Verfahren zur Herstellung mehrschichtiger Gas-Diffusions-Elektroden

摘要

A porous gas diffusion electrode comprising two or more layers, each of which is formed of sintered metal powder, is produced by assembling together at least two coherent and pore-free layers which have been pre-formed by casting a suspension of a sinterable pulverulent material in a solution of a binding agent and evaporating the solvent, and subjecting the assembled layers to sintering whereby the metal particles in each layer are sintered together and the several layers are sintered into a unit, the binding agent being such as to form products which escape from the assembled layers on sintering to leave the layers in a porous state. The pre-formed layers may be produced by applying a suspension of powdered metal in a binder to a carrier, which may be of paper and decomposed during sintering or of a non-bonding material unaffected by sintering, e.g. iron or brass. The powdered metals used may be one or more of carbonyl Ni or Fe, electrolytic Cu, Ag, binary Raney allows of Al with Ni, Cu, Ag, Fe, Pd, or Mo, or similar alloys in which the removable metal is Zn or Mg, while the binders may be watersoluble animal glue, methyl cellulose, or "Zapon" varnish comprising nitrocellulose, hard gum and alkyd resin. In specific examples the materials used are carbonyl Ni, or sizes <5m in an acetone solution of Zapon varnish (material A) and a 1.6 mixture by weight of carbonyl Ni of size <5n and an alloy of equal parts by weight of Al and Ni of size 35-50m (material B). Three-layer electrodes may be made by preparing preforms of material A and placing between them a preform of material B in "Zapon" varnish binder followed by pressing and then sintering in hydrogen at 650 DEG C. whereafter the aluminium in the middle layer is removed with caustic soda solution. Alternatively the material B without binder may be placed between preforms produced by spraying paper or oxidized iron with material A. With iron carriers a stack of components for three electrode may be treated simultaneously. In another arrangement for a five-layer electrode, brass carrier discs are sprayed with material A, material B is sieved on to the coating and then sprayed with "Zapon" varnish and over a disc so coated, coatings uppermost, is placed a 2.1 mixture by weight of carbonyl Ni of size <5m and KCl of size 200-400m , which thereafter is covered by the coated face of another brass disc. After hot pressing and sintering, the potassium chloride is dissolved out.