Abstract Palladium is shown to be deposited underpotentially on gold electrodes in 1 M H 2OSO 4. The deposit forms an alloy according to a t 1/2 law. The rate of alloy formation is strongly dependent on the potential. The diffusion coefficient is about 10 −16 cm 2 s −1. This value is discussed in comparison with earlier measurements on gold-palladium alloys at higher temperatures.