Patent ID: 8916307

Claim:
A fuel cell system comprising: a fuel cell having a membrane-electrode assembly in which both surfaces of an electrolyte membrane are sandwiched between a pair of catalyst layers, the fuel cell being supplied with reactant gas to generate electric power through an electrochemical reaction of the reactant gas; an impedance calculation part is programmed to calculate a first impedance which is an impedance of the fuel cell in a first frequency range and which corresponds to resistance of the electrolyte membrane, and also calculates a second impedance which is an impedance of the fuel cell in a second frequency range which is lower than the first frequency range; the second impedance corresponding to the sum of resistance of the electrolyte membrane and resistance of the catalyst layer; and a water content calculation part is programmed to calculate a differential impedance which is a difference between the second impedance and the first impedance, and, by referring to a correlation between the differential impedance and water content of the catalyst layer, the correlation having been stored in a memory in advance, calculates the water content of the catalyst layer that corresponds to the calculated differential impedance.