While monolayer formation by under potential deposition of palladium from 0.1 M H₂SO₄ + 0.2 mM PdSO₄ onto Au(111) commences around 0.6 V vs. SCE (saturated calomel electrode), there is evidence for slow incorporation of Pd⁰ 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 [PdCl₄]²⁻, 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 H₂SO₄ + 0.2 mM PdSO₄ 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 H₂SO₄ is enormously high. The immersion time is crucial for the HER electrocatalytic activity.