Proton exchange membranes for fuel cells that operate under hotter and drier conditions are of interest for improved heat rejection and to reduce poisoning by carbon monoxide in reformed hydrocarbon fuels. Polybenzimidazole/phosphoric acid membranes have good conductivity under hot. dry conditions but require use of very high amounts of platinum catalyst to overcome high over-potentials due to strong poisoning by phosphoric acid. Polybenzimidazole membranes made using bis-fluorinated acids were found to provide significantly better fuel cell performance at 100-110 degrees C under ambient pressure with 80 degrees C inlet dew point compared to membranes with phosphoric acid. Addition of simple metal oxides provided optimal conductivity. (C) 2007 Elsevier B.V. All rights reserved.