MECHANISTIC EXPLANATION FOR A SUBHARMONIC BIFURCATION AND VARIATIONS IN BEHAVIOR IN THE VOLTAMMETRIC OXIDATIONS OF ETHANOL, 1-PROPANOL AND 1-BUTANOL

Application of cyclic voltammetry to the oxidations of ethanol, 1-propanol and 1-butanol at a rotating Pt disk in alkaline solution reveals qualitatively different responses among the alcohols. At low concentrations, cyclic voltammograms (CVs) for each alcohol display a peak in the Pt oxide region. Only 1-butanol CVs display this peak at high concentrations. Increasing the alcohol concentration causes an instability for ethanol and 1-propanol. Beyond the instability a different stable response ensues in which the current-potential curve requires two potential cycles to retrace itself, a period-two CV. The period-two CV arises because of the dual role of the surface species that we call PtOH. A substantial amount of PtOH is transformed to Pt oxides during one cycle of the period-two CV. During the other cycle, most of the PtOH reacts with an intermediate of the oxidation process. Other high-order periodic CVs appear at points of instability for ethanol but not for 1-propanol. It is concluded that the domain in constraint space for instabilities decreases with increasing length of the carbon backbone.