An investigation was made of the inward diffusion of underpotentially-deposited Cd into a Au(100) substrate in 50mol/m3 sulfuric acid solution under potential control. This involved anodic voltammetry at 295 to 333K, as well as electrochemical quartz crystal microbalance analysis and X-ray diffractometry. The anodic voltammograms showed that the inward diffusion of Cd adatoms into a Au(100) bulk phase could be classified into 2 types of step. One was a very fast step, which involved the diffusion of underpotentially-deposited Cd into a Au(100) electrode at the surface layer. The activation energy for this step was some 70kJ/mol. The other step was much slower, and its activation energy (110kJ/mol) agreed well with that for Cd bulk diffusion into a Au-Cd compound. The amount of underpotentially-deposited Cd was deduced from electrochemical quartz crystal microbalance analyses, and almost agreed with that obtained using anodic voltammetry. It was found that the amount of underpotentially-deposited Cd increased with temperature.

Temperature Dependence of Inward Diffusion of Underpotentially-Deposited Cd into a Au (100) Bulk Phase under Electrochemical Environment. T.Tanaka, K.Kubo, N.Hirai, S.Hara: Materials Transactions, 2003, 44[4], 688-91