Abstract
Early stages of electroless nickel plating from an ammoniacal hypophosphite solution of pH 8.8 at 50°C with palladium‐activated Mo were investigated using TEM and SEM, potential measurements, and LSV. It was shown that activation of molybdenum in a 
solution resulted in the formation of palladium islands on the substrate. In the plating solution, the nickel deposition took place simultaneously, but it took place independently on the palladium islands and on the molybdenum substrate. It was concluded that the nickel deposition on the molybdenum substrate occurred upon a thin layer of nickel, electrolytically deposited during a spontaneous potential shift. The role of the palladium islands was to catalyze electrooxidation of hypophosphite and induce the potential shift. A potential arrest at −0.7V vs. SCE was observed on the palladium with a concomitant decrease in the oxidation rate of hypophosphite. This phenomenon was ascribed to competitive adsorption of hydrogen and possibly to poisoning of the palladium by a hydride 
. In systems of palladium with molybdenum and palladium with nickel, a synergistic effect of small amounts of one metal on the catalytic activity of the other was observed.