electrochemical devices such as fuel cells and electrolyzers. Background Technology

[0002] Many composite materials have been proposed for use as ion-conducting membranes in electrochemical devices. These composite materials can consist of polymers, with particles of inorganic materials such as metal oxides dispersed therein.

[0003] For example, Vermeiren et al. described a porous hydroxide anion-conducting membrane called "Zirfon" in their 1998 paper "Hydrogen Power: Theoretical and Engineering Solutions" (pp. 179-184). This membrane was made of polysulfone and zirconium oxide. The membrane's porosity stemmed from the use of a phase transformation technique, described in detail in patent application WO 9315529. This technique proved to be very complex, requiring the use of multiple solvents, particularly solvents and non-solvents for polysulfone, the use of pore-forming agents, and extraction operations via immersion.

[0004] Patent application US 20050106469 describes a method for obtaining a composite film that appears relatively simple, comprising a simple step of mixing a solution of a polyarylene with sulfonate functional groups and a filler, a coating step, and a subsequent drying step. The filler is selected from metal oxide hydrates, foliated silicates, and hygroscopic inorganic porous compounds such as silica, zeolite, or oxides of titanium, aluminum, zirconium, or yttrium. When the filler is a hygroscopic inorganic porous compound, it is desirable to use up to 60 parts, preferably up to 30 parts, of filler per 100 parts of functionalized polyarylene to maintain proton transport properties. Although the method seems simple, it requires the custom synthesis of a polyarylene with sulfonate functional groups, which is not a commercially available product. Furthermore, the prepared membrane is only effective for proton transport. Summary of the Invention

[0005] The applicant has discovered a novel method for obtaining composite films intended for use as ion-conducting membranes. This method overcomes the shortcomings of the methods described above. Specifically, the basic operation of this method is very simple, especially requiring only a single solvent, and the raw materials used to produce the membrane are commercially available. Furthermore, the novel composite film prepared according to this invention, after being impregnated with an aqueous solution, can be used as an ion-conducting membrane, particularly a proton-conducting membrane or a hydroxide anion-conducting membrane.

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

[0007] The second subject of the invention is an ion-conducting membrane comprising a composite film according to the invention, wherein the composite film is impregnated with water or an aqueous solution containing an electrolyte.

[0008] The third subject of this invention is a method for preparing composite films according to the invention.

[0009] The fourth subject of this invention is a method for preparing an ion-conducting membrane according to the invention.

[0010] The present invention also relates to a fuel cell comprising an ion-conducting membrane according to the present invention.

[0011] The present invention also relates to an electrolyzer comprising an ion-conducting membrane according to the present invention. Detailed Implementation Invention Details The polymers mentioned in the specification may be fossil-derived or bio-based. In the latter case, they may be obtained in whole or in part from biomass or from renewable raw materials derived from biomass. Similarly, they may originate from the recycling of used materials, meaning they may be derived in whole or in part from recycling processes or from raw materials that themselves originated from recycling processes.

[0013] The composite film according to the present invention comprises polyethersulfone and zirconium oxide.

[0014] As is well known, polyethersulfone is poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene); the constituent units of polyethersulfone have the formula (C 12 (H8O3S). Polyethersulfone is generally a commercially available product, typically in granular form, such as products from BASF, Solvay, Sumitomo, and Goodfellow, under their respective trade names Ultrason® E, Varadel®, and Sumikaexcel®. Polyethersulfone can be used in composite film preparation methods without prior chemical modification. The weight-average molar mass (Mw) of polyethersulfone is preferably greater than 5000 g / mol and less than 500,000 g / mol, more preferably greater than 10,000 g / mol and less than 200,000 g / mol, and even more preferably greater than 15,000 g / mol and less than 100,000 g / mol.

[0015] The zirconia particles used for the purposes of this invention have the chemical structure ZrO2. They are typically spherical or quasi-spherical. They are generally commercially available products, such as those obtained from Sigma-Aldrich, Thermo Fisher Chemicals, or Saint-Gobain (ZirPro®), under the trade names "ZirPro CC," "ZirPro CS," and "ZirPro CZE"; or products obtained from Inframat, under the trade names "40R-0803CF," "40R-0801," and "40R-0802." They are present in the composite film at a concentration greater than 40% by mass of the composite film, preferably less than 95% by mass. Advantageously, the zirconia particle content in the composite film is greater than 50% by mass and less than 95% by mass of the composite film. Preferably, the volume median particle size D50 of the zirconia particles is less than 10 micrometers. More preferably, the volume median particle size D50 of the zirconia particles is greater than or equal to 1 micrometer.

