IN-SITU RADIOTRACER STUDIES OF SORPTION PROCESSES IN SOLUTIONS CONTAINING (BI)SULFITE IONS .1. POLYCRYSTALLINE GOLD

In this work, we report some new findings obtained by the in-situ radi otracer and voltammetric studies of the time, potential and pH depende nce of sorption processes on polycrystalline gold in ClO4- supporting electrolytes containing aqueous SO2. Besides this, adsorption behaviou r of species created from aqueous SO2 (HSO3-/SO32- ions and/or molecul ar SO2 as well as their oxidation and reduction products) is compared with that of HSO4-/SO42- ions in order to get a deeper insight into th e nature and sorption properties of oxidation products. Both the oxida tion and reduction of aqueous SO2 occur on a polycrystalline gold in a cid solutions between the onset of hydrogen and oxygen evolution. At h igher pH values (3.5 and 6.5) the onset of the oxidation processes shi fts towards more positive potentials and the electroreduction commence s at less positive potential values. It is probable that a poisoning e ffect owing to oxidized adspecies rather than the electrocatalytic beh aviour of adsorbed reduction products prevail over the electrooxidatio n phenomena. Both HSO4-/SO42- and S2O62- are presumably formed (and ad sorbed) on gold upon electrooxidation of aqueous SO2. The apparent inh ibition of the electrooxidation processes in acid solutions may most l ikely be due to the formation of some surface complexes consisting of oxidized adspecies and ''strongly bonded'' molecular SO2. Copyright (C ) 1997 Elsevier Science Ltd.