Study of acetate adsorption at the platinum electrode/acid electrolyte interface using 'blocking effects': Influences of acetate adsorption on ethanol fuel cell electrodes

摘要

This manuscript describes results using a novel electrochemical approach that utilizes pulse sequences and surface blocking effects for the quantitative study of the accumulation of acetate ions and the influence of ethanol and molecular oxygen on those accumulations at a polycrystalline platinum electrode. The electrochemical properties of acetic acid are of special interest in connection with ethanol fuel cell technology where it is the main product of incomplete ethanol oxidation in laboratory fuel cells. Acetic acid adsorbs as the anion on a platinum electrode in an acid electrolyte. Adsorbed acetate ions block oxygen adsorption during an anodic potential scan, with a stoichiometry of two oxygen adsorption sites per adsorbed acetate ion. Use of this "blocking effect" has enabled the first-time determination of rates of acetate adsorption and desorption and of an adsorption isotherm normalized with respect to available surface sites. The ethanol adlayer is comprised of acetate and species other than acetate that block hydrogen adsorption during a cathodic scan while adsorbed acetate does not. Use of a combination of the "blocking effects" has enabled the first-time quantitative determination of the interaction between the two types of adsorbed species. Adsorbed acetate significantly impedes both ethanol oxidation and molecular oxygen reduction in fuel cells.