We report the synthesis and electrochemical characterization of rhodium/carbon (Rh/C) and palladium-rhodium/carbon (Pd-Rh/C) nanocatalysts for ethanol oxidation. Our results, for the first time. demonstrated that in an alkaline environment. Rh/C shows a much higher catalytic activity at low potential range than that of Pd-Rh/C and Pd/C. Intermediate species are produced during the oxidation process on Rh/C, as revealed by the complex impedance spectra (e.g., pseudo-inductive loop) at low potential range (i.e., -0.5 to -0.3 V). Adsorbed oxygen species, which are generated at high potentials, block active surface sires of Rh/C, resulting in the negative polarization resistance. (C) 2011 Elsevier B.V. All rights reserved.