WO1996037003A1

WO1996037003A1 - Photoelectric catalyst application

Info

Publication number: WO1996037003A1
Application number: PCT/DE1996/000791
Authority: WO
Inventors: Peter Suchy; Roland Kircher; Christoph NÖLSCHER
Original assignee: Siemens Aktiengesellschaft
Priority date: 1995-05-19
Filing date: 1996-05-07
Publication date: 1996-11-21

Abstract

To apply a catalyst material to an electrode support, a photoconductive layer on an earthed electrically conductive substrate is negatively or positively charged; a correspondingly positively or negatively charged mixture of the catalyst material and a polymer material is applied electrostatically to the photoconductive layer; the photoconductive layer is exposed and discharged; the mixture of catalyst material and polymer material is electrostatically transferred to the correspondingly negatively or positively charged electrode support, and the mixture of catalyst material and polymer material is fixed on the electrode support by heat treatment.

Description

description

Photoelectric catalyst application

The invention relates to a method for applying catalyst material to an electrode carrier.

Fuel cells can play an important role for stationary and mobile energy generation. However, the production of fuel cells with a solid electrolyte, such as polymer electrolyte and solid oxide, or else with a liquid electrolyte, such as potassium hydroxide solution, phosphoric acid and molten carbonate, has hitherto been too expensive for widespread use (see: "Journal of Power Sources ", Vol. 37 (1992), pages 15 to 31). This applies to various individual processes, including the manufacture of electrodes, i.e. for catalyst application.

To date, the following methods have been used in particular to apply catalyst material to an electrode carrier: film casting (tape casting), screen printing (screen printing), sputtering, electrochemical deposition, brushing, rolling up and brushing on, and even more complex processes (see: EP 0 569 062 A2; Proceedings IFCC - The International Fuel Cell Conference, 1992, pages 353 to 356 and 357 to 360; Proceedings 28th IECEC - Intersociety Energy Conversion Engineering Conference, 1993, pages 1.1195 to 1.1201); in some cases, multi-layer structures are also realized ("Journal of Applied Electrochemistry", vol. 22 (1992), pages 1 to 7). However, these processes have not yet been brought to production maturity.

The object of the invention is to provide a method which permits inexpensive and mass-production-compatible catalyst application and can therefore be used in particular in fuel cells, but also in electrolysers, polymer batteries and supercapacitors. This is achieved according to the invention (variant A)

- That a photoconductive layer, which is located on an electrically conductive, grounded substrate, is negatively or positively charged;

- That a correspondingly positively or negatively charged mixture of the catalyst material and a polymer material is applied electrostatically to the photoconductive layer; - That the photoconductive layer is exposed and thereby discharged;

- That the mixture of catalyst material and polymer material is electrostatically transferred to the correspondingly negatively or positively charged or polarized electrode carrier;

and that the mixture of catalyst material and polymer material is fixed on the electrode carrier by a temperature treatment.

As an alternative, the procedure can also be followed (variant B),

- That a photoconductive layer, which is located on an electrically conductive, grounded substrate, is charged positively or negatively; - That the photoconductive layer is fully or partially exposed;

- That a correspondingly positively or negatively charged mixture of the catalyst material and a polymer material is applied electrostatically to the exposed areas of the photoconductive layer;

- That the mixture of catalyst material and polymer material is electrostatically transferred to the correspondingly negatively or positively charged or polarized electrode carrier; and that the mixture of catalyst material and polymer material is fixed on the electrode carrier by a temperature treatment. The method according to the invention also allows the catalyst material to be applied in the form of a pattern (structured coating), the edge region of the electrode carrier, for example, not being coated. In variant A, the photoconductive layer is first exposed at the points which are not to be coated with catalyst material, and then the mixture of catalyst material and polymer material is applied to the exposed points. In the case of variant B, the entire surface of the photoconductive layer is exposed in the case of an unstructured coating, and partial exposure in the case of a structured coating, ie only those locations which are to be coated are exposed.

In the method according to the invention, the exposure of the photoconductive layer, which is generally uniformly charged, is preferably carried out with a laser beam (very homogeneous exposure), but it can also be carried out with light. In this method, an electrolyte membrane (for fuel cells with solid electrolyte) or a current collector (for fuel cells with solid or liquid electrolyte) is advantageously used as the electrode carrier. In the case of fuel cells with liquid electrolyte, the electrode carrier can also be an electrolyte matrix. The mixture of catalyst material and polymer material is advantageously fixed on the electrode carrier by electromagnetic radiation or by hot pressing.

