DE4342859A1 - Cathode for hydrogen-generating cell contg. easily incorporated nickel catalyst - Google Patents

Abstract

Cathode for H2 generating cells, according to DE3532335 contains the reaction prod. (I) of thermal decomposition of the Ni salt (II) of an organic acid, pref. Ni formate (IIA) or oxalate as the Ni catalyst and esp. is used in conjunction with a Zn anode and alkaline electrolyte. The gas-generating electrode consists of activated charcoal (III) with PTFE as binder and contains Ni as catalyst; and the gas is discharged from the cell housing through a finely porous PTFE film. In the prodn. of the cathode, either (a) (III) powder is impregnated with aq. (II) soln., dried and heated above the decomposition temp. (Td) of (II) and the catalysed (III) powder is made into the electrode structure; or (b) the electrode structure is moulded from uncatalysed (III) powder, impregnated or sprayed with aq. (II) soln., dried and heated above Td.

Description

The invention relates to a cathode for use in water substance development cells according to DE-PE 35 32 335, which are preferred work with a zinc anode and alkaline electrolyte, whereby the gas development cathode made of PTFE-bonded activated carbon stands and contains nickel as a catalyst and the gas developed discharged from the cell housing via a fine-pored PTFE layer is, the nickel catalyst is the reaction product of ther mix disintegration of the nickel salt of an organic acid is preferably the nickel formate or the nickel oxalate. Against The invention also relates to processes for the production of these Electrodes.

How much the technology of hydrogen anodes and cathodes has developed from a variety of patents and knowledge scientific publications. So is the so-called Double skeleton catalyst electrode for hydrogen in the book E. Justi and A. Winsel, "Cold Combustion - Fuel Cells", Steiner-Verlag, Wiesbaden (1962). In EP-PS 144002 is a hydrophobic hydrogen electrode with Raney nickel as Catalyst and PTFE as a hydrophobic binder disclosed that is successfully used in hydrogen electrolysis. she is but also usable in the hydrogen development cell according to DE-PS 35 32 335. This latter patent discloses one galvanic cell, in an amount equivalent to the current Hydrogen is generated. In particular, the development of Hydrogen can be done without adding external energy if one a zinc electrode in combination with a hydrogen cathode used, both in a preferably alkaline electrolyte ten operated. By short-circuiting the cell via a con constant or variable resistance can be any Realize temporal hydrogen generation profiles. Because he generated amount of hydrogen is equivalent to electric current, can because of its extremely sensitive dosing the smallest amounts of liquid with the corresponding accuracy be changed. As a modification of one produced in large numbers The cell is also a product of the battery industry inexpensive. The metal / hydrogen cell according to DE-PS 35 32 335 be consists of the following parts:

• - From a housing with a cup part and a cover part, which are connected electrolytically by a plastic seal;
• - from a multilayer, biporous hydrogen electrode, which has a hydrophilic system of electrolyte-filled pores and a hy drophobic system of gas-filled pores and to the cup bottom arranged with a fine-pored hydrophobic layer made of PTFE which covers openings in the bottom of the cup;
• - Made of a porous or powdered metal electrode Cadmium or zinc, which is in the lid space and which over an ion exchange membrane and / or via a porous Separa is connected to the hydrogen electrode,
• - From an amount of electrolyte that the hydrophilic pores and Fills voids in the components.

It is also important that the cell voltage in the case of Zinc metal electrode 0.2 V to 0.6 V, in the case of Cadmium metal electrode is -0.2 V to 0.2 V.

It was found that the gas cell described is able to in the case of current passage in the opposite direction, the previously formed To bind hydrogen again and the zinc hydroxide formed like to reduce the zinc. This is not only possible with Ver Use of platinized or palladium-coated activated carbon in the Hydrogen electrode but also with Raney nickel as a catalyst gate. This known hydrogen catalyst requires a special dere technology of powder production, which in the beginning zi literature has been described, but based on the presence appropriate equipment is bound.

This gave rise to the task of creating a simpler procedure Electrode catalysis with nickel can be found with simple apparatus and carried out in the manufacturing process of Electrodes can be integrated. It turned out that the thermal decomposition of nickel formate or nickel oxalate Nickel metal catalyst with a very large surface area is created is characterized by low hydrogen overvoltage. Here two different methods have proven particularly useful:

• 1. This process is based on an activated carbon powder with large inner surface. The pore system of this activated carbon is with a concentrated, i.e. H. saturated, possibly warmed Solution impregnated with nickel formate. First, one finds Adsorption of the nickel formate on the coal surface instead.

