ATR–SEIR study of anions and water adsorbed on platinum electrode

Adsorbed species on bare Pt, and UPD-Pb or UPD-Cu/Pt electrodes were characterized in HClO4 or H2SO4 solutions at various potentials using attenuated total reflection (ATR)–surface enhanced infrared absorption (SEIRA) spectroscopy. On the bare Pt electrode, ClO 4 - anions were observed at 1120–1095 cm−1 at +0.0 < E < +0.6 V, solvated by water molecules with OH stretching absorption at 3600 cm−1 and HOH bending mode at 1610–1620 cm−1. In addition to the S–OH totally symmetric mode at 950 cm−1, adsorbed sulfate species gave two bands at 1230–1100 cm−1 between 0.0 V < E < +0.8 V that are assigned to ν3 (symmetric stretch of S–O in SO3) of HSO 4 - ions with different coordination based on the peak shift by isotope substitution. At more negative potential, solely water molecules adsorb on the bare Pt surfaces. In contrast, it was found that electrolyte anions such as bisulfate and ClO 4 - with hydrating water molecules adsorb onto the UPD-Pb/Pt and UPD-Cu/Pt electrodes even at much negative potentials, e.g. −0.2 V for UPD-Pb.