[0016] Preferably, the thickness of the composite film is between 15 micrometers and 200 micrometers. These dimensions are particularly advantageous for use in ion-conducting membranes (especially proton-conducting membranes or hydroxide anion-conducting membranes) of electrochemical devices (such as fuel cells or electrolyzers).

[0017] Composite films are typically non-porous films.

[0018] Preferably, the polyethersulfone constituting the composite film according to the present invention does not undergo crosslinking.

[0019] Very preferably, the composite film is a non-porous film in which the polyethersulfone has not been cross-linked.

[0020] Composite films are typically prepared by mixing polyethersulfone and zirconium oxide particles. The mixing can be carried out by melt mixing in the absence of solvent, depending on the first variant, or in the presence of solvent, depending on the second variant.

[0021] According to the first variant, the method for preparing the composite film includes mixing polyethersulfone and zirconium oxide particles in a worm gear mill, followed by extrusion of the mixture. The mixing temperature in the worm gear mill can be from 250°C to 350°C.

[0022] According to the second variant, the method for preparing the composite thin film includes the following steps a) to f): - a) Dissolve polyethersulfone in dimethyl sulfoxide (DMSO) to form a solution; - b) Add zirconium oxide particles to the solution to obtain a suspension; - c) Stir the suspension; - d) Depositing the suspension onto a carrier to form a layer; - e) Dry the layers on the carrier to obtain a composite film; - f) Peel the composite film off the carrier.

[0023] The carrier is typically in the form of a plate with a surface on which a layer of suspension is deposited. The dimensions of this surface are usually selected by those skilled in the art based on the desired size of the composite film. The dimensions of the surface can be comparable to or larger than the desired size of the composite film; in this case, after the step of peeling the composite film from the carrier, it can be cut to obtain a composite film of the desired size. The carrier can be made of organic materials (e.g., PET (polyethylene terephthalate), PP (polypropylene), PE (polyethylene)) or inorganic materials (particularly metallic materials, such as aluminum, stainless steel, preferably aluminum).

[0024] In step a), those skilled in the art adjust the concentration of the polyethersulfone solution in DMSO so that the suspension formed by the mixture of the polyethersulfone solution and the zirconium oxide particles can be cast onto the carrier at a temperature close to ambient temperature to form a layer. The concentration is preferably 5% to 20% by weight. Step a) is typically carried out at a temperature close to ambient temperature (23°C), with typical temperatures ranging from 22°C to 25°C. In step c), the suspension is stirred to obtain a suspension in which the zirconium oxide particles are uniformly distributed.

[0025] Step e) can be performed in an oven, drying chamber (also known as a fume hood), under ambient atmosphere, inert atmosphere (such as nitrogen), or vacuum.

[0026] Typically, after step e), the film is considered dry when the residual DMSO content in the film is less than 5% by mass, preferably less than 2% by mass.

[0027] The composite films according to the invention, whether obtained by a first or second variant of the method, are generally non-porous films in which the polyethersulfone is not cross-linked.

[0028] An ion-conducting membrane, another subject of the invention, is essentially characterized by comprising a composite membrane according to the invention impregnated with water or an aqueous solution containing an electrolyte (preferably an aqueous solution of a strong acid or strong base). It is intended for use in electrochemical devices, such as fuel cells or electrolyzers, comprising two electrodes, namely an anode and a cathode, to ensure the transport of ions (particularly protons or hydroxide anions) from one electrode to the other.

[0029] According to a first variant of the invention, the ion-conducting membrane is typically composed of a composite film according to the invention that has been impregnated with water. When ions generated by a redox reaction (e.g., an electrolysis reaction) come into contact with the surface of the water-impregnated composite film, the water-impregnated composite film (in this example, an ion-conducting membrane) acquires the property of conducting ions. These ions are preferably protons or hydroxide anions.

