FORMIC-ACID OXIDATION ON PT(111) ELECTRODES MODIFIED BY IRREVERSIBLY ADSORBED SELENIUM

The irreversible adsorption of selenium on Pt(111) electrodes allows P t(111) modified electrodes with a selenium coverage up to 0.5 to be pr epared and characterized voltammetrically. Such modified electrodes ha ve different electrocatalytic properties for formic acid oxidation tha n the unmodified Pt(111) electrode. Two different aspects of the formi c acid oxidation reaction were studied: (i) the catalytic enhancement of formic acid oxidation with selenium coverage and the influence of t he surface structure of the selenium adlayer and (ii) the inhibition o f the poison formation reaction from formic acid by the presence of ad sorbed selenium on the electrode surface. An increase in the catalytic activity of the modified electrode was found at selenium coverages gr eater than 0.20, maximum catalytic activity being achieved at a seleni um coverage of 0.28. With selenium coverages higher than 0.33, the cat alytic activity of the electrode diminishes. In the poison formation e xperiments, the poison formation reaction was inhibited by the seleniu m adatoms by a third-body mechanism. The complete inhibition of the po ison formation reaction occurred at a selenium coverage of 0.28, the c overage at which the maximum catalytic activity was found. A relations hip between the structure of the selenium adlayer and the catalytic en hancement is proposed.