An array of carefully selected commercial diffusion media (DM) in combination with different micro-porous layers (MPLs) were subjected to extensive performance testing over a wide range of operating conditions to delineate the effects of DM-MPL configuration on the cell performance. Along with in situ and ex situ AC impedance measurements, durability tests were also performed to isolate the corresponding ohmic and mass transfer characteristics under wet and dry conditions, and to probe the degradation in the internal structure of these sub-layers under short- and long-term operations. Results indicate the existence of a strong and complex interaction between the macro- and micro-porous layers of the gas diffusion electrode. However, the nature of this interaction does not follow any obvious trend with respect to the bulk properties of the tested DM materials, indicating that the multi-phase transport cannot be described solely through a capillary transport concept (i.e. pore size, porosity and hydrophobicity). in addition, the hydrophobic treatment of the DM is found to be beneficial to alleviate flooding under wet conditions, but this beneficial effect gradually diminishes as the operating conditions become drier. The presence of an MPL appears to mitigate the loss of hydrophobicity in the macro-porous DM under long-term operations. Finally, the interaction between the membrane and the DM is found to be considerably different on both electrodes, indicating that a half cell modeling approach considering only a single electrode would lead to less realistic predictions. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.