Determination of Local Conditions in PEFCs by Combining Spatially Resolved Current Density Measurements with Real-time Modeling

Abstract

One of the major challenges in the development of polymer electrolyte fuel cells (PEFCs) is to exploit the whole capacity that inheres a given membrane electrode assembly (MEA). In practice, certain obstacles remain to be overcome like the water management and the corresponding local mass transport effects. These parameters lead to inhomogeneous current distributions, which reduce the efficiency of a MEA and hence that of a PEFC. In order to investigate factors limiting the performance, the DLR has developed several measurement and visualization techniques to determine the local current density distribution in fuel cells without interfering the cell operation [1-5]. For getting detailed information about the origin of these local effects, the DLR has improved one of these techniques by implementing an isothermal model for the calculation of the cathodic gas flow along the flow field channels. Within the model, the composition (including the content of liquid water), the average gas velocity, the pressure drop and other quantities can be calculated for different gas distributor structures in real-time. These calculations base on several input parameters which have to be determined by experiment at the same time, e.g. the water content of the feed gas and the local current density. In addition the model needs no parameters for adjustment. The combination of a spatially resolved measurement technique with a real-time simulation is a helpful tool for the development of fuel cell components as well as for the optimization of the operating conditions. In this presentation, the results of several experimental investigations and the corresponding simulations for a 25 cm2 serpentine flow field at different operation modes will be shown.