The polarization curves of a single PEMFC having a Nafion membrane fed with H-2/O-2 with relative humidity (RH) of 35%, 70% and 100% were measured at cell temperatures ranging from 65 degrees C to 120 degrees C at back pressures of 0 atm and 1 atm, respectively. Measured results showed that the best cell performance at 0.6 V operated within 65-120 degrees C at zero back pressure was 1000 mA cm(-2) at 65 degrees C and RH = 100%, while the best cell performance at 1 atm back pressure was 1300 mA cm(-2) at 100 degrees C and RH = 100%. Based on the analysis of impedance data measured at anode and cathode humidification temperatures of 90 degrees C and cell temperature of 100 degrees C at back pressures of 0 and 1 atm (90-100p0 and 90-100p1), it could be found that the membrane resistance was reduced and the catalyst became more active as the back pressure increases. The present results showed that increasing back pressure was able to dramatically improve cell performance and the effect of the back pressure surpassed that of humidification in the internal resistance of cell. (C) 2011 Elsevier Ltd. All rights reserved.