Study of Fuel Cell Stacks Combining Pseudo-3D Multi-Physics Simulations with Experimental Mappings of Current Density and Liquid Water

Abstract

In this work, experimental and numerical analyses of Proton Exchange Membrane Fuel Cell stacks for automotive application are proposed. Performance and durability of PEMFC stacks strongly rely on an optimized water management. An adequate balance has to be found between a sufficient membrane hydration enhancing electrical conductivity and a limited liquid water presence avoiding water flooding. This requires investigations at a local scale inside the cells, because the location of water condensation is not distributed homogeneously in the active area, due to spatial variations of temperature, gas composition or current density.Allowing the quantification of liquid water locally inside PEMFCs, neutron imaging is a powerful tool for the analysis of fuel cell operation at a local scale. It is generally used with single cells and not with stacks, due to the complexity of such experiments. A quantification of liquid water over the active area is obtained through neutron imaging of stacks for several operating conditions. Specific segmented high surface sensors are placed inside stacks to map the current density and temperature distribution in the same area. A multi-physics pseudo-3D two-phase flow model coupling all the electrochemical and transport phenomena supports the understanding of the relationship between all these parameters. The comparison with experimental mappings validates the model, which is able to predict both the current density and the amount of liquid water at a local scale. Unlike experimental measurements that gives a total amount of liquid water in the cell, the model allows to distinguish between anode and cathode sides, or between channels and GDLs, providing crucial information regarding flooding phenomena. Moreover, the flowing direction of the fluids inside the stack have a major influence on liquid water distribution. As a general trend, it is observed that the average total water thickness always decreases when current density increases, in all tested stack flow configurations. Furthermore, a clear relationship appears between flooding, cathode pressure drop and cathode liquid water content. Finally, a detailed analysis is proposed to explain the flooding phenomena, in order to improve the fuel cell stack control. Figure 1