Unitized regenerative fuel cell system

A unitized regenerative fuel cell (URFC) system that operates either in a fuel cell mode while discharging or in an electrolytic cell mode when charging comprising first and second reactant gas storage tanks, a water storage reservoir, and a fuel cell stack, comprising:

• first and second reactant gas feed lines communicating between the fuel cell stack and the first and second reactant gas storage tanks for conveying reactant gases from the fuel cell stack to the first and second reactant gas storage tanks and for returning reactant gases from the first and second reactant gas storage tanks to the fuel cell stack:
• the first and second reactant gas storage tanks acting as heat sinks and radiators of waste heat to an ambient environment below 0° C. so that during the electrolytic cell mode the surface temperature of the first and second reactant gas storage tanks is below 0° C. and during the fuel cell mode the tank surface temperature of the first and second reactant gas storage tanks is above freezing temperature;
• first and second heat pipes thermally communicating with said fuel cell stack and first and second reactant gas storage tanks, respectively for conveying waste heat from the fuel cell stack to the surface of the first and second reactant gas storage tanks;
• first and second reactant gas dryers in thermal communication with the first and second reactant gas storage tanks, respectively, and disposed within the first and second reactant gas feed lines, respectively, each of the first and second reactant gas dryers is integral with a surface of the first and second reactant gas storage tanks, respectively;
• whereby reactant gases conveyed from the fuel cell stack to the first and second reactant gas storage tanks during the electrolytic cell mode give up energy to storage tanks so that water vapor mixed with the reactant gases condenses out and freezes on internal gas dryer surfaces and during the fuel cell mode reactant gases passing from the first and second reactant gas storage tanks through the first and second reactant gas dryers on their way to the fuel cell stack are heated by the first and second reactant gas storage tanks from heat generated by the fuel cell stack whereby water on the internal gas dryer surfaces melts and returns to the reactant gases flowing to the fuel cell stack;
• an expandable water storage reservoir formed as a bellows contained within a pressure dome, said water storage reservoir having water stored inside the bellows and being connected to the fuel cell stack for allowing the water volume inside the bellows to expand or contract depending upon the operation of the fuel cell stack;
• and
• a gas pressure line communicating between the first reactant gas feed lines and the pressure dome that contains the expandable water storage reservoir for directing pressurized gas from the first reactant gas storage tank into the pressure dome and outside of the bellows so that the water pressure in the bellows is less than the gas pressure outside of the bellows.