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-prop anol and 1-butanol at a rotating Pt disk in alkaline solution reveals qualitatively different responses among the alcohols. At low concentra tions, cyclic voltammograms (CVs) for each alcohol display a peak in t he Pt oxide region. Only 1-butanol CVs display this peak at high conce ntrations. 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 pote ntial cycles to retrace itself, a period-two CV. The period-two CV ari ses 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 c ycle of the period-two CV. During the other cycle, most of the PtOH re acts with an intermediate of the oxidation process. Other high-order p eriodic CVs appear at points of instability for ethanol but not for 1- propanol. It is concluded that the domain in constraint space for inst abilities decreases with increasing length of the carbon backbone.