Comparative study of the adsorption of SO42–/HSO4– and Cl– anions on smooth and rough surfaces of noble metal electrodes by in-situ radiotracer thin gap method

摘要

The so-called in-situ thin gap method for the measurement of the surface excess of the radiolabelled species was originally designed for the application of noble metal electrodes with low surface roughness. Therefore, the observation of adsorbed species containing radioisotopes of high specific activity (i.e., 35S and 14C) was only possible. A recent extension of the original thin gap method to metals with a surface roughness factor higher than 10, however, made it possible to follow the adsorption of species with low specific activity (i.e., 36Cl). Based on the validation of the improved thin gap method [Horváth et al, Electrochim. Acta 109 (2013) 468], this study aims at the comparison of the sulfate/bisulfate and chloride adsorption on both smooth (Pt and Au) and rough (platinized platinum) noble metal electrodes. It was found that the radiation signal of the adsorbed chloride ions can also be detected, and the surface excess of both radiolabelled bisulfate and chloride ions can be measured. The accumulation of the adsorbed species on rough electrodes took place at a much longer time scale than the removal of the same species. No such difference was found for smooth electrodes. The apparent asymmetry in the temporal behaviour of the adsorption and desorption processes on rough electrodes could be understood by the difference in the concentration gradient in the solution near or within the porous structures during the respective processes.