After the impregnated activated carbon powder has dried, it becomes Powder to above the decomposition temperature of the formate increases. The very finely divided nickel catalyst separates on the inner surface of activated carbon, while hydrogen and form carbon oxides as decomposition gases. It is important that the oxidation of the nickel surface is as mild as possible in the air contact is made. That is why thermal decomposition is demonstrated partly with exclusion of air through. It turned out to be sufficient proven when 25 wt .-% of the finished catalyst powder Nickel exist; the rest is activated carbon.

The electrode structure is made from this catalyst powder by mixing it with 25 wt% PTFE powder in a mixer high-speed knives reactively mixed. The Kata lysator grains wound with the finest PTFE threads. It arises cotton-like material that forms a fur in a known manner rolled over. The fur is then rolled into a metal net and provides it with a thin, porous PTFE film. Out In this volume the small electrodes for the hydrogen are punched out winding cells.

• 2. It has now been shown that the order of the processes can reverse what is particularly for an economical manufacturing is advantageous. For this purpose you put out of nickel activated carbon as described in the previous paragraph the electrode tape. Then the tape comes with brought into contact with the aqueous nickel formate solution. First creates the impression as if the impregnation solution through the hy the hydrophobic effect of the PTFE would be repelled. With some ge duld notice, however, that the pores of the activated carbon soak up, a process that can be done by adding methanol, Accelerate isopropanol or other wetting agents can. If the pore system of the activated carbon is filled, then submit one the electrode tape of drying and decomposition for example by heating in a vacuum drying cabinet. Passes the impregnated The amount of catalyst is not sufficient, so you can use the impregnation process derholen.

The invention will be explained using two examples:

1. 10 g of nickel formate powder are distilled in 100 g Water entered. The solution is stirred until saturated, then decanted and heated to 60 ° C. In this solution  50 g of activated carbon are added with stirring. The activated carbon will filtered off, the filtrate dried and in a vacuum oven at 200 ° C. heated. The catalyzed activated carbon remains powdery without to make a cake. Now the coal with PTFE emulsion stirred and thickened to a pulpy consistency. This becomes rolled out a 0.5 mm thick layer on a polyethylene film, a nickel net was placed on top and rolled in tightly. After the dry The skin is provided with a porous PTFE film that Electrode discs are punched out and inserted into the cell vessels builds. The catalyst prepared according to the recipe above can but also with 20 wt .-% PTFE powder in a fast-running Knife mixer mixed and then dry to a fur be rolled. This skin is rolled into a Ni or Cu mesh and then provides it with a fine-pored PTFE film. Out Rounds punched out from this electrode band serve as cathodes in the hydrogen cells.

To 2. An uncatalyzed air electrode band is replaced by a ge saturated, 60 ° C warm nickel formate solution slowly moved through. After draining, the electrode tape is dried and opened 200 ° C heated. The electrode blanks are removed from this band punches and built into the cell vessels.

Claims (3)

1. Cathode for hydrogen development cells according to DE-PS 35 32 335, especially in connection with a zinc anode and with alkaline electrolyte, the gas development electrode consisting of PTFE-bonded activated carbon and containing nickel as a catalyst and the developed gas via a fine-pored PTFE layer released from the cell housing, characterized in that the nickel catalyst is the reaction product of the thermal decomposition of the nickel salt of an organic acid, preferably as the nickel formate or the nickel oxalate. 2. A method for producing the cathode according to claim 1, characterized by the following reaction steps

• - Preparation of an aqueous impregnation solution by dissolving nickel salts of organic acids
• - Impregnation of activated carbon powder with the impregnation solution
• - Drying and heating the impregnated activated carbon powder to above the decomposition temperature of the organic nickel salt.
• - Forming the electrode structure from the catalyzed activated carbon powder.

3. The method for producing the cathode according to claim 1, characterized by the following reaction steps

• - Forming the electrode structure from the uncatalyzed activated carbon powder.
• - Preparation of an aqueous impregnation solution by dissolving nickel salts of organic acids
• - Impregnation of the electrode structure by immersion in or spraying with the impregnation solution
• - Drying and heating of the impregnated electrode tape to above the decomposition temperature of the organic nickel salt.