Eurotherm Seminar N° 81 Reactive Heat Transfer in Porous Media, Ecole des Mines d’Albi, France June 4 – 6, 2007 ET81 – 21 Simulation of multiphase multicomponent processes in the diffusion layer of fuel-cells Steffen Oliver Ochs Lehrstuhl für Hydromechanik und Hydrosystemmodellierung (LH2), Universität Stuttgart steffen.ochs@iws.uni-stuttgart.de Holger Class Lehrstuhl für Hydromechanik und Hydrosystemmodellierung (LH2), Universität Stuttgart holger.class@iws.uni-stuttgart.de Rainer Helmig Lehrstuhl für Hydromechanik und Hydrosystemmodellierung (LH2), Universität Stuttgart rainer.helmig@iws.uni-stuttgart.de Maria Acosta Formerly Institut für Chemische Verfahrenstechnik (ICV), Universität Stuttgart acosta@icv.uni-stuttgart.de Abstract. The development of new alternative power sources/supplies is an important task nowadays. Polymer electrolyte membrane (PEM) fuel-cells are currently intensively investigated and improved for applications. It has been found that the kinetics of oxygen reduction and hence the transport of oxygen in the gas diffusion layer of PEM fuel-cells is a limiting factor for their performance. Especially water generated at the cathode has been found to constrain the oxygen transport in the reaction layer. Thus an efficient water management is essential to improve the performance of PEM fuel-cells. This requires a profound understanding of the physical and electrochemical processes in the cathode a PEM fuel-cell. In this paper we show how multiphase multicomponent model,s originally developed for the simulation of non-isothermal multiphase processes in porous media, are adopted to model the oxygen transport in the diffusion layer of PEM fuel-cells. Along with this, results of some simulation runs will be discussed focusing on the oxygen transport in the diffusion layer. Finally further research activities planed at the Lehrstuhl für Hydromechanik und Hydrosystemmodellierung (LH2) in this field are discussed. Keywords. multiphase, multicomponent, simulation, PEM fuel-cell, water management 1. Introduction Polymer elecrolyte membrane (PEM) fuel-cells are very promosing for the application as an alternative energy supply system in portable devices or vehicles. Their usually low operation temperature (T<100°C) is one of their major advantages compared to other fuel-cell types. However, further research is required to improve their performance and to make them competitive with conventional energy supply systems. This requires an improved understanding of the relevant physical and electrochemical processes and especially those that are performance-limiting in order to take adequate measures to overcome these limitations. The general assembly of a PEM fuell-cell comprises of a proton conduction polymer membrane which is situated between two porous catalytic electrodes. The electrodes consist a porous diffusion layer (DL) and a reactive layer containing a catalyst (e.g. Platinum). This mebrane-electrode-assembly (MEA) is placed between two cell plates providing electrical connection and generating a flow field necessary to supply the reactants to the reaction layer and the removal of excess products from the cell. It is a well accepted fact that the cathode is the limiting compount of a hydrogen PEM fuel-cell, due to the slow kinetics of the oxygen reduction reaction and the transport limitations of oxygen to the reaction layer (see Springer et al. (1993)). The chemical reactions in a fuell are: Anode: H 2 2H + + 2e - Cathode: 1/2O 2 + 2H + + 2e - H 2 0 Overall: H 2 + 1/2O 2 H 2 O Water formed at the cathode of the fuel cell hinders the oxygen transport to the catalyst layer and hence has a negative impact on the overall performance of the fuell cell. Therefore the management of excess water is a critical factor in the fuel cell development . This is because the membrane of the fuel cells has to be humidified in oder to enable the transport of protons from the anode to the cathode etectrode on the other hand excess water in the diffusion layer does hinder the transport of oxygen via diffusion layer to the reaction layer s. For increasing the efficeny of a fuel cell