Polyoxometalate-deposited Pt/C electrocatalysts are prepared by impregnation with various amounts of polyoxometalate (POM) anions (from 2 to 16.7 wt.% PMo(12)O(40)(3-)) on the Pt/C catalyst. The prepared electrocatalysts show a high CO electrooxidation performance over a half-cell system for CO stripping voltammetry, and CO tolerant electrooxidation of H(2) is further demonstrated over a proton exchange membrane fuel cell by using CO-containing H2 gas feeds (0, 10, 50, and 100 ppm CO in H(2)). In the CO stripping voltammograms, the onset and peak potentials for the CO oxidation appear to decrease as the POM deposition is increased, indicating that the electrooxidation of CO undergoes more efficiently on the catalyst surface with the deposited POMs on the Pt/C catalysts. In the single fuel cell tests with the CO-containing H2 gases, the higher current density is also generated with the larger amounts of deposited POMs on the Pt/C catalysts. Importantly, the charge transfer resistance R(p) appears to decrease monotonically with the POM amounts, which was measured by electrochemical impedance spectroscopy. Physico-chemical characterizations with electrocatalytic analyses show that the deposited POMs hardly affect the active phase of Pt catalyst itself but can help the electrooxidation of H(2) by efficiently oxidizing CO to prevent the Pt catalyst from poisoning. Consequently, this POM-deposited Pt/c catalyst can serve as a promising CO tolerant anode catalyst for the polymer electrolyte fuel cells that are operated with hydrocarbons-reformed H(2) fuel gases. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.