Experimental study of cold start of PEM fuel cell with non-uniform metal foam flow field

In proton exchange membrane (PEM) fuel cells, non-uniform metal foam flow fields (MFFFs) can improve the cell performance by mitigating the issues of weak diffusion and low velocity. Previous studies primarily consider non-uniform MFFFs under normal operating conditions. Whether the non-uniform design can leverage its advantages in sub-zero environments remains unclear. In this study, non-uniform MF structures are explored experimentally, analyzing the effects of MF pore size gradients on the cold start performance. The results indicate that non-uniform MFFFs with the pore size increasing from the GDL to the MFFF in the through-plane (TP) direction and decreasing from the inlet to the outlet in the in-plane (IP) direction exhibit better cold start performance. In the TP direction, larger pores in the upper layers can facilitate liquid water removal and promote reactant gas transport into the electrode, while smaller pores in the lower layers can reduce the probability of interfacial ice formation due to supercooled water. In the IP direction, reducing the pore size in the downstream can prolong the residence time of reactant gases in the downstream, enhance the gas convection in the TP direction, increase the heat generation of electrochemical reactions, and thus alleviate the severe icing issues at the downstream of the cell.