Application of a CFD Methodology for the Design of PEM Fuel Cell at the Channel Scale

Polymer electrolyte membrane (PEM) fuel cells will play a crucial role in the decarbonization of the transport sector, in particular for heavy duty applications. However, performance and durability of PEMFC stacks is still a concern especially when operated under high power density conditions, as required in order to improve the compactness and to reduce the cost of the system. In this context, the optimization of the geometry of hydrogen and air distributors represents a key factor to improve the distribution of the reactants on the active surface, in order to guarantee a proper water management and avoiding membrane dehydration. To this purpose, the adoption of CFD simulation tools can provide a useful insight into the physical phenomena which determine the efficient operation of the fuel cell (e.g. transport of mass, heat, species, electrons and ions, electrochemical reactions, water formation and removal), providing a valuable support for the design and the optimization of the device at the channel scale. In this work, an open-source simulation library, based on the OpenFOAM code, is applied to the detailed simulation of a basic module of a PEM fuel cell arranged with simple parallel channels. The simulation methodology is based on a multi-region and multi-physics approach, where the different components of the fuel cell (namely air and fuel channels, gas diffusion layers, catalyst layers, bipolar plates) are modeled resorting to different computational grids defining different local domains, on which the specific governing equations are solved. Transport phenomena in all of the local domains are coupled and solved simultaneously. The model is firstly validated resorting to experimental data acquired on a specific test bench installed at Politecnico di Milano. Then, a detailed analysis of the flow field is conducted in order to provide guidelines for the optimization of the distributor geometry. Finally, the influence of the channel design on the fuel cell performances is investigated, highlighting the influence of the rib-to-channel width geometrical parameter on the reactants diffusion and water removal.