[0030] According to a second variant of the invention, the ion-conducting membrane comprises a composite film according to the invention, 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 ion-conducting membrane is a proton-conducting membrane. When the composite film is impregnated with an aqueous solution of a strong base, the ion-conducting membrane is a hydroxide anion-conducting membrane. Potassium hydroxide and sodium hydroxide, preferably potassium hydroxide, are suitable as strong bases. Hydrochloric acid, bromic acid, sulfuric acid, and nitric acid, preferably sulfuric acid, are suitable as strong acids.

[0031] Therefore, the ion-conducting membrane according to the present invention has the following advantages: its ion transport performance can be selected according to the properties of the ions in the aqueous solution in which the composite membrane is impregnated or according to the properties of the ions generated during the redox reaction. It also has the following advantages: it can be used under both alkaline and acidic conditions, and is particularly suitable for electrochemical devices such as fuel cells and electrolyzers.

[0032] The ion-conducting membrane of the first variant of the present invention can be prepared by a method comprising the steps of the method for preparing a composite film, followed by a step of impregnating the composite film with water.

[0033] The ion-conducting membrane of the second variant of the present invention can be prepared by a method comprising the steps of the method for preparing a composite film, wherein the composite film is impregnated with an aqueous solution of an electrolyte (preferably an aqueous solution of a strong acid or a strong base).

[0034] Whether the first variant or the second variant is used to prepare the ion-conducting membrane, the steps described in the method for preparing the composite film refer to those steps, respectively, performed in the first and second variants for preparing the composite film, either in the absence of solvent or in the presence of solvent.

[0035] The impregnation degree is preferably less than 25% (a percentage calculated relative to the mass of the ion-conducting membrane) to minimize the impact of membrane size variations on the operation of the electrochemical device (e.g., fuel cell or electrolyzer) containing the membrane.

[0036] According to the present invention, after being impregnated with an aqueous solution, the composite film can be used as an ion-conducting membrane in a fuel cell or electrolyzer, particularly a proton-conducting membrane or a hydroxide anion-conducting membrane.

[0037] In summary, the present invention is advantageously implemented according to any one of the following embodiments 1 to 17: Implementation Scheme 1: A composite film composed of polyethersulfone, i.e., poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) and zirconium oxide particles of the formula ZrO2, wherein the content of zirconium oxide particles in the composite film is greater than 40% by mass of the composite film.

[0038] Implementation Scheme 2: According to the composite film of Implementation Scheme 1, the content of the zirconium oxide particles is less than 95% of the mass of the composite film.

[0039] Implementation Scheme 3: The composite film according to Implementation Scheme 1 or 2, wherein the content of the zirconium oxide particles is greater than 50% by mass and less than 95% by mass of the composite film.

[0040] Implementation Scheme 4: The composite film according to any one of Implementation Schemes 1 to 3, wherein the volume median particle size D50 of the zirconium oxide particles is less than 10 micrometers.

[0041] Implementation Scheme 5: The composite film according to any one of Implementation Schemes 1 to 4, wherein the median volume diameter D50 of the zirconium oxide particles is greater than or equal to 1 micrometer.

[0042] Implementation Scheme 6: The composite film according to any one of Implementation Schemes 1 to 5, wherein the number-average molar mass of the polyethersulfone is greater than 5000 g / mol and less than 500,000 g / mol.

[0043] Implementation Scheme 7: The composite film according to any one of Implementation Schemes 1 to 6, wherein the number-average molar mass of polyethersulfone is greater than 10,000 g / mol and less than 200,000 g / mol.

[0044] Implementation Scheme 8: The composite film according to any one of Implementation Schemes 1 to 7, wherein the number-average molar mass of polyethersulfone is greater than 15,000 g / mol and less than 100,000 g / mol.

[0045] Implementation Scheme 9: The composite film according to any one of Implementation Schemes 1 to 8, wherein the thickness of the composite film is 15 micrometers to 200 micrometers.

[0046] Implementation Scheme 10: The composite film according to any one of Implementation Schemes 1 to 9, wherein the film is non-porous.

[0047] Implementation Scheme 11: A composite film according to any one of Implementation Schemes 1 to 10, wherein the polyethersulfone is not crosslinked.

[0048] Implementation Scheme 12: An ion-conducting membrane comprising a composite film as defined in any one of Implementation Schemes 1 to 11, wherein the composite film is impregnated with water or an aqueous solution containing an electrolyte.

