New Results on the Adsorption of Sulfate Species at Polycrystalline Gold Electrodes. An in Situ FTIR Study

The adsorption of sulfate species at polycrystalline gold electrodes was studied with in situ FTIR spectroscopy in a HF/KF buffer solution of pH = 2.8. This base electrolyte diminishes the effect of ion migration in the thin layer produced by the loss of solution ions upon adsorption. This allows a clear distinction between adsorbate and solution features. Adsorption of sulfate starts at 0.4 V vs Pd/H 2, i.e. about 0.28 V positive to the reported potential of zero charge and reaches a maximum at 1.2 V. This result is in a good agreement with radiotracer data obtained in acid and neutral sulfate solutions. One band between 1165 and 1193 cm - 1 is observed at all studied potentials and is assigned to adsorbed SO 4 2 - . Below 0.7 V, coadsorption of HSO 4 - produces a very weak feature at 1100 cm - 1 . Below 1.0 V the adsorbate behaves as a lattice gas adlayer, but the ions seem to become more immobilized at higher potentials. Lateral interactions increase with potential due to the increase in coverage.