The catalyst material is preferably platinum or iridium or a platinum or iridium compound or alloy. However, other metals can also be used, such as palladium, ruthenium, gold, nickel and tungsten, and also metal compounds and alloys such as NiO and Laι_ _x Sr _x Mnθ3. The catalyst material can be used either directly as a powder or on a support material, such as carbon black or carbon powder. The catalyst material or the electrode Additives that are used in electrodes, such as NiO and ZrC> 2, can also be added to the material.

The polymer material can be a polymer electrolyte, such as poly (perfluoroalkylene) sulfonic acid and polyether ether ketone ketone (PEEKK), or a hydrophobic or hydrophilic material on the cathode or anode side, for example polytetrafluoroethylene for low-temperature fuel cells (polymer electrolyte and alkaline and phosphoric acid fumes). fabric cells), polymer batteries and supercapacitors. The binder materials usually used there can be used for high-temperature fuel cells. Preferably, in the process according to the invention, an ionic polymer (ionomer), i.e. a polymer which contains ionic groups as a constituent of the main chain or at the side thereof.

In the case of a structured coating, variant A is followed in detail, for example, as follows (see FIG. 1):

1. A photoconductive layer is evenly charged negatively. The photoconductive layer, which consists of inorganic substances such as selenium and arsenic compounds, or of non-toxic organic substances, is located on an electrically conductive, in particular on a metallic substrate, which is generally a metal drum, for example made of aluminum. Charging takes place in particular by corona discharge or spray or spray discharge. For this purpose, a negative is made on a tungsten wire running parallel to the metal drum

High voltage is applied, for example approx. -7000 V. The air surrounding the tungsten wire is thereby ionized and the photoconductive layer is negatively charged. A uniform distribution of the charge is achieved by means of a grid which is arranged between the tungsten wire and the metal drum, or by means of a brush. O 96/37003 1

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2. The photoconductive layer is exposed in a targeted manner, specifically at the points which should not be coated with catalyst material here - and later on the electrode carrier. The exposure is carried out in particular with a laser beam. Since the photoconductor becomes conductive at the exposed areas, the previously applied charge flows off via the grounded metal drum and an invisible image is created, which is characterized by the charge distribution. 3. To "develop the invisible image", a mixture of catalyst material and polymer material, ie the electrode material, is applied to the photoconductive layer. This is done in such a way that the electrode material is charged in the opposite manner to the metal drum, in the present case thus positively, for example to approximately +400 V. The electrode material is, for example, in a brush. If the metal drum is now guided past this brush, the electrode material - due to the potential difference (approx. 7400 V) - is electrostatically transferred to the charged, ie unexposed areas. The exposed areas remain omitted, since the potential difference of approx. 400 V is too small for a transmission of the electrode material in the selected geometrical arrangement. 4. After the electrode material has been applied to the photoconductive layer, the entire surface is exposed. This will discharge the photoconductor or metal drum. 5. The electrode material is electrostatically transferred to the electrode carrier. For this purpose, the electrode carrier is guided over the metal drum or the metal drum is rolled over the electrode carrier. At the same time, the electrode carrier is negatively charged or polarized in a manner corresponding to the charge of the electrode material. For this purpose, a negative high voltage is applied, for example, to a so-called transfer charger, which is, for example, a tungsten wire, on the side of the electrode carrier facing away from the metal drum approx. -5000 V. In this way there is a pattern-preserving transfer of the electrode material (to the electrode carrier).

6. The electrode material is preferably fixed on the electrode carrier by electromagnetic

Radiation, in particular by infrared or microwave radiation, i.e. by heat radiation on the front or back, or by hot pressing, for example between two rollers at a temperature of 120 to 280 ° C; this can also be done in several steps, as well as by combining heat radiation and hot pressing. Chemical or physical modifications can take place, for example by partial fusion of the polymer material with the electrode carrier and / or the catalyst material, by diffusion of the

Polymer material or the material of the electrode carrier, in particular above the softening points, and by polymerization processes in the case of material which was originally not completely polymerized. To optimize the morphological structure of the electrodes, for example the porosity, it can sometimes be advantageous if a component is present in the polymer material which volatilizes during the heat treatment. Such a component can advantageously also serve to largely encapsulate conductive components of the electrode material, i.e. to envelop, and in this way to facilitate the application to the electrode carrier.

