Effect of the pore structure of cathode catalyst layer on the PEM fuel cell cold start process

A transient numerical model was developed to investigate the effect of the pore structure in the cathode catalyst layer on the cold start process of polymer electrolyte fuel cells. The results prove the necessity of considering the subcooled water at subzero temperatures when simulating the cold start of fuel cells based on the Gibbs-Thomson effect. At ambient temperatures lower than −13 °C, the ice blockage is found to occur inside the cathode catalyst layer (CCL). However, due to the generation and flow of the subcooled water, the blockage occurs at the CCL and cathode microporous layer (CMPL) interface at a temperature higher than −13 °C. The pore size of the CCL also plays an important role in the cold start of PEM fuel cells, and there exists a critical pore size to shift the blockage location from the interior of the CCL to the CCL/CMPL interface. The CCL with this critical pore size gives the fuel cell the best cold start capability. It is also worth noting that the actual pore size distribution of the CCL complicates the blocking mechanisms in the fuel cell and remarkably influences the cold start simulation, especially at an operating temperature higher than −12 °C.