Anion exchange membrane fuel cells operating near room temperature using hydroxide or carbonate as the conductive ions have been demonstrated and compared. A membrane electrode assembly was fabricated using a poly(arylene ether sulfone) polymer membrane functionalized with quaternary ammonium cations. The maximum power density using hydroxide as the conductive ion was 2.1 mW/cm(2). When CO2 was introduced to the cathode stream, the maximum power density increased to 4.1 mW/cm(2). CO2 was shown to be materially involved in the oxygen reduction reaction at room temperature and was transported from the cathode to the anode. CO2 was shown to be consumed at the cathode and evolved from the anode. The performance was analyzed by electrochemical impedance spectroscopy. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3058999] All rights reserved.