Pd deposition onto Au(111) electrodes from sulphuric acid solution

The initial stages of palladium deposition onto Au(111) from 0.1 M H2SO4 + 0.1 mM PdSO4 have been studied by cyclic voltammetry and in situ scanning tunnelling microscopy. While Pd is commonly deposited from chloride solutions, the effect of sulphate adsorption is considered in this work. A Pd monolayer is formed at underpotentials before a second monolayer grows at overpotentials. There is strong evidence that these two Pd layers are pseudomorphic with the Au(111) substrate. Sulphate is adsorbed on the pseudomorphic Pd layers over a wide potential range in a (3×7)R19.1° structure like in the case of massive Pd(111). The deposition process changes to three-dimensional growth with the third Pd layer, which has already bulk properties. This is indicated by the appearance of a voltammetric peak in the hydrogen adsorption region, which is characteristic for the behaviour of massive Pd(111). Differences to Pd deposition from chloride solutions are discussed.