Patent ID: 7695848

Claim:
A fuel cell stack comprising a plurality of stacked fuel cell units, each of the fuel cell units comprising a membrane electrode assembly in which a fuel electrode and an oxidizer electrode are disposed on both sides of a polymer electrolyte membrane; an oxidizer flow path forming member, which is disposed on the oxidizer electrode side of the membrane electrode assembly and includes an opening for supplying an oxidizer therethrough; and a separator disposed in contact with a surface opposite to a surface being in contact with the oxidizer electrode of the oxidizer flow path forming member, wherein at least one of the plurality of fuel cell units constituting the fuel cell stack includes a water absorbing member having a surface exposed to the atmosphere in a portion where the oxidizer flow path forming member and the separator are in contact with each other, and wherein an area of the surface exposed to the atmosphere of the water absorbing member of the fuel cell unit whose temperature becomes relatively lower of the plurality of fuel cell units constituting the fuel cell stack is larger than an area exposed to the atmosphere of the water absorbing member of the fuel cell unit whose temperature becomes relatively higher.