Electrochemical behaviour of aqueous SO2 at polycrystalline gold electrodes in acidic media: a voltammetric and in situ vibrational study Part 1. Reduction of SO2: deposition of monomeric and polymeric sulphur

The electro-reduction of SO2 has been monitored by using cyclic voltammetry , FT-IR spectroscopy and SER spectroscopy. Prior to the bulk reduction, SO2 is reduced to yield a monomeric sulphur adlayer at a maximum coverage of a bout 0.25. The sulphur adlayer undergoes a reversible redox surface process at E < 0.0 V (RHE), which implies a change in the frequency of the Au-S st retching mode from 270 to 300/310 cm(-1). In the potential region encompass ing the bulk reduction voltammetric peak, infrared spectra display a band a t 2585 cm(-1) attributable to a S-H vibration from a soluble species. Accor dingly, H2S or H2Sx were proposed as tentative bulk reduction products. In positive sweeps a broad anodic wave develops between 0.2 and 0.6 V that lea ves polymeric sulphur species adsorbed at multilayer level, with a S-S stre tching mode at 460 cm(-1) and a S-S-S bending vibration at 218 cm(-1). Mult ilayer sulphur can be removed reductively under a sharp cathodic peak. Acco rding to literature of the S(-II)/Au system, removal proceeds to yield solu ble S(-II) species, via intermediate polysulphides. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.