Effect of bismuth surface coverage on the kinetics of quinone-hydroquinone at polycrystalline platinum electrodes

Auger electron spectroscopy (AES), linear sweep voltammetry and coulometry have been used to investigate the effect of bismuth surface coverage over the electron-transfer kinetics of the quinone/hydroquinone (Q((aq))/H(2)Q((aq)) redox couple at Bi-coated polycrystalline platinum (Pt-poly) electrodes. In 0.5 M HC1O(4) acid solutions, the observed rate of electron-transfer is controlled by the relative bismuth surface coverage present at the Pt-poly electrode surface. At full bismuth monolayer coverages, the reversibility of the Q((aq))/H(2)Q((aq)) redox couple is considerably enhanced. Continued potentiodynamic cycling of the Q((aq)/)/H(2)Q((aq)) couple at a Bi-coated Ptp.ly electrode leads to a decrease in the Q((aq))/H(2)Q((aq)) redox rates. The decrease in redox rates is accompanied by the simultaneous decrease in Bi-(ad) surface coverage and a concomitant increase in the chemisorption of hydroquinone-derived adspecies. Eventually, all Bi-(ad) is displaced and electron-transfer takes place slowly, through a spontaneously adsorbed hydroquinone-derived adlayer. In sharp contrast, in the presence of 1 mM B (aq), no changes are observed during potentiodynamic cycling of the Q((aq))/H(2)Q((aq)) redox couple and the reaction rates remain fast. (C) 2007 Elsevier B.V. All rights reserved.