Fuel cell stacks are electrochemical devices that produce water and an electric potential from a fuel, which typically is a proton-liberating source, and an oxidant. Many conventional fuel cell stacks utilize hydrogen gas as the proton source and oxygen, air, or oxygen-enriched air as the oxidant. Fuel cell stacks typically include many fuels cells that are fluidly and electrically coupled together, often between common end plates. The fuel cell stack receives flows of hydrogen gas and air from suitable sources and distributes these flows to the individual fuel cells in the stack. The fuel cell stack includes manifolds and other delivery conduits to deliver and remove fluids to and from the fuel cells within the fuel cell stack. Conventionally, a fuel cell stack includes current collectors that are adapted to be electrically connected to an external load so that the electrical output produced by the fuel cell stack may be used to satisfy the applied external load.
The fuel cells in the fuel cell stack include anode and cathode regions that are separated by an electrolytic barrier, which may take the form of an electrolytic membrane. Hydrogen gas is delivered to the anode region, and oxygen gas is delivered to the cathode region. Protons from the hydrogen gas are drawn through the electrolytic membrane to the anode region, where water is formed. Conventionally, the anode and cathode regions are periodically or continuously purged to remove water and accumulated gases in these regions. While protons may pass through the membranes, electrons cannot. Instead, the electrons that are liberated by the passing of the protons through the membranes travel through an external circuit to form an electric current.
A factor that affects the performance, or efficiency, of a fuel cell stack to produce an electric current is the temperature of the stack. Accordingly, it is desirable to maintain the fuel cell stack within a range of suitable operating temperatures, such as within upper and lower threshold temperatures. During startup, the stack may not be at a temperature within this desired temperature range, and in such a situation, it is desirable to transition the stack to a temperature within this range. Maintaining and/or starting up a fuel cell stack in subfreezing temperatures is more difficult because the liquid heat exchange fluid may be frozen or freeze when drawn from a reservoir for delivery to the fuel cell stack.