Effects of carbon black in micro-porous layer (MPL) on the performance of H-2/air proton exchange membrane fuel cells (PEMFCs) were studied and characterized extensively. Physical properties of gas diffusion layers (GDLs) involving surface morphology, gas permeability, hydrophilic/hydrophobic porosity and electron conductivity were examined. To construct an effective bi-functional pore structure, a novel MPL using composite carbon black consisting of Acetylene Black and Black Pearls 2000 carbon was presented for the first time. An optimal cell performance with the maximum power density of 0.91 W cm(-2) was obtained by the MPL containing 10 wt.% Black Pearls 2000 in composite carbon black. (c) 2006 Elsevier Ltd. All rights reserved.