Coupled stress–strain and transport in proton exchange membrane fuel cell with metallic bipolar plates

Abstract

Metallic bipolar plates (BPPs) for proton-exchange membrane fuel cells (PEMFCs) are desirable in automotive applications because they (i) offer good mechanical properties and manufacturability, (ii) reduce costs compared with graphite-based BPPs, and (iii) allow flexible flow-channel designs that increase power density. In this study, the relatively unexplored couplings between the mechanical and electrochemical effects due to stack compression were analyzed using a model that accounts for the transport, electrochemical reaction, heat transfer, and stress mechanics. The present model is aimed to be employed into simulation tools for PEMFC design and application. Both the tilt angle and flow-channel width of the BPPs were found to affect the stress distribution in the gas-diffusion layer (GDL) and BPP, as well as the contact resistance. The coolant pressure affected the stress distribution in the BPP, particularly at the welded joint between two adjacent plates. Stack compression not only increased the mass-transfer resistance of the GDL, particularly under the rib region, but also resulted in improved heat transfer, which reduced the PEMFC temperature and improved the uniform temperature distribution. Although the impacts of compression on the heat and mass transfer became more pronounced at higher current densities, the combined effect with the reduced membrane temperature and contact resistance between the GDL and BPP resulted in improved PEMFC performance. Applying the model to investigate a range of mechano-electrochemical conditions revealed that higher stress–strain concentrations resulted in a more nonuniform current–density distribution at the interface between the microporous layer and catalyst layer.