Review A review of gas diffusion layer in PEM fuel cells: Materials and designs Sehkyu Park 1 , Jong-Won Lee 2 , Branko N. Popov* Center for Electrochemical Engineering, Department of Chemical Engineering, University of South Carolina, 301 Main Street, Columbia, SC 29208, USA article info Article history: Received 6 September 2011 Received in revised form 21 December 2011 Accepted 28 December 2011 Available online 6 February 2012 Keywords: Gas diffusion layer Water management Proton exchange membrane fuel cell Macroporous substrate Microporous layer abstract The gas diffusion layer (GDL) plays a key role on reactant gas diffusion and water management in proton exchange membrane (PEM) fuel cells. This paper reviews recent developments of single- and dual-layer GDLs for PEM fuel cells and various materials and approaches used for development of novel GDL. A variety of carbon- and metal-based macroporous substrates are presented. Hydrophobic treatments using different fluori- nated polymers are addressed. Engineering parameters which control the performance of microporous layer such as carbon treatment, wettability, thickness, and microstructure are also reviewed. In addition, future prospects for development of new GDL development are discussed. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction The proton exchange membrane (PEM) fuel cell is becoming center of attention as an alternative power source for auto- motive and stationary applications, since it is capable of producing high power densities under rapid change in load [1,2]. However, effective water management is necessary in order to meet fast response to power required in a system, i.e., deficient water reduces ionic conductivity in the membrane and the catalyst layer (CL) as well as induces severe contact resistance between the membrane and the CL, whereas excessive water in the membrane-electrode-assembly (MEA) reduces catalytic sites for electrochemical reactions and impedes reactants transport through non-reactive region. Liquid water condensed from the water vapor and produced by oxygen reduction reaction at the cathode CL moves into the membrane or the gas diffusion layer (GDL). In the former case, higher liquid water pressure formed by electro-osmotic drag and electrochemical reaction at the interface between the membrane and the CL drives water flow toward the anode. In the latter, liquid water accumulates at the CL/GDL interface and then flows toward the gas flow channel when liquid water pressure exceeds a threshold pressure for water flow through the GDL determined by its pore geometry and hydrophobicity. The GDL in PEM fuel cells is sandwiched between the CL and the gas flow channel and its structure controls the * Corresponding author. Tel.: þ1 (803) 777 7314; fax: þ1 (803) 777 8265. E-mail address: popov@cec.sc.edu (B.N. Popov). 1 Present address: Pacific Northwest National Laboratory, Richland, WA 99352, USA. 2 Present address: Korea Institute of Energy Research, Daejeon 305-343, South Korea. Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 5850 e5865 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.12.148