Abstract

The electrooxidation in a pH 11 carbonate/hydrogen carbonate buffer electrolyte of benzyl alcohol (BA) and several primary and secondary aliphatic alcohols on polyNiTSPc- and Ni(OH)2-modified glassy-carbon (GC) and gold electrodes was studied by cyclic voltammetry (CV) and with an electrochemical quartz crystal microbalance (EQCM). The films were formed by repetitive cyclic voltammetry in Ni(II)tetrasulphophthalocyanine (NiTSPc) and nickel(II) nitrate solutions, respectively. Although previous XPS results indicated a very similar environment for the Ni(II) ion in polyNiTSPc and Ni(OH)2 electrodeposited films, their electrochemical behaviour is different, which is probably associated with the hydrophobic-hydrophilic character of the film. The aliphatic alcohols are oxidized on both polyNiTSPc/GC and Ni(OH)2/GC, whereas BA is oxidized only on the former. Probably the high hydration of Ni(OH)2 prevents the expulsion of water from the interface required for the oxidation of BA. On polyNiTSPc/Au/Q the oxidation of BA takes place exclusively, and with high efficiency, on the Au substrate. We attribute this lack of activity of Ni(III) in polyNiTSPc/Au/Q to the high activity of the gold substrate, which depletes the concentration of BA to such an extent as to preclude its reaction with Ni(III). The oxidation of primary and secondary aliphatic alcohols on polyNiTSPc/Au/Q also occurs at the gold surface only, although the current is higher in the presence of the film.