New insight into the anomalous codeposition of alloys

SUMMARYA new modelfor the anomalous codeposition of alloys is based on the kinetic characteristics of metal electrodeposition and the effect of hydrogen evolution accompanying the deposition. The less noble metal has intrinsically faster kinetics and so its deposition rate can be controlled mainly by diffusion mass transfer in a certain range of overpotentials; the convection induced by hydrogen evolution can speed up the relative deposition rate of this less noble metal when it is mainly diffusion-influenced. In contrast with previous models, such as the hydroxide suppression hypothesis, the monohydroxide-discharge-controlled mechanism, and the competitive adsorption effect, our model can explain naturally and completely anomalous codeposition, i.e. the preferential deposition of the less-noble metal, a problem in alloy electrodeposition that has persisted for a century.