Patent ID: 7799478

Claim:
A fuel cell including a plurality of electricity generating units, each electricity generating unit being comprised of one or more membrane electrode assemblies, each membrane electrode assembly comprised of an electrolyte, a fuel electrode, and an air electrode, and wherein the first and second electricity generating units are arranged serially in a direction of fuel flow, the fuel cell comprising: an upstream-side generating section comprised of electricity generating units located at an upstream-side in a direction of flow of fuel, a downstream-side generating section comprised of electricity generating units located at a downstream-side in the direction of flow of fuel, and a fuel concentration adjusting section for adjusting a concentration of fuel supplied to at least one of the upstream-side and downstream-side generating sections based upon a relative amount of output power density between the generating sections, wherein the fuel concentration adjusting section is adapted to set the fuel concentration to a higher value if the output power density at the upstream-side generating section is higher than that of the downstream-side generating section.