Influence of CO2 dissolution into anion exchange membranes (AEMs) on fuel cell performance was investigated. The conductivity of AEM decreased with an increase in carbonate ion species. For the power generation test with a supply of humidified H-2/O-2, the IR-free cell potential difference for the membrane electrode assembly (MEA) with the HCO3- form membrane was lower than that with the OH-form membrane. This low cell potential difference became noticeable by the supply of CO2 to either anode or cathode. The increment of ohmic resistance was confirmed by the supply of CO2 to cathode, but no obvious change in ohmic resistance was observed by the supply of CO2 to anode. Then, a CO2 permeation flux was determined by a gas chromatograph analysis of exhaust gas, and the correlation between the AEM fuel cell performance and the composition of ion species in the membrane was discussed. (C) 2012 Elsevier Ltd. All rights reserved.