Applications of real-time infrared spectroscopy to electrocatalysis at bimetallic surfaces: I. Electrooxidation of formic acid and methanol on bismuth-modified Pt(111) and Pt(100)

Abstract

The influence of predosed bismuth upon the electro-oxidation of formic acid and methanol to CO 2 on Pt(111) and (100) in 0.1M HClO 4 is examined by means of voltammetry combined with real-time infrared spectroscopy. The substantial (up to 30–40-fold) enhancement of the formic acid electro-oxidation rates observed in the presence of bismuth on Pt(100) are observed to be due primarily to the attenuation in the degree of CO poison formation as discerned from FTIR. The adsorbed CO formation, which reaches near-saturation coverages in the absence of bismuth, is essentially eliminated for bismuth coverages above ca. 0.2. The production of terminal CO is triggered by the onset of formic acid oxidation, suggesting that it forms from a reactive intermediate rather than from formic acid itself. The bismuth-induced electrocatalysis of formic acid oxidation observed on Pt(111) apparently also arises in a similar manner, although the major poison in this case is not adsorbed CO. These electrocatalytic influences of bismuth are consistent with an “ensemble effect”, whereby poison formation is suppressed to a markedly greater degree than is the reactive precursor. In contrast, the electro-oxidation rates of methanol on Pt(100) and especially Pt(111) are diminished in the presence of predosed bismuth. In addition, the terminal CO coverages formed during methanol electro-oxidation correlate directly with the variation in the reaction rates by altering either the reactant concentration or the bismuth coverage. These results suggest that CO can act as a reaction intermediate for methanol electro-oxidation under these conditions. A consistency is observed in the degree of dissociation of formic acid and methanol to yield adsorbed CO on Pt(111) and Pt(100) in electrochemical versus UHV surface environments.