METHOD FOR PRODUCING CATALYST-COATED MEMBRANES

Abstract

The invention relates to a method for producing a catalyst-coated polymer membrane for an electrolyser and/or a fuel cell. In a first step, the method preferably comprises the provision of a glass-ceramic substrate. A mesoporous catalyst layer is then preferably synthesized on the glass-ceramic substrate. In a next step, a polymer membrane is preferably pressed onto the glass-ceramic substrate coated with the catalyst layer at a first temperature T.sub.1. This results in a sandwich structure. In a final process step, the sandwich structure is separated, the catalyst layer being separated from the glass-ceramic substrate and adhering to the polymer membrane.

In addition, the invention relates to a polymer membrane which has been produced by the process of the type mentioned at the outset, and to an electrolyser or a fuel cell having such a polymer membrane.

Claims

1. Method for producing a catalyst-coated polymer membrane for an electrolyser and/or a fuel cell comprising the following steps: a) Providing a glass-ceramic substrate; b) Synthesis of a mesoporous catalyst layer on the glass-ceramic substrate; c) Pressing a polymer membrane onto the glass-ceramic substrate coated with the catalyst layer at a first temperature T.sub.1, thereby producing a sandwich structure; d) Separating the sandwich structure, wherein the catalyst layer is separated from the glass-ceramic substrate and adheres to the polymer membrane.

2. Method according to claim 1 characterised in that the glass-ceramic substrate is a vitreous carbon.

3. Method according to claim 1 characterised in that method step c) and method step d) are followed by the following method step: c1) cooling the sandwich structure to a second temperature T.sub.2.

4. Method according to claim 1 characterised in that method step b) comprises the following steps: (i) Preparing a suspension comprising a template, a metal precursor and a solvent; (ii) Applying the suspension to the glass-ceramic substrate so that a suspension film forms on the glass-ceramic substrate; (iii) Drying the suspension film on the glass-ceramic substrate at a temperature T.sub.4 so that the solvent is evaporated within the suspension film and a layer of a catalyst precursor having integrated template structures is obtained; (iv) thermal treatment of the glass-ceramic substrate comprising catalyst precursors at a third temperature T.sub.3 and a calcination time t.sub.3, so that a mesoporous catalyst layer is formed.

5. Method according to claim 1 characterised in that the temperature T.sub.1 is in a range between 80° C. and 800° C., preferably in a range between 200° C. and 600° C. and in particular at 400° C.

6. Method according to claim 1 characterised in that the polymer membrane is pressed onto the glass-ceramic substrate coated with the catalyst layer with a contact pressure p.sub.1 in a range from 100 N/cm.sup.2 to 10,000 N/cm.sup.2, preferably 1000 N/cm.sup.2 bis 3000 N/cm.sup.2 and a time t.sub.1 in a range from 5 s to 300 min, preferably 5 min to 60 min.

7. Method according to claim 3 characterised in that the temperature T.sub.2 corresponds to a temperature below the glass transition point of the polymer membrane and the temperature T.sub.4 is in a range between 18° C. and 80° C. and/or the temperature T.sub.3 is in a range between 350° C. and 700° C., preferably between 350° C. and 600° C., and the calcination time t.sub.3 is in a range between 1 minute and 1440 minutes, in particular 10 minutes.

