Anion-exchange membranes (AEMs) with varying amounts of quaternary ammonium groups (0.51, 0.70, and 0.90 mmol g(-1)) grafted onto a styrene-ethylene/butylene-styrene (SEBS) block copolymer were prepared and studied for their impact on the performance of solid electrolyte H-2/O-2 fuel cells. A higher content of quaternary ammonium groups in the membranes resulted in higher ionic conductivity and lower OH- transport activation energy in the membranes, which in turn resulted in lower cell overpotentials and higher power density in the performance of the AEM fuel cells. By increasing the quaternary ammonium group from 0.51 to 0.90 mmol g(-1) in the AEMs, the power density of the AEM fuel cells at 50 degrees C was found to increase from 169 to 285 mW cm(-2). For comparison, the performance of AEM fuel cells using a commercial Tokuyamma A901 AEM was also tested. Electrochemical impedance spectra (EIS) recorded during the operation of the AEM fuel cells revealed that the transportation resistance of the OH- ions from the cathode to the anode through the AEM depended on the nature of the AEM and the cell voltage and is a critical factor to consider for improving the performance of AEM fuel cells. (C) 2012 Elsevier B.V. All rights reserved.