Excitability and multistability in the electrochemical oxidation of primary alcohols

Results are presented from experiments on the electrocatalyzed oxidation of I-butanol at a Pt electrode conducted under conditions of constant current in both acid and NaOH solutions. Several nonlinear behaviors are characterized. In acid solution, the oxidation of I-butanol exhibits excitability, i.e. a small perturbation induces a large amplitude excursion with mixed time scales before the system returns to stationary behavior. It is argued that excitability reveals that oxides directly partake in the oxidation process. Butanol oxidation also exhibits a tristable response in acid solution in which three different stationary states exist under the same conditions. A different tristability also occurs in which an oscillatory state coexists with two stationary states. Instead of a tristable response, the oxidation of 1-butanol displays a bistable response in NaOH solution. Results are compared with those obtained for alcohols with a smaller number of carbon atoms, ethanol and methanol. In view of results from potential controlled experiments, the results of the current controlled experiments reveal what can be considered nonintuitive current-potential relations. Relations among the observed nonlinear behaviors, current-potential relations, and mechanisms, as well as the differences between results obtained in NaOH solution and those obtained in acid solution are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.