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 character ized. In acid solution, the oxidation of I-butanol exhibits excitability, i .e. a small perturbation induces a large amplitude excursion with mixed tim e scales before the system returns to stationary behavior. It is argued tha t excitability reveals that oxides directly partake in the oxidation proces s. 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 com pared with those obtained for alcohols with a smaller number of carbon atom s, ethanol and methanol. In view of results from potential controlled exper iments, the results of the current controlled experiments reveal what can b e 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 th ose obtained in acid solution are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.