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)/H2Q(aq)) redox couple at Bi-coated polycrystalline platinum (Ptpoly) electrodes. In 0.5 M HClO4 acid solutions, the observed rate of electron-transfer is controlled by the relative bismuth surface coverage present at the Ptpoly electrode surface. At full bismuth monolayer coverages, the reversibility of the Q(aq)/H2Q(aq) redox couple is considerably enhanced. Continued potentiodynamic cycling of the Q(aq)/H2Q(aq) couple at a Bi-coated Ptpoly electrode leads to a decrease in the Q(aq)/H2Q(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 Bi(aq)3+, no changes are observed during potentiodynamic cycling of the Q(aq)/H2Q(aq) redox couple and the reaction rates remain fast.