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 w as studied with in situ FTIR spectroscopy in a HF/KF buffer solution o f pH = 2.8. This base electrolyte diminishes the effect of ion migrati on in the thin layer produced by the loss of solution ions upon adsorp tion. This allows a clear distinction between adsorbate and solution f eatures. 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 assi gned to adsorbed SO42-. Below 0.7 V, coadsorption of HSO4- 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 a t higher potentials. Lateral interactions increase with potential due to the increase in coverage.