8. Method according to claim 4 characterised in that the suspension comprises one or more amphiphilic block copolymers.

9. Method according to claim 8 characterised in that the amphiphilic block copolymer is selected from the group comprising: AB-Block Copolymeren (Polyethylenoxid-block-polystyrene (PEO-PS), Polyethylenoxid-block-polymethylmethacrylat (PEO-PMMA), Poly-2-venlypyridin-block-polyallylmethacrylat (P2VP-PAMA), Polybutadien-bock-polyethyleneoxid (PB-PEO), Polyisopren-bock-polydimethylaminoethylmetacrlyt (PI-PDMAEMA), Polybutadien-bock-polydimethylaminoethylmetacrlyt (PB-PDMAEMA), Polyethylen-block-polyethylenoxid (PE-PEO), Polyisobutylen-block-po-lyethylenoxid (PIB-PEO) and Poly(ethylen-co-buty-len)-block-poly(ethylenoxid) (PEB-PEO), Polystyrol-block-poly(4-vinylpyridin) (PS-P4VP), Polyisopren-block-polyethyleneoxid (PI-PEO), Polydimethoxyanilin-block-polystyrol (PDMA-PS), Polyethylenoxid-block-poly-n-utylacrylat (PEO-PBA), Polybutadien-bock-poly(2-vinylpyridin (PB-P2VP)), Polyethylenoxid-block-polylactid (PEO-PLA), Polyethylenoxid-block-polyglycolid (PEO-PLGA), Polyethylenoxid-block-polycaprolacton (PEO-PCL), Polyethylen-block-polyethylenglycol (PE-PEO), Polystyrol-block-polymethylmethacrlyt (PS-PMMA), Polystyrol-block-polyacrylsäure (PS-PAA), polypyrrol-block-polycaprolacton (PPy-PCL), Polysilicon-block-polyetylenoxid (PDMS-PEO), ABA-Block Copolymeren (Polyethylenoxid-block-polybutadien-block-polyethylenoxid (PEO-PB-PEO), Polyethylenoxid-block-polypropylenoxid-block-polyethylenoxid (PEO-PPO-PEO), Polypropylenoxid-block-polyethylenoxid-block-polypropylenoxid (PPO-PEO-PPO), Polyethylenoxid-block-polyisobutylen-block-polyethylenoxid (PEO-PIB-PEO), Polyethylenoxid-block-polybutadien-block-polyethylenoxid (PEO-PB-PEO)), Polylactid-block-polyethylenoxid-block-polylactidd (PLA-PEO-PLA), Polyglycolid-block-polyethylenoxid-block-polyglycolid (PGLA-PEO-PGLA), Polylactid-co-caprolacton-block-polyethylenoxid-block-polylactid-co-caprolacton (PLCL-PEO-PLCL), Polycaprolacton-blockpolytetrahydrofuran-blockpolycaprolacton (PCL-PTHF-PCL), Polypropylenoxid-block-Polyethylenoxid-block-polypropylenoxid (PPG-PEO-PPG), Polystyrol-block-polybutadien-block-polystyrol (PS-PB-PS), Polystyrol-block-polyethylen-ran-butylen-block-polystyrol (PS-PEB-PS), Polystyrol-block-polyisopren-block-polystyrol (PS-PI-PS), ABC-Block Coplymeren (Polyisopren-block-polystyrol-block-polyethyleneoxid (PI-PS-PEO), Polystyrol-block-Polyvinylpyrrolidon-block-polyethyleneoxid (PS-PVP-PEO), Polystyrol-block-poly-2-venylpyridin-block-polyethylenoxid (PS-P2VP-PEO), Polystyrol-block-poly-2-venylpyridin-block-polyethylenoxid (PS-P2VP-PEO), Polystyrol-block-polyacrylsaure-polyethylenoxid (PS-PAA-PEO)), Polyethylenoxid-block-polylactid-block-decan (PEO-PLA-decan), and other amphiphilic polymers (polyethylene oxide alkyl ether (.sub.PEO-Cxx), for example Brij35, Brij56, Brij58) or mixtures thereof, preferably PEO-PB, PEO-PPO, PEO-PB-PEO, PEO-PPO-PEO.

10. Method according to claim 4 characterised in that metal salt or a plurality of metal salts of different metals in each case, or hydrates thereof, are used as the metal precursor.

11. Method according to claim 10 characterised in that the metal salts are selected from the group comprising metal nitrate, metal halide, metal sulfate, metal acetate, metal citrate, metal alkoxide or mixtures thereof.

12. Method according to claim 11 characterised in that the metals contained in the metal precursor are selected from the group comprising alkali metals, preferably lithium, sodium, potassium, rubidium, cesium, alkaline earth metals, preferably magnesium, calcium, strontium, barium, metals of the third main group of the periodic table, preferably boron, aluminum, indium, gallium, thallium, metals of the fourth main group of the periodic table, preferably tin, silicon, germanium, lead, metals of the fifth main group of the periodic table, preferably bismuth, and transition metals, preferably iridium, ruthenium, cobalt, zinc, copper, manganese, cadmium, vanadium, yttrium, zirconium, scandium, titanium.

13. Method according to claim 4 characterised in that water or a C1-C4 alcohol, C2-C4 ester, C2-C4 ether, formamide, acetonitrile, acetone, tetrahydrofuran, benzyl, toluene, dimethyl sulfoxide, dichloromethane, chloroform or mixtures thereof, preferably methanol, ethanol, formamide and/or tetrahydrofuran, are used as solvents.

14. Polymer membrane for an electrolyser and/or a fuel cell, preferably produced by a process according to claim 1, comprising a nanostructured mesoporous catalyst layer.