[0049] Implementation Scheme 13: The ion-conducting membrane according to Implementation Scheme 12, wherein the composite film is impregnated with an aqueous solution of a strong acid or a strong alkali.

[0050] Implementation Scheme 14: A method for preparing a composite thin film as defined in any one of Implementation Schemes 1 to 11, said method comprising the following sequential steps a) to f): - a) Dissolve polyethersulfone in dimethyl sulfoxide (DMSO) to form a solution; - b) Add zirconium oxide particles to the solution to obtain a suspension; - c) Stir the suspension; - d) Depositing the suspension onto a carrier to form a layer; - e) Dry the layers on the carrier to obtain a composite film; - f) Peel the composite film off the carrier.

[0051] Implementation Scheme 15: A method for preparing an ion-conducting membrane as defined in any one of Implementation Schemes 12 and 13, said method comprising the following sequential steps: - a) Dissolve polyethersulfone in dimethyl sulfoxide (DMSO) to form a solution; - b) Add zirconium oxide particles to the solution to obtain a suspension; - c) Stir the suspension; - d) Depositing the suspension onto a carrier to form a layer; - e) Dry the layers on the carrier to obtain a composite film; - f) Peel the composite film off the carrier. The composite film is then impregnated with an aqueous solution of water or an electrolyte, preferably an aqueous solution of a strong acid or a strong alkali.

[0052] Implementation Scheme 16: A fuel cell comprising an ion-conducting membrane according to Implementation Scheme 12 or 13, or an ion-conducting membrane obtainable by the method according to Implementation Scheme 15.

[0053] Implementation Scheme 17: An electrolytic cell comprising an ion-conducting membrane according to Implementation Scheme 12 or 13, or an ion-conducting membrane obtainable by the method according to Implementation Scheme 15.

[0054] The above and other features of the invention will be better understood by reading the following description of several exemplary embodiments of the invention, which are given by way of illustration.

[0055] Example The D50 value was determined by laser diffraction, which allowed the particle size distribution, expressed as a volume percentage, to be determined using a dry particle size analyzer; the Mw value was determined by SEC / MALS (size exclusion chromatography coupled with a differential refractometer and a multi-angle light scattering spectrophotometer).

[0056] Preparation of composite thin films: Composite films F1 to F3 were prepared according to the following procedure: In a beaker, polyethersulfone (Mw 58,000 g / mol, "Goodfellow", trade number "SU30-GL-000111") was dissolved in dimethyl sulfoxide (DMSO) at ambient temperature with stirring to prepare an 18 wt% solution. Zirconium particles (ZrO2, D50 5 μm, supplier Sigma-Aldrich, trade number 230693) were added to the stirred solution of PESU in DMSO to obtain a homogeneous suspension. The suspension was deposited onto a support (an aluminum plate with a deposition surface of 150 mm × 300 mm) to form a layer with a thickness of 500 μm. To remove DMSO, the support coated with this layer was placed on a heated plate in a fume hood at 80°C for 2 hours under ambient atmosphere (air), and then placed in a vacuum oven at 60°C for at least 12 hours. The composite film was considered dry when the residual DMSO content in the composite film was less than 2 wt% of the composite film. The composite film was peeled off from the carrier, thereby recovering the composite film. The contents of zirconium oxide and PESU in the composite film are shown in Table 1, expressed as a mass percentage relative to the mass of the composite film.

[0057] Thin film F0 is prepared according to the procedures described in thin film preparation F1 to F3, except that the step of adding zirconium particles is omitted.

[0058] Table 1: Composite films F1 to F3 all conform to this invention. Film F0 does not conform to this invention. The film thickness is 100 micrometers to 150 micrometers.

[0059] Ion-conducting membranes M1, M2, and M3 were prepared by impregnating their respective composite films F1, F2, and F3: The ion-conducting membrane was prepared according to the following procedure: The composite film was immersed in a 1 M potassium hydroxide aqueous solution for 24 hours to form an ion-conducting membrane. The ion-conducting membrane was then removed from the solution and its surface was wiped. The degree of immersion of the ion-conducting membrane was calculated as the difference between the mass of the ion-conducting membrane and the mass of the composite film before immersion. The degree of immersion is shown in Table 2 as a percentage of the mass of the composite film before immersion. Ion-conducting membranes M1 to M3 conform to the present invention.

