Patent ID: 7090941

Claim:
A fuel cell stack including a cell assembly of unit cells stacked together, said unit cells each having a membrane electrode assembly including an anode, a cathode, and an electrolyte interposed between said anode and said cathode, said unit cells having reactant gas flow passages therein for supplying a reactant gas along a reactant surface thereof, said reactant gas including at least one of a fuel gas and an oxygen-containing gas, and said unit cells including an upstream unit cell and a downstream unit cell, wherein said reactant gas flow passages are connected in series by communicating an outlet of said reactant gas flow passage of said upstream unit cell and an inlet of said reactant gas flow passage of said downstream unit cell by a communicating reactant gas passage, wherein an additional reactant gas is supplied to said communicating reactant gas passage, wherein a reactant gas supply passage and a return passage extend through said cell assembly, said return passage connecting said communicating reactant gas passage and said reactant gas supply passage, and said reactant gas discharged from said upstream unit cell flows through said return passage and flows into said reactant gas supply passage of said downstream unit cell.