7. The metal drum is finally cleaned, for example by means of a mechanical scraper. The remaining electrode material removed from the drum is collected and can be reused. The metal drum is subsequently completely discharged, for example by means of an extinguishing lamp. Here, the remaining charge flows off, so that a new coating process can be started. In the case of variant B, the procedure for a structured coating is, for example, as follows (see FIG. 2):

1. The photoconductive layer on the metal drum is charged uniformly positively (high voltage), for example to approximately +7000 V.

2. Those areas of the photoconductive layer which are to be coated are deliberately exposed. These locations correspond to the locations to be coated on the electrode carrier.

3. The electrode material, i.e. the mixture of catalyst material and polymer material is charged in the same way as the metal drum, in the present case thus positively, but to a lower value, for example to approx. +400 V. Therefore electrode material only reaches the exposed, i.e. discharged areas of the photoconductive layer, in the other areas there is a repulsive electric field. Discharge of the photoconductor or the metal drum is therefore not necessary.

4. In order to transfer the electrode material to the electrode carrier, the latter is negatively charged or polarized (high voltage), for example to approximately -5000 V, in a manner corresponding to the charge of the electrode material. In this way, a pattern-preserving transfer takes place.

5. The electrode material is fixed on the electrode carrier by means of heat radiation or hot pressing.

6. Finally, the metal drum is cleaned and completely unloaded.

The method according to the invention is also suitable for an endless roll coating. In addition, this process can be used to produce hydrophobic and / or hydrophilic structures. Furthermore, multi-layer electrodes can be produced, ie several layers are applied one above the other, and the electrode carrier is also coated on both sides possible, if necessary with different materials. The layers can differ in terms of geometry, structure and composition. For example, the first layer can be relatively coarse-grained and consist of polytetrafluoroethylene (PTFE), an ionomer and carbon and contain little or no platinum, while the second layer can contain a lot of platinum and no PTFE.

Claims

claims

1. Method for applying catalyst material to an electrode support, by the following steps: a photoconductive layer located on an electrically conductive, grounded substrate is charged negatively or positively; a correspondingly positively or negatively charged mixture of the catalyst material and a polymer material is applied electrostatically to the photoconductive layer; the photoconductive layer is exposed and discharged; the mixture of catalyst material and polymer material is electrostatically transferred to the correspondingly negatively or positively charged or polarized electrode carrier; the mixture of catalyst material and polymer material is fixed on the electrode carrier by a temperature treatment.

2. The method according to claim 1, characterized in that the photoconductive layer is exposed at locations which are not to be coated with the catalyst material, and that the mixture of catalyst material and polymer material is applied to the unexposed areas .

3. Method for applying catalyst material to an electrode carrier, characterized by the following steps: a photoconductive layer located on an electrically conductive, grounded substrate is charged positively or negatively; - The photoconductive layer is exposed completely or partially; a correspondingly positively or negatively charged mixture of the catalyst material and a polymer material is applied electrostatically to the exposed areas of the photoconductive layer; - The mixture of catalyst material and polymer material is electrostatically transferred to the correspondingly negatively or positively charged or polarized electrode carrier; the mixture of catalyst material and polymer material is fixed on the electrode carrier by a thermal treatment.

4. The method according to any one of claims 1 to 3, so that the photoconductive layer is exposed to a laser beam.

5. The method according to one or more of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that serves as an electrode carrier an electrolyte membrane or a current collector.

6. The method according to one or more of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t that metallic platinum or iridium or a corresponding metal compound or alloy is used as the catalyst material.

7. The method according to one or more of claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that an ionic polymer is used as the polymer material.

8. The method according to one or more of claims 1 to 7, characterized in that the mixture of catalyst material and polymer material is fixed by means of electromagnetic radiation or by hot pressing on the electrode carrier.

9. The method according to one or more of claims 1 to 8, d a d u r c h g e k e n n z e i c h n e t that the electrode carrier is coated on both sides.

10. The method according to one or more of claims 1 to 9, d a d u r c h g e k e n n z e i c h n e t that several layers are applied one above the other.

11. Electrode carrier with applied catalyst material, obtainable by the process according to one or more of the

Claims 1, 2 and 4 to 10.

12. Electrode carrier with applied catalyst material, obtainable by the method according to one or more of claims 3 to 10.