In this work, formic acid oxidation on Pt nanoelectrodes modified by irreversible adsorption of Bi is presented. The coverage of Bi, as measured by voltammetry and X-ray photoelectron spectroscopy, was controlled from 0.05 to 0.25. Chronoamperometric measurement of the catalytic activities of the Bimodified Pt nanoelectrodes revealed that the catalytic enhancement depended on oxidation potential and Bi coverage: elemental Bi in the potential range from -0.1 V to 0.6V enhanced formic acid oxidation by factor of 4. while partially oxidized Bi in the potential range from 0.3 V to 0.7 V increased by factor of 8. The enhancement in the latter potential range was effective only when the Bi coverage was more than 0.18. Single cell performance of the Pt nanoelectrodes modified by Bi increased by factor of 2-3, depending on operation conditions such as formic acid concentration. temperature, and humidity in the feeding gas into cathode. When the Bi coverage was more than 0.18, the single cell performances were nearly identical. Based on measurement of adsorbed CO and catalytic poison from formic acid, an oxidation path not involving catalytic poison in the potential range from 0.5 V to 0.7 V is discussed in detail. (c) 2008 Elsevier Ltd. All rights reserved.