International Journal of Hydrogen Energy 32 (2007) 4489 – 4502 www.elsevier.com/locate/ijhydene Effects of flow field and diffusion layer properties on water accumulation in a PEM fuel cell J.P. Owejan a , ∗ , T.A. Trabold a , D.L. Jacobson b , M. Arif b , S.G. Kandlikar c a General Motors Fuel Cell Activities, 10 Carriage Street, Honeoye Falls, NY 144720603, USA b National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, MD 208998461, USA c Department of Mechanical Engineering, Rochester Institute of Technology, 76 Lomb Memorial Drive, Rochester, NY 14623, USA Received 4 April 2007; received in revised form 31 May 2007; accepted 31 May 2007 Available online 7 September 2007 Abstract Water is the main product of the electrochemical reaction in a proton exchange membrane (PEM) fuel cell. Where the water is produced over the active area of the cell and how it accumulates within the flow fields and gas diffusion layers, strongly affects the performance of the device and influences operational considerations such as freeze and durability. In this work, the neutron radiography method was used to obtain two-dimensional distributions of liquid water in operating 50 cm 2 fuel cells. Variations were made of flow field channel and diffusion media properties to assess the effects on the overall volume and spatial distribution of accumulated water. Flow field channels with hydrophobic coating retain more water, but the distribution of a greater number of smaller slugs in the channel area improves fuel cell performance at high current density. Channels with triangular geometry retain less water than rectangular channels of the same cross-sectional area, and the water is mostly trapped in the two corners adjacent to the diffusion media. It was also found that cells constructed using diffusion media with lower in-plane gas permeability tended to retain less water. In some cases, large differences in fuel cell performance were observed with very small changes in accumulated water volume, suggesting that flooding within the electrode layer or at the electrode-diffusion media interface is the primary cause of the significant mass transport voltage loss.  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: PEMFC; Flow channels; GDL; Neutron radiography; Water management; Diffusion layer 1. Introduction Hydrogen fuel cells are being developed as highly efficient and cost effective energy conversion devices that potentially have less environmental impact than internal combustion en- gines. The proton exchange membrane fuel cell (PEMFC) is the subject of the majority of fuel cell research, as it can be operated at low temperatures, and thus can be constructed of relatively low cost materials. This will enable the PEMFC to compete in automobile and stationary power generation mar- kets which generally have very stringent cost targets. As PEMFC technology is further refined, it is recognized that several major hurdles must be overcome before current research-scale units are robust enough for commercialization. ∗ Corresponding author. Tel.: +1 585 624 6802; fax: +1 585 624 6680. E-mail address: jon.owejan@gm.com (J.P. Owejan). 0360-3199/$ - see front matter  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.05.044 The focus in the present work is management of the water that is produced in the cathodic oxygen reduction reaction. Because a PEMFC operates at temperatures below 100 ◦ C, liquid water can form throughout the system due to condensation in the porous gas diffusion layers (GDLs) and gas delivery channels. Under steady-state conditions, liquid water accumulation can be minimized by controlling parameters such as inlet relative humidity, temperature, and pressure. However, these parame- ters must be optimized to ensure that a sufficient amount of water is present to maintain membrane and ionomer hydration required for adequate proton conductivity [1]. For automotive applications in particular, the fuel cell stack will rarely be at a steady-state condition, and the power delivery throughout the drive cycle will be quite dynamic. These constant changes in fuel cell power output can cause brief temperature variations, thus influencing the amount of liquid water in the system. For this reason, it is believed that mass transport losses due to