Patent ID: 7781112

Claim:
A method of operating a reversible fuel cell system, comprising cyclically operating the reversible fuel cell system in a fuel cell mode to generate electrical energy and reactant product from fuel and an oxidizer at a first equilibrium temperature and in an electrolysis mode to generate the fuel and an oxidant from the reactant product and the electrical energy at a second equilibrium temperature; providing excess reactant product to the reversible fuel cell system operating in the electrolysis mode from outside the reversible fuel cell system, in addition to or instead of the reactant product generated by the reversible fuel cell system in the fuel cell mode, such that fuel in excess of fuel required to operate the reversible fuel cell system in the fuel cell mode is generated in the electrolysis mode over a predetermined number of operating cycles; and removing the excess fuel generated by the reversible fuel cell system operating in the electrolysis mode from an electrochemical system in which the reversible fuel cell system is located; wherein the first equilibrium temperature is different from the second equilibrium temperature.