An electric power generation system has elements that improve the cold
start capability and freeze tolerance of a constituent fuel cell stack
cooperate to reduce the amount of water remaining within the passages of
the stack. The system includes a purge system that is connectable to the
oxidant supply, fuel supply and/or coolant passages upstream of the
stack. When the stack is shut down, the stack is disconnected from an
external circuit, and purge fluid is transmitted by the purge system
through the stack before the stack falls below the freezing point of
water. In systems where fuel and/or oxidant streams are humidified prior
to entry into the stack, a humidifier bypass system may be provided in
place of the purge system. The humidifier bypass system transmits
reactant fluid to the stack in fluid isolation from the humidifier, so
that the inlet reactant streams are unhumidified.