Micro-porous layers (MPLs) prepared with different carbon materials were investigated. By the analysis of morphology, wettability and pore structure, the characteristics of each gas diffusion layer (GDL) were compared. A high efficiency bi-functional MPL with composite carbon black consisting of 20 wt.% Black Pearls 2000 carbon and 80 wt.% Acetylene Black carbon is proposed to enhance the transportation of both reactant gases and liquid water. Furthermore, a novel GDL with a gradient in porosity formed by adding MPLs with different carbon loadings on the catalyst layer side and on the flow field side is suggested for improved liquid water removal. (c) 2006 Elsevier B.V. All rights reserved.