A catalyst that uses Rh deuteroporphyrin 2,4-disulfonic acid was demonstrated to catalyze electrochemical CO oxidation at low overpotentials. The catalytic activity was enhanced by the improvement of the adsorption method. The onset potential of the improved catalyst was less than 0.05 V (vs a reversible hydrogen electrode, at 60 degrees C). This onset potential is lower than that for other Rh porphyrin-based catalysts reported previously. The CO poisoning of a Pt electrode was mitigated by the addition of this Rh porphyrin complex into the electrolyte solution. The Pt anode of a proton exchange membrane fuel cell (PEMFC) is sensitive to CO. Electrochemical CO oxidation might be a key reaction to counteract CO poisoning. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3516636] All rights reserved.