Electricity production from carbon monoxide (CO) in a microbial fuel cell (MFC) has recently been demonstrated. Efficient operation of this MFC requires a CO-tolerant and preferably inexpensive cathode. Pyrolised CoTMPP, FeTMPP, and Co/FeTMPP gas diffusion cathodes were tested in MFCs operated on acetate or CO. When the MFC was fed with acetate the best cathode performance was obtained when using a Co/FeTMPP (3:1) cathode with a Me catalyst load of 0.5 mg cm(-2), although this performance was slightly lower than that obtained with a cathode containing 0.5 mg-Pt cm(-2). Tests using a MFC operated on CO showed a higher power output when using the Co/FeTMPP cathode when compared both with CoTMPP and Pt cathodes. Crown Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.