PEM fuel cell with high porosity water transport plates and temperature increase before shut down in subfreezing conditions

摘要

A fuel cell stack (50) includes fuel cells (16, 18, 19) with anode and cathode water transport plates (23, 31, 34, 37) having porosity of at least 50%, thereby to significantly increase the amount of water stored within the water transport plates when the stack is shut down, which doubles the heat of fusion as the ice in the pores melts during a startup following freeze. This extends the period of time before the water in the pores reaches a hard freeze at −20° C. from 180 hours to 280 hours. A controller (60) controls the bypass (55) of a heat exchanger (54) to cause the temperature of the stack to reach a temperature sufficient to raise the sensible heat of the stack by 20%-40% above what it is with the fuel cell power plant operating steady state, prior to being shut down, thereby increasing the hours required for the fuel cell to cool down to 0° C. in −20° C. environment from 60 hours to 90 hours, allowing easier startups when shut down for less than 90 hours.