15. A fuel cell or electrolyser comprising a polymer membrane according to claim 14.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0125] FIG. 1 is a schematic flow diagram of the preferred method for producing a catalyst-coated polymer membrane.

[0126] FIG. 2 shows a graph together with schematic sketches before (A) and after (B) the transfer of a mesoporous catalyst layer onto a circular membrane;

[0127] FIG. 3 SEM representation in comparison with a schematic sketch of mesoporous RuO.sub.x layers, at the time before and after a transfer from a glass-ceramic substrate to the polymer membrane.

[0128] FIG. 4 SEM representation of mesoporous IrO.sub.x layer which have been calcined at different temperatures at the time before and after transfer from a glass-ceramic substrate to the polymer membrane.

[0129] FIG. 5 shows a comparison of a transferred mesoporous IrO.sub.x layer with a conventional IrO.sub.x layer produced on Nafion membranes with similar geometric Ir loads.

[0130] FIG. 6 shows a diagram of the electrocatalytic activity of a catalyst-coated membrane with a templateized mesoporous iridium oxide catalyst produced by the preferred process according to the invention in comparison with a catalyst-coated membrane with a commercial Ir catalyst produced by a spraying method.

DETAILED DESCRIPTION OF THE FIGURES

[0131] FIG. 1 illustrates, in a schematic flow diagram, a preferred method for producing a catalyst-coated polymer membrane for an electrolyser and/or a fuel cell. The method is preferably to be subdivided into two sequences. On the one hand (outlet A), a mesoporous catalyst layer is synthesized on a glass-ceramic substrate, particularly preferably a vitreous carbon, and on the other hand (outlet B), the mesoporous catalyst layer is transferred to the polymer membrane.

[0132] In a first step of run-off A, a homogeneous suspension is prepared, the suspension preferably comprising a metal precursor (for example Ir(OAc).sub.3, a solvent (for example EtOH) and a template forming micelles (for example 10k-Pb; PEO-PB-PEO). In a next step, the suspension is applied to a glass-ceramic substrate, particularly preferably a vitreous carbon, and calcined in air, so that a mesoporous catalyst layer is formed.

[0133] In run-off B, a polymer membrane is pressed onto the glass-ceramic substrate with the mesoporous catalyst layer present thereon at an elevated temperature (hot pressing process). Finally, the polymer membrane is separated from the glass-ceramic substrate, the catalyst layer adhering to the polymer membrane.

[0134] The sequence of representations shown in FIG. 2 shows a preferred sequence of the method for producing a catalyst-coated polymer membrane. In particular, a graphical representation together with schematic sketches before (A) and after (B) of the transfer of a mesoporous catalyst layer to a circular membrane is illustrated. A vitreous carbon is provided with a mesoporous RuO.sub.x catalyst layer. Subsequently, a Nafion membrane is pressed onto the vitreous carbon comprising the catalyst layer, the catalyst layer adhering to the membrane after the separation of the pressed composite.

[0135] FIG. 3 shows an SEM representation (scanning electron microscope) in a comparison with a schematic sketch of mesoporous RuO.sub.x layers, at the time before and after a transfer from a glass-ceramic substrate to the polymer membrane. FIG. 3 shows the retention of the mesopore morphology during the preferred process sequence, in particular after the transfer of the catalyst layer to the polymer membrane.

[0136] FIG. 4 shows an SEM representation of mesoporous IrOx layers which have been calcined at different temperatures at the time before and after transfer from a glass-ceramic substrate to the polymer membrane. The mesopore morphology of the catalyst layer is also maintained at different temperatures.

[0137] FIG. 5 shows photographic and SEM images of catalyst layers on membranes. A catalyst-coated membrane produced by a preferred process according to the invention is compared with a catalyst-coated membrane from the prior art. The catalyst-coated membrane (i) having a mesoporous oxide layer prepared by the preferred process according to the invention has ordered mesopores and a nanocrystalline structure. In contrast, the catalyst-coated membrane (ii) produced from an ink by a spraying method does not have a defined nanostructure.

[0138] The diagram shown in FIG. 6 shows the electrocatalytic activity of a catalyst-coated membrane produced by the transfer method with a templateized mesoporous iridium oxide catalyst in comparison with a catalyst-coated membrane produced by a spray method with a commercial Ir catalyst. The membrane provided with a mesoporous catalyst layer via the transfer method achieves, with comparable geometric Ir loading, an Ir mass activity which is about 35% higher than that of the reference system. The same Pt/C catalyst which was applied via a spray process serves as cathode coating in both catalyst-coated membranes. The systems differ in the anode coatings.