抄録
Amorphous Co-P alloys have been deposited by d.c. and pulse plating from Watts-type Co plating bath containing phosphorous acid, and their electrochemical properties in sulfuric acid solution have been studied by means of electrochemical polarization and impedance measurements. Pulse conditions were found to have profound effects on the nature of the deposits. In particular, the Co-P alloys pulse-plated at low duty cycles, namely electrodeposited at high activation overpotentials, exhibited an amorphous alloy phase having a high degree of homogeneity, in spite of their very low phosphorus content less than 4.0 mass%P compared with those of d.c.-plated Co-P alloys. The amorphous Co-P alloys exhibited high corrosion resistance in contrast with pure Co deposit. This may be attributable to the formation of a uniform protective film containing phosphates. The electrocatalytic activity of the amorphous Co-P alloys for cathodic hydrogen evolution was one order of magnitude higher than that of pure Co, although the exchange current density was considerably low. This high activity for hydrogen evolution can be ascribed to the low Tafel slope, which is originated from the reaction mechanism. The amorphous Co-P alloys, having high corrosion resistance and high electrocatalytic activity for hydrogen electrode reaction, can possibly be used as cathode material for water electrolysis.
