In-situ FT-IR spectroscopic study of bisulfate and sulfate adsorption on platinum electrodes. Part 1. Sulfuric acid

Abstract

The adsorption of bisulfate and sulfate ions on Pt in sulfuric acid has been studied by observing their asymmetric S-O stretching vibrations using potential difference Fourier transform infrared reflection absorption spectroscopy. It has been found that the two anions are coadsorbed over the potential range studied. A rather clear band of the bending mode of water was observed in the same spectra. This has been attributed to water molecules weakly bonded to the surface through H in the hydrogen region and O in the oxygen region. The band intensity ratio of sulfate against bisulfate ions is much larger than the calculated activity ratio in 0.5 M sulfuric acid solution, although the intensity ratio becomes closer to the calculated activity ratio in 0.05 M sulfuric acid. A large frequency shift with potential of 100 cm-1/V is observed for the adsorbed bisulfate ions in the double layer potential region, while the frequency shift is much smaller for sulfate ions. In the oxide formation region above 0.85 V (RHE), the sulfate ions appear to be replaced by bisulfate ions; this is interpreted as resulting from the formation of a hydrogen bond between HSO-4 and the negatively charged oxygen atoms which are present on the Pt surface. © 1989.