PREPARATION AND PROPERTIES OF RANEY-NICKEL ELECTRODES ON NI-ZN BASE FOR H-2 AND O-2 EVOLUTION FROM ALKALINE-SOLUTIONS .1. ELECTRODEPOSITION OF NI-ZN ALLOYS FROM CHLORIDE SOLUTIONS

Experimental results for the electrodeposition of Ni-Zn alloys from chloride solutions, with addition of H3BO3 and without other additives, in a laboratory cell with a perforated nickel sheet cathode and with recirculating electrolyte are presented. The dependence of the zinc content in the alloy on the following operating conditions was investigated: cathodic current density, 1.0-20.0 A dm-2; temperature, 35-65-degrees-C; pH 1.5-5.5; total molarity, M(tot) = M(Ni)2+ + M(Zn)2+ = 1.1 - 2.8 M; and, molar ratio, P = M(Ni)2+/M(Zn)2+ = 1.0 - 15. Depending on the operating conditions the Zn content in the alloy varied over the range 22-88 mol %. In separate experiments galvanostatic polarization curves were measured in the direction of increasing and then decreasing cathodic current density in the range 0.1-20.0 A dm-2 with all other operating conditions as used for electroplating experiments. In all cases significant hysteresis effects were observed. It was found that the current efficiency for the electrodeposition of Ni-Zn alloys from chloride solutions as a function of the zinc content in the alloy showed a sharp minimum of about 55 % at X(Zn) = 55 mol % irrespective of other operating conditions.