In situ radiotracer and voltammetric study of the formation of surface adlayers in the course of Cr(VI) reduction on polycrystalline and (111) oriented platinum

This paper is focused on the in situ radiotracer and voltammetric studies of the induced HSO4-/SO42- adsorption at Pt(poly) and Pt(I 11) surfaces in 0.1 mol dm(-3) HClO4 solution in the course of Cr(VI) electroreduction. Besides this, the sorption behavior of HSO4-/SO42- ions on bare Pt(poly) and Pt(111) electrodes is compared and discussed. From the experimental results it can be stated that: (i) although the extent of bisulfate/sulfate adsorption is strongly dependent upon the crystallographic orientation of Pt surfaces, the maximum coverage on the Pt(I 1 1) does not exceed 0.2 monolayer; (ii) the Cr(VI) electroreduction on both poly- and (I 11) oriented platinum proceeds via a cc (chemical-electron-transfer) mechanism to yield Pt surfaces covered with intermediate surface adlayers containing Cr(VI) particles (and reduced Cr-containing adspecies) and I strongly bonded' HSO4-/SO42- ions; (iii) while the coverage of platinum surfaces by the intermediate complexes formed in the course of Cr(VI) electroreduction at E > 0.20 V is basically independent of the crystallographic orientation of the Pt electrode, the onset for rapid Cr(VI) reduction is highly affected by the nature and crystallographic orientation of the electrode. (c) 2006 Elsevier Ltd. All rights reserved.