Effects of microstructure characteristics of gas diffusion layer and microporous layer on the performance of PEMFC Chung-Jen Tseng * , Shih-Kun Lo Department of Mechanical Engineering, National Central University, Chungli, Taoyuan 320, Taiwan article info Article history: Received 6 April 2009 Accepted 7 November 2009 Available online 25 November 2009 Keywords: Gas diffusion layer Microporous layer Fuel cell abstract Water management is an important issue in proton exchange membrane (PEM) fuel cell design and oper- ation. The purpose of this work is to investigate the effects of the microstructure characteristics of the gas diffusion layer (GDL) and microporous layer (MPL), including pore size distribution, hydrophobic treat- ment, gas permeability, and other factors, on the water management and performance of a PEM fuel cell. A commercial catalyst-coated membrane with an active area of 25 cm 2 is used along with a GDL and an MPL for assembling a single cell. The effects of the MPL, the thickness of the MPL, the PTFE loading of car- bon paper and MPL, and the baking time of the MPL have been investigated. Results show that the addi- tion of MPL increases cell performance in the high current density region due to the elimination of mass transfer limitation. There exists an optimum thickness of MPL. Furthermore, increasing the MPL baking time enhances cell performance due to enlarged pore size and permeability. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Proton exchange membrane fuel cells (PEMFCs) convert the chemical energy of a fuel directly into electricity in an electro- chemical reaction. PEMFCs are a viable alternative for environ- ment-friendly and efficient power production and have a wide range of potential applications. In terms of environmental and glo- bal energy problems, the replacement of fossil fuels by renewable energy is being considered all over the world. The fuel cell as a re- vived energy technology is believed to be an ideal energy system because of its high conversion efficiency and excellent regenerative and zero-emission properties. However, like many emerging en- ergy technologies, PEMFCs must overcome certain engineering and economic obstacles if they are to ever become commercially and popularly viable. Therefore, in order to ensure, without spatial concession, high power for a commercial-scale system, it is pre- dicted that fuel cell operation at high current density conditions per unit electrode area will be necessary. Fig. 1 depicts the schematic diagram of the configuration and mass transport mechanism in the membrane electrode assembly (MEA) and flow channels. Water vapor or liquid water, along with hydrogen and oxygen gases, enters and exits through the diffusion path in the electrode. Electrodes for a PEMFC have, in general, two- or three-layered structures that can be divided into two parts, one catalytic and the other noncatalytic. The catalytic part is the cata- lyst layer. It is formed by depositing a mixture of a carbon-sup- ported platinum catalyst. A hydrophobic gas diffusion layer (GDL) and sometimes an additional microporous layer (MPL) are placed between the catalyst layer and the flow channel plate. Although the GDL and MPL have no electrochemical reaction sites, they are known to play an important role in providing the reac- tants a good access to the catalytic sites and in the effective re- moval of product water from the electrode. Mass transport problems in a PEMFC can be classified into three categories: (1) water flooding, i.e., the liquid water entrapped inside the electrodes or flow channels interrupts the flux of the reactant/ product gases; (2) dilution of oxidant concentration due to the use of air instead of pure oxygen; and (3) depletion of reactants along the flow channel, which results in a nonuniform current distribution over the whole electrode area and is particularly severe in a large- scale fuel cell [1]. Appropriate water management is critical in order to obtain a stable cell performance of the PEMFC. On one hand, water is needed to hydrate the ionically conducting membrane and the ionic conductor in the catalyst layer for proton conductance. That is, the higher the water content, the better is the ionic conduc- tivity. Water can be introduced by external humidification and as a product of the oxygen reduction reaction at the cathode side. On the other hand, this water can flood the pores in the catalyst layers as well as those in the gas diffusion layers, resulting in a higher mass transport resistance. That is, the less the water content, the lower is the resistance to reactant flow. Clearly, water plays a conflicting role; therefore, appropriate water management is required. The GDL is usually made of either a nonwoven carbon paper or a woven carbon cloth due to its high porosity and electric conductivity. Even if the MEA based on a carbon cloth has a higher 0196-8904/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2009.11.011 * Corresponding author. Tel.: +886 3 4267348. E-mail address: cjtseng@ncu.edu.tw (C.-J. Tseng). Energy Conversion and Management 51 (2010) 677–684 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman