Incorporation of Pd into Au(111): enhanced electrocatalytic activity for the hydrogen evolution reaction.

While monolayer formation by under potential deposition of palladium from 0.1 M H(2)SO(4) + 0.2 mM PdSO(4) onto Au(111) commences around 0.6 V vs. SCE (saturated calomel electrode), there is evidence for slow incorporation of Pd(0) into Au(111) under the same experimental conditions at 0.8 V, already. The presence of chloride traces suppresses such incorporation by forming stable complexes like PdCl(4), which are strongly adsorbed on the surface. Less than 1% of a Pd monolayer are incorporated after immersion of Au(111) at 0.8 V into 0.1 M H(2)SO(4) + 0.2 mM PdSO(4) for 30 minutes. It is supposed that incorporated Pd preferentially occupies subsurface sites near Au steps, which is supported by theoretical calculations. Despite the low Pd coverage, the electrocatalytic activity for the hydrogen evolution reaction (HER) in 0.1 M H(2)SO(4) is enormously high. The immersion time is crucial for the HER electrocatalytic activity.