Experimental studies on the influence of operational parameters on the cold start of a 2 kW fuel cell

In this paper, experimental investigations on the influence of operational parameters on PEM fuel cell cold start are presented, The effect of current density, stack impedance at 1 kHz prior to start, as well as gas flow rate, gas pressure, coolant flow rate and surrounding subfreezing temperature are studied. The experimental apparatus is briefly described. It includes a main unit at room temperature and a smaller separate unit in a climatic chamber. Low current density, high impedance prior to start, moderate subfreezing temperature (-5 degrees C), high gas flow rate, low gas pressure and low coolant flow rate are found to have a positive impact on the cold start performance. Combining these parameters, self start-up of the fuel cell without additional energy is achieved at -5 degrees C in 30 min. The whole set of observations leads to the following hypotheses on freeze mechanism: in the first phase, dry membranes and low current lead to a transient phase of membrane humidification. Then, in the second phase, ice clogging of the active layers occurs. In the third phase, a variable quantity of the produced water reaches the gas diffusion layers and channels.