An experimental investigation of the performance and contamination of low and high temperature PEMFCs (polymer electrolyte membrane fuel cells) operating with different concentrations of CO2 at the anode inlet is presented. 50 cm(2) MEAs are used in the investigation: Nafion membranes with catalyst Pt loading 0.5 mg cm(-2) for both anode and cathode for the low temperature cell, and Celtec P1000 PBI MEAs with catalyst loading 0.75 mg cm(-2) in anode and 1 mg cm(-2) in cathode for the high temperature cell. An analysis of the relative humidity influence in the contamination process for low temperature polymer electrolyte membrane fuel cells and the temperature effect for both low and high temperature operation range are also investigated in this work. The results show that the performance loss is larger than expected if only a dilution effect were considered, so that a real contamination process occurs in the cell when CO2 is fed to the anode, due to the RWGS (reverse water gas shift) reaction. This contamination effect is analysed and quantified by comparing the polarization curves of the contaminated cell with the ones corresponding to the cell operating with pure hydrogen, following the method described in section 2. The overpotentials for different current densities, CO2 concentrations, relative humidity, and cell temperatures are presented and discussed for both types of fuel cells. Two different regeneration processes (anode feeding with pure H-2 and with air) are also presented and discussed. The analysis of the effectiveness of each regeneration strategy also supports that CO produced via the RWGS reaction is adsorbed onto the catalyst. (C) 2015 Elsevier Ltd. All rights reserved.