Patent ID: 7563526

Claim:
A fuel cell system which generates electricity by supplying fuel gas and oxidant gas to a fuel cell stack comprising: a fuel cell stack comprising water as a by-product of a reaction between fuel gas and oxidant gas, a plurality of unit cells, each unit cell including a membrane electrode assembly to generate electricity from the reaction between the fuel gas and oxidant gas, which forms the water as a by-product, the membrane electrode assembly comprising a polymer electrolyte membrane and two electrodes on both sides of and adjacent to the polymer electrolyte membrane, a fuel cell stack anode electrically connected to one of the two electrodes, and a fuel cell stack cathode electrically connected to the other of the two electrodes, wherein each unit cell is immediately adjacent another unit cell; a rechargeable battery electrically connected to the fuel cell stack in a parallel connection in which an anode of the battery is electrically connected to the anode of the fuel cell stack, and a cathode of the battery is electrically connected to the cathode of the fuel cell stack, the battery supplies current to the unit cells of the fuel cell stack through the parallel connection to allow the unit cells to electrolyze water therein; and a controller programmed to: determine whether or not the fuel cell stack is generating electricity, and supply current to the unit cells of the fuel cell stack from the battery through the parallel connection to allow the unit cells to electrolyze the water therein, when generation of electricity by the fuel cell stack is terminated, and supply current from the unit cells through the parallel connection to charge the battery when the fuel cell stack generates electricity.