無電解めっきにおける次亜りん酸ナトリウムのアノード酸化に対する金属の触媒活性

Abstract

The anodic oxidation of hypophosphite on nickel, palladium, platinum, gold and cobalt electrodes in sodium citrate solution was studied with special attention to the catalytic activity of the metals in electroless plating. The polarization curves exhibited the current peaks, that were probably attributable to the formation of anodic films on the electrode surface at noble potentials. The anodic currents of the ascending portion of the polarization curves increased with increases either the pH value or the concentration of hypophosphite. The reaction orders in regard to the concentrations of hyphosphite and hydroxyl ion were approximately 0.5 and 0.2 respectively, and were dependent to some extent on the type of metal electrode. The relative catalytic activity of the metals, evaluated by the potential values at an anodic current density of 1.0×10-4A/cm2, decreases in the order Au, Ni, Pd, Co and Pt. Anodic oxidation of hypophosphite did not occur on Cu and Ag electrodes. The apparent activation energies for the anodic reaction were 7.9, 11, 13, 21 and 14kcal/mol for Au, Ni, Pd, Co and Pt respectively. Thus, the activation energy of the metals in the anodic oxidation of hypophosphite increases in descending order of their catalytic activity.