Journal of Power Sources 190 (2009) 110–120 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Characterization of water transport in gas diffusion media Christian Quick a,∗ , Dietrich Ritzinger a , Werner Lehnert b , Christoph Hartnig b a Freudenberg Fuel Cell Component Technology KG, D-69465 Weinheim, Germany b Centre for Solar Energy and Hydrogen Research, D-89081 Ulm, Germany article info Article history: Received 3 June 2008 Received in revised form 28 July 2008 Accepted 31 July 2008 Available online 19 August 2008 Keywords: PEM fuel cell Gas diffusion layer Water management Water transport abstract An in-depth insight in the role of gas diffusion layers (GDLs) and its impact on the water management is a key issue for the optimization of fuel cells. A new ex situ test method is developed to investigate the water transport in gas diffusion media for polymer electrolyte membrane fuel cells (PEMFCs). This research is focused on properties of GDLs, which influence the water removal and water retention in the cell. Gas diffusion media are evaluated ex situ in terms of liquid water and water vapor transport employing a conventional PEMFC setup. The amount of water transported through a GDL and out of the cell is deter- mined by the properties of the gas diffusion medium. GDL properties such as the GDL thickness have a significant impact on water transport behavior. Furthermore, high impregnation weight or an additional micro-porous layer (MPL) reduces water removal due to enhanced mass transport resistances. The com- position and distribution of the impregnation material in the GDL substrate also play a crucial role. Water transport rates depend not only on the GDL properties but increase exponentially with cell temperature. Finally, a two-phase water transport model is proposed taking into account both diffusive gas phase and liquid water transport in diffusion media. Based on this model, ex situ data set in correlation with in situ performance in PEMFCs on dry operating conditions and guidelines towards new design concepts for gas diffusion media are deduced. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Water management plays an important role for a high per- formance and efficient operation of PEMFCs [1–3]. On the one hand, the polymer electrolyte membrane has to be hydrated suffi- ciently to ensure a good proton conductivity, which increases with increased water content [4]. Water is produced at the cathodic cat- alyst layer (CL) in the electrochemical reaction. Additionally, the reactant gases can be humidified. On the other hand, the active sur- face of the CL as well as pores in the GDL can be flooded by excessive liquid water, resulting in a higher mass transport resistance [5–7]. The consequence is oxygen transport limitation at the active layer that finally lowers fuel cell performance. Regarding this conflict- ing role of water, a delicate balance is required. So far, no generally applicable strategy for optimal water management in PEMFCs is available because water transport in the different components of a Abbreviations: atm, atmosphere (ambient pressure); CB, carbon black; CCM, catalyst-coated membrane; CL, catalyst layer; FEP, fluorinated ethylene propylene copolymer; GDL, gas diffusion layer; ip, in-plane direction; MEA, membrane elec- trode assembly; MPL, micro-porous layer; PEMFC, polymer electrolyte membrane fuel cell; PTFE, polytetrafluoroethylene; tp, through-plane direction; wt, weight. ∗ Corresponding author. Tel.: +49 6201 80 2289; fax: +49 6201 88 2289. E-mail address: christian.quick@freudenberg.de (C. Quick). fuel cell is influenced by operating conditions like humidification level of the reactant stream, reactant stoichiometric ratio as well as the temperature and pressure of the cell. Furthermore the geomet- ric characteristics of the flow field and the physical characteristics of the membrane and the GDL have a strong impact on the water transport [8]. Among the PEMFC components, the GDL plays a crucial role for a high performance because the diffusion media has lots of impor- tant tasks in the fuel cell. On the one hand the reactant gases have to be distributed homogeneously from the flow field to the CL for the electrochemical reaction. On the other hand the GDL should remove heat and excess water from the electrode to prevent local hotspots and catalyst flooding. Further the diffusion medium rep- resents a mechanical reinforcement for the mechanically sensitive catalyst-coated membrane (CCM) [9,10]. The required properties of a GDL are therefore good electrical and thermal conductivity as well as high thermal and chemical resistance and enhanced water and gas permeability. However, some of these requirements are contradictive. For example, air and water permeability increase with higher porosity, contrary to mechanical properties, electrical and thermal conductivity. Additionally all these mentioned charac- teristics are influenced by the GDL thickness, hydrophobicity and alignment of the carbon fibers. For further information Mathias et al. gave a comprehensive overview of GDL structure and functions [9]. 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.07.093