Deposition of catalytic electrodes of ion-exchange membranes

Abstract

A gas and electrolyte permeable metal layer is bonded to an ion-permeable membrane by electroless deposition to produce a permeable metal deposit upon the membrane or diaphragm. Advantageously, the membrane surface to be coated is pretreated with an amphoteric material. Thereafter, the treated surface is treated to deposit the coating. Typical metals deposited include platinum group metals, iron group metals, such as nickel, cobalt and others including gold and silver. The coatings are very thin, rarely in excess of about 50 to 100 microns. The coated membrane may be installed in an electrolytic cell used for producing chlorine and alkali by electrolysis of alkali metal chloride with the coating serving as one electrode and another opposed electrode on or adjacent to the opposite side of the membrane. It may also be used in water electrolysis and for other purposes. The coatings may be thickened by depositing other coatings of the same or different composition by suitable coating techniques. Especially adherent coatings are obtained when the metal deposited upon the pretreated surface is palladium metal or a mixture of palladium with another metal. Thickening coatings deposited upon such a porous palladium coating are found to have superior adherence and durability. The metal layer may be soaked or contacted with an alkali metal or an amalgam in presence of water to modify its crystal structure or grain size, if desired.