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

The initial stages of palladium deposition onto Au(111) from 0.1 M H 2SO 4 + 0.1 mM PdSO 4 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.