In the present work, we report some new findings obtained by in-situ radiotracer and voltammetric studies of HSO3-/HSO32- (or/and molecular SO2) and HSO4-/SO42- sorption on polycrystalline gold in ClO4- supporting electrolytes in the pH range 0-6.5. The following conclusions can be drawn from the results presented in this paper(i) Both the oxidation and reduction of aqueous SO2 (bisulfite/sulfite ions or/and molecular 802) occur on a polycrystalline gold electrode in 1 mol dm-3 HClO4 between the onset of hydrogen and oxygen evolution. At higher pH values (3.5 and 6.5) the oxidation processes appear at more positive potentials and the electroreduction commences at less positive potential values. No reduction of bisulfite/sulfite proceeds above E = 0.00 V in 1 mol dm-3 NaClO4 (pH=6.5) solutions. (ii) The rate of the bisulfite/sulfite oxidation on gold is primarily affected by the accumulation of both reduction and oxidation products. It is probable that a poisoning effect owing to oxidized adspecies rather than the electrocatalytic behaviour of adsorbed reduction products prevail over the electrooxidation phenomena. (iii) The potential dependent accumulation of species created from aqueous SO2 can solely be detected on oxide-free gold surfaces. The extent and kinetics of sorption phenomena are highly influenced by the solution pH, the polarization potential and the "activity" (pretreatment) of the gold surface. (iv) The reduction of bisulfite (or/and molecular SO2) on gold in 1 mol dm-3 HClO4 most likely proceeds via elemental sulfur to yield surface sulfides at potentials E ≤ 0.05 V. (v) The adsorption strength of bisulfate/sulfate ions is substantially lower than that of adspecies formed from aqueous SO2 (bisulfite/sulfite ions, molecular SO2 as well as their oxidation and redaction products). (vi) From comparative studies of bisulfite/sulfite and bisulfate/sulfate accumulations on gold, it appears to be plausible that both bisulfate/sulfate and dithionate are formed (and adsorbed) on gold upon electrooxidation of aqueous SO2. The apparent inhibition of the electrooxidation processes in acid solutions may probably be due to the formation of some surface complexes consisting of oxidized adspecies and "strongly bonded" molecular SO2.
|Number of pages||13|
|Journal||Magyar Kemiai Folyoirat, Kemiai Kozlemenyek|
|Publication status||Published - Jun 1 1997|
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