Electrochemical Ni-Mo alloying of the surface of a nickel substrate was investigated using alternating pulsed electrolysis in an aqueous solution containing only molybdate ions (MoO42-) as a metal ion component. In this electrochemical process, the nickel substrate was slightly dissolved during the anodic pulses, providing nickel ions into the solution in the vicinity of the substrate, while Ni and Mo were both electrodeposited on the substrate surface during the subsequent cathodic pulses. Through the optimization of anodic and cathodic conditions independently based on a set of direct-current electrolysis data, amorphous Ni-Mo alloy layers were found to be formed at the surface of the nickel substrate by the alternating pulsed electrolysis using the MoO42- solution of pH 3.0-5.0. The conditions for Ni-Mo alloy formation were discussed in terms of the dissolving regime of ionic species in the electrolytes determined by an equilibrium calculation. (C) 2007 Elsevier Ltd. All rights reserved.