Effects of various operating and initial conditions on cold start performance of polymer electrolyte membrane fuel cells

Cold start is a challenging and important issue that hinders the commercialization of polymer electrolyte membrane fuel cell (PEMFC). In this study, a three-dimensional multiphase model has been developed to simulate the cold start processes in a PEMFC. Numerical simulations have been conducted for a single PEMFC starting at various operating and initial conditions, which are cell voltages, initial water contents and distributions, anode inlet relative humidity (RH), surrounding heat transfer coefficients, and cell temperatures. It is found that the heating-up time can be significantly reduced by decreasing the cell voltage and effective purge is critical for PEMFC cold start. The largest heating source at high cell voltages is the activational heat, and it becomes the ohmic heat at low cell voltages. The water freezing in the membrane is not observed when the cell is producing current due to the heat generation and the slow water diffusion into the membrane at subzero temperatures, and it is only observed after the cold start is failed, further confirming the importance of purge. Humidification of the supplied hydrogen has negligible effect on the cold start performance since only small amounts of water vapour can be taken by the gas streams at subzero temperatures. The surrounding heat transfer coefficients have significant influence on the heating-up time, indicating the importance of cell insulation or heating. The rate of cell heating up is reduced when the startup temperature is lowered due to the more sluggish electrochemical reaction kinetics.