The performance of an ABPBI-based High Temperature H 2/O 2 PEMFC system was studied under different experimental conditions. Increasing the temperature from 130 to 170 °C improved the cell performance, even though further increase was not beneficial for the system. Humidification of the H 2 stream ameliorated this behaviour, even though operating above 170 °C is not advisable in terms of cell performance. A significant electrolyte dehydration seems to negatively affect the fuel cell performance, especially in the case of the anode. In the presence of 2% vol. CO in the H 2 stream, the temperature exerted a positive effect on the cell performance, reducing the strong adsorption of this poison on the platinum sites. Moreover, humidification of the H 2 + CO stream increased the maximum power densities of the cell, further alleviating the CO poisoning effects. Actual CO-O 2 fuel cell results confirmed the significant beneficial effect of the relative humidity on the kinetics of the CO oxidation process. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.