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Operation of proton exchange membrane fuel cells at high current densities is a potential option to reduce fuel cell cost and volume for automotive applications. This operating regime was investigated using low cell voltages leading to limiting current density values. A zero-dimensional cell voltage model and a one-dimensional low cell voltage model were developed and validated. The operating conditions required for model applicability were summarized. The gas diffusion electrode overall mass transfer coefficient was identified as a key design parameter. [ABSTRACT FROM AUTHOR]

Simultaneous heat and mass transfer in the porous cathode of a proton exchange membrane (PEM) fuel cell is generated by the exothermic chemical reaction at the catalyst layer. A two-dimensional steady state model in a cross section of the porous electrode taken normal to the gas flow in the channels is presented. We consider a multicomponent inlet feed composed of oxygen, nitrogen, and water vapor on the cathode side. The mathematical formulation reduces to a system of four nonlinear second-order elliptic partial differential equations subject to appropriate nonlinear boundary conditions. Numerical solutions are obtained using a finite-difference method. Results are presented for various operating conditions and design parameters in order to identify the important factors in the performance of the fuel cell. From the calculated values of the vapour pressure and temperature, the regions of vapor oversaturation are identified. [ABSTRACT FROM AUTHOR]

Abstract: A macroscopic model for a non-isothermal cathode catalyst layer (CL) in a proton exchange membrane (PEM) fuel cell is presented, in which liquid water in the CL pores is neglected. The model couples three phases: an electrically conductive carbon/platinum phase, gas pores, and a proton-conducting Nafion phase. The reaction–diffusion dynamics are described by a nonlinear system of differential equations which, due to the wide range of physical parameters, is very stiff. To reduce the stiffness of the system, an appropriate scaled model is introduced. A numerical algorithm consisting of two embedded Newton loops, specifically developed to handle the stiffness, is presented. Several numerical results are used to investigate the dynamics of the layer and the validity of the interface reduction, or zero CL thickness limit, which is often used in large fuel cell computations. In the limit of infinite water adsorption rate between ionomer phase and pore, a boundary layer emerges at either side of the CL, in which the water sorption equilibrium [Zawodzinski, T., Derouin, C., Radzinski, S., Sherman, R., Smith, V., Springer T., Gottesfeld, S., 1993. A comparative study of water uptake by and transport through ionomeric fuel cell membranes. Journal of the Electrochemical Society 140, 1981–1985] between ionomer and pore is violated. [Copyright &y& Elsevier]

Abstract: Stack models require consideration of interactions between cells owing to practical variation of cell model parameters and different location/environment in the stack leading to thermal, electrical and mass transfer gradients. A previously developed voltage/current distribution model (electrical interaction) was extended and validated using two types of anomalies (bus plate material change, partially inactive cell located at the stack center), two anomaly locations and one or two anomalies within the stack. A measurement method for the principal cell interaction damping factor is discussed which can be used to easily and approximately predict the number of cells that are impacted by an anomaly. [Copyright &y& Elsevier]

Abstract: In this paper, we present a comprehensive non-isothermal, one-dimensional model of the cathode side of a Polymer Electrolyte Fuel Cell. We explicitly include the catalyst layer, gas diffusion layer and the membrane. The catalyst layer and gas diffusion layer are characterized by several measurable microstructural parameters. We model all three phases of water, with a view to capturing the effect that each has on the performance of the cell. A comparison with experiment is presented, demonstrating excellent agreement, particularly with regard to the effects of water activity in the channels and how it impacts flooding and membrane hydration. We present several results pertaining to the effects of water on the current density (or cell voltage), demonstrating the role of micro-structure, liquid water removal from the channel, water activity, membrane and gas diffusion layer thickness and channel temperature. These results provide an indication of the changes that are required to achieve optimal performance through improved water management and MEA-component design. Moreover, with its level of detail, the model we develop forms an excellent basis for a multi-dimensional model of the entire membrane electrode assembly. [Copyright &y& Elsevier]