[0060] To determine the ionic conductivity of the prepared ion-conducting membrane, its electrochemical impedance along the membrane plane was measured at 23 °C, using an amplitude change of 10 mV and an applied potential of 0 V. The ionic conductivity results are shown in Table 2.

[0061] According to the impregnation procedure described for preparing ion-conducting membranes, control example T1 was prepared by immersion using thin film F0 instead of the composite film. The method for measuring its ionic conductivity was the same as that used for ion-conducting membranes M1 to M3. The measurement results showed that the control example had no conductivity.

[0062] Table 2: *100×(mass of ion-conducting membrane - mass of composite film before immersion in solution) / (mass of composite film before immersion in solution).

[0063] The results showed that, unlike control example T1, the prepared ion-conducting membranes M1 to M3 were conductors of hydroxide anions. It was also noted that the ionic conductivity increased with increasing zirconium oxide mass content.

[0064] The ionic conductivity of ion-conducting membrane M4, obtained by immersing composite membrane F3 in an aqueous sulfuric acid solution (0.1 M) instead of an aqueous potassium hydroxide solution, was also measured under the same conditions as those for ion-conducting membranes M1 to M3. Ion-conducting membrane M4 conforms to the present invention. Its ionic conductivity is 10. -4 S / cm.

[0065] The ionic conductivity of control example T2, obtained by immersing the composite film F0 in an aqueous sulfuric acid solution (0.1 M) instead of an aqueous potassium hydroxide solution, was also measured under the same conditions as those for ion-conducting membranes M1 to M3. Control example T2 showed no conductivity.

[0066] The results show that the composite film according to the invention can be used to obtain an ion-conducting membrane after impregnation with an aqueous solution. The ion-conducting membrane according to the invention can be used in both acidic and alkaline media, and allows the transport of both protons and hydroxide anions, depending on the properties of the electrolyte in the presence of the ion-conducting membrane.

[0067] The property of ionic conductivity can be obtained at a relatively low degree of impregnation, which makes it possible to limit the size variation of the membrane, and this indicates that fuel cell stacks or electrolyzer stacks including the ion-conducting membrane according to the invention have improved dimensional stability during their operation.

Claims

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

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

3. The composite film according to claim 1 or 2, wherein, The volume median particle size D50 of the zirconium oxide particles is less than 10 micrometers.

4. The composite film according to any one of claims 1 to 3, wherein, The median volume diameter (D50) of the zirconium oxide particles is greater than or equal to 1 micrometer.

5. The 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, and more preferably greater than 15,000 g / mol and less than 100,000 g / mol.

6. The composite film according to any one of claims 1 to 5, wherein the thickness of the composite film is from 15 micrometers to 200 micrometers.

7. An ion-conducting membrane comprising a composite film as defined in any one of claims 1 to 6, wherein the composite film is impregnated with water or an aqueous solution containing an electrolyte.

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

9. A method for preparing a composite thin film as defined in any one of claims 1 to 6, the method comprising the following sequential steps a) to f): - a) Dissolve polyethersulfone in dimethyl sulfoxide (DMSO) to form a solution; - b) Add zirconium oxide particles to the solution to obtain a suspension; - c) Stir the suspension; - d) Depositing the suspension onto a carrier to form a layer; - e) Dry the layers on the carrier to obtain a composite film; - f) Peel the composite film off the carrier.

10. A method for preparing an ion-conducting membrane as defined in any one of claims 7 and 8, the method comprising the following sequential steps: - a) Dissolve polyethersulfone in dimethyl sulfoxide (DMSO) to form a solution; - b) Add zirconium oxide particles to the solution to obtain a suspension; - c) Stir the suspension; - d) Depositing the suspension onto a carrier to form a layer; - e) Dry the layers on the carrier to obtain a composite film; - f) Peel the composite film off the carrier. The composite film is then impregnated with an aqueous solution of water or an electrolyte, preferably an aqueous solution of a strong acid or a strong alkali.

11. A fuel cell comprising an ion-conducting membrane according to claim 7 or 8, or an ion-conducting membrane obtainable by the method defined in claim 10.

12. An electrolytic cell comprising an ion-conducting membrane according to claim 7 or 8, or an ion-conducting membrane obtainable by the method defined in claim 10.

Images