Effect of gas diffusion layer parameters on cold start of PEMFCs with metal foam flow field

Metal foam (MF) flow field has extensive potential in proton exchange membrane fuel cells (PEMFCs). Under its influences on the internal flow and heat/mass transfer in PEMFCs, the original electrode structure base on the “channel-rib” flow field could be no longer suitable. In this study, the effects of gas diffusion layer (GDL) parameters on the cold start of PEMFCs with MF flow fields are studied experimentally. We focus on the pore size distribution and hydrophobicity of the GDL and investigate their effects on the cold start performance, the cell impedance, and the cell degradation. The results show that GDLs with large pore diameter and smooth pore size gradient are helpful to enhance the cold start performance and reduce the cell degradation due to the small mass-transfer resistance and excellent water/ice-storage capacity. In addition, the cell of GDL with moderate hydrophobicity has the best cold start performance at -5 °C as it can well balance the resistance of water transfer in GDL and from CL into GDL. Below -5 °C, a stronger GDL hydrophobicity can lead to a longer cell operating time and better cell stability. This is mainly because the GDL hydrophobicity can significantly affect the reactant flow path and the internal water freezing. The results of this study provide physical insight into the electrode optimization for improving the cold start of PEMFCs with MF flow fields.