In this work the oxygen reduction reaction (ORR) electro catalytic activity of Fe2O3 and Mn2O3 nanopowders, and carbon black powder was compared and evaluated against that of a Pt-cathode in an air-cathode microbial fuel cell (MFC) using several electrochemical techniques. The total resistance of the cathode electrode determined by impedance spectroscopy was 9.6, 7.8, 7.6 and 21.6 Omega for Pt, Mn2O3, Fe2O3 and C, respectively. Although the Mn2O3 cathode had the lowest resistance, the highest power output in polarization tests was observed for Pt, followed by Mn2O3. Fe2O3 and C. The corresponding volumetric power outputs were 90, 32, 15 and 8 W m(-3). The ORR onset potentials determined using cyclic voltammetry have shown values of 783, 844, 696 and 562 mV vs Ag/AgCl for Pt, Mn2O3, Fe2O3 and C, respectively. Therefore, Mn2O3 exhibited the best ORR potential, whereas Pt exhibited the best volumetric power output. The MFCs based on these cathodes showed a performance decline with time, most likely due to the loss of the catalyst, catalyst deactivation, or parasitic reactions. The MFC based on carbon cathode showed the most stable behavior. In all tests, biofilms were, of course, formed at the various cathodes, but a microbially catalyzed ORR (biocathode) or a biofilm catalytically active for the ORR was not observed. The Mn2O3 electrode appeared to be the most promising non-noble electro catalyst cathode; however its high overpotential (activation loss) should be improved in order to increase significantly the power generation. (C) 2011 Elsevier Ltd. All rights reserved.