Gas diffusion electrodes (GDEs) containing sulfonated polyether (SPE) ionomers as proton conducting binder have been prepared and evaluated in H-2/O-2 polymer electrolyte fuel cells. An autoclave treatment has been applied for the first time to a hydrocarbon ionomer for the preparation of GDEs. The GDEs worked well as anode without practical overpotential up to 800 mA/cm(2) of the current density. As cathode, the GDEs showed significant dependence on the SPE content and its ion exchange capacity (IEC). Higher catalyst utilization was achieved for the GDEs with higher SPE content due to enhanced proton conduction. Cyclic voltammetry implied higher catalyst utilization of the SPE-based GDEs than that of the conventional Nation (R)-based GDEs. Scanning transmission electron microscopy (STEM) revealed that the SPE ionomer coated uniformly on the surface of Pt/carbon black catalysts. Humidification conditions affect proton conductivity and swelling of the SPE ionomer and thus were crucial for the cathode performance. SPE ionomer with medium IEC (2.17 meq/g) served best in GDEs in terms of catalyst utilization. (c) 2007 Elsevier Ltd. All rights reserved.