Composite membranes with hydrophilic substances can retain water and allow the operation of proton exchange membrane fuel cells (PEMFCs) under non-humidified conditions. In this work, thin Nafion composite membranes with silica are prepared to operate a PEMFC with dry fuel and oxidant. In addition, the role of silica in the catalyst layer as a water retainer is studied. In particular, the anode and the cathode are modified separately to elucidate the effect of silica. The incorporation of silica in the membrane and the catalyst layer enhances single-cell performance under non-humidified operation. The cell performance of membrane-electrode assemblies using the composite membrane and electrode is higher than that of a MEA using commercial Nafion 111 membrane under non-humidified conditions. (c) 2007 Elsevier B.V. All rights reserved.