Anodic dissolution of palladium in sulfuric acid: An electrochemical quartz crystal microbalance study

Regularities of formation of a palladium oxide layer and its cathodic reduction in 0.5 M H2SO4 at 0.5-1.3 V (SHE) are studied by cyclic voltammetry, x-ray photoelectron spectroscopy, and electrochemical quartz crystal microbalance. A pure Pd plate and a similar to0.5-mum-thick Pd coating on gold-sputtered quartz crystal is used for electrochemical and microgravimetric studies. It is shown that a Pd electrode dissolves electrochemically in 0.5 M H2SO4 when its potential is cycled between 0.5 and 1.3 V. In the case of similar to0.5-mum-thick Pd coating on the gold substrate, the decrease in the electrode weight during one anodic-cathodic cycle is 1.0- 1.5 mug/cm(2) . It is suggested that anodic process at 0.5-1.3 V (SHE) represents electrochemical oxidation of palladium, yielding a surface layer of poorly soluble Pd(OH)(2) and/or PdO phases, as expressed by the equation Pd + 2H(2)O reversible arrow (Pd(OH)(2)/PdO)(s) + 2H(+) + 2e. This surface layer, (Pd(OH)(2)/PdO)(s), undergoes reduction during the cathodic process. About 5% of the total amount of ionized palladium dissolve in electrolyte.