APPLICATIONS OF REAL-TIME INFRARED-SPECTROSCOPY TO ELECTROCATALYSIS AT BIMETALLIC SURFACES .1. ELECTROOXIDATION OF FORMIC-ACID AND METHANOLON BISMUTH-MODIFIED PT(111) AND PT(100)

The influence of predosed bismuth upon the electro-oxidation of formic acid and methanol to CO2 on Pt(111) and (100) in 0.1M HClO4 is examin ed by means of voltammetry combined with real-time infrared spectrosco py. 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 absorbed CO formation, which reaches near-saturation coverages in the absence of bismuth, is essentially eliminated for bismuth coverages above ca. 0.2. The produ ction of terminal CO is triggered by the onset of formic acid oxidatio n, suggesting that it forms from a reactive intermediate rather than f rom formic acid itself. The bismuth-induced electrocatalysis of formic acid oxidation observed on Pt(111) apparently also arises in a simila r manner, although the major poison in this case is not adsorbed CO. T hese electrocatalytic influences of bismuth are consistent with an "en semble effect", whereby poison formation is suppressed to a markedly g reater degree than is the reactive precursor. In contrast, the electro -oxidation rates of methanol on Pt(100) and especially Pt(111) are dim inished in the presence of predosed bismuth. In addition, the terminal CO coverages formed during methanol electro-oxidation correlate direc tly with the variation in the reaction rates by altering either the re actant concentration or the bismuth coverage. These results suggest th at CO can act as a reaction intermediate for methanol electro-oxidatio n under these conditions. A consistency is observed in the degree of d issociation of formic acid and methanol to yield adsorbed CO on Pt(111 ) and Pt(100) in electrochemical versus UHV surface environments.