Patent ID: 6969564

Claim:
A fuel cell stack comprising a cell assembly comprising a stack of unit cells each having a membrane electrode assembly which comprises an anode, a cathode, and a solid polymer ion exchange membrane sandwiched between the anode and the cathode, said cell assembly having: a plurality of reactant gas passages connected in series in the unit cells each passing a reactant gas, which is one of a fuel gas and an oxygen gas, along electric energy generating surfaces of said unit cells; a plurality of reactant gas inlets defined in the unit cells, respectively, for supplying said reactant gas to said reactant gas passages; and a plurality of reactant gas outlets defined in the unit cells, respectively, for discharging said reactant gas from said reactant gas passages; said reactant gas inlets being disposed upwardly of said reactant gas outlets, said reactant gas outlets being disposed at least partly below said electric energy generating surfaces of said unit cells, wherein said cell assembly has intermediate communication holes providing communication between the reactant gas passage in an upstream unit cell of the unit cells and the reactant gas passage in a downstream unit cell of the unit cells, said intermediate communication holes including intermediate reactant gas outlets for discharging the reactant gas from the reactant gas passage in the upstream unit cell and intermediate reactant gas inlets for supplying the reactant gas to the reactant gas passage in the downstream unit cell, said intermediate reactant gas outlets being disposed below said intermediate reactant gas inlets and disposed at least partly below said electric energy generating surfaces of said unit cells.