Patent ID: 8492043

Claim:
A fuel cell system comprising: a fuel cell including: a plurality of cell blocks, each of which is formed by stacking cells, each of the cells including a pair of electrodes and a polymer electrolyte layer sandwiched between the pair of electrodes; a cell block internal fuel gas channel which penetrates each of the cell blocks and through which a fuel gas flows so as to flow through the cells of the cell block; a cell block internal oxidizing gas channel which penetrates each of the cell blocks and through which an oxidizing gas flows so as to flow through the cells of the cell block; a cell block internal cooling medium channel which penetrates each of the cell blocks and through which a cooling medium flows so as to flow through the cells of the cell block; a cooling medium connecting channel connecting the cell block internal cooling medium channel of one of the cell blocks and the cell block internal cooling medium channel of the other cell block in series; a fuel gas supplying device configured to supply the fuel gas to the fuel cell; an oxidizing as supplying device configured to supply the oxidizing as to the fuel cell; a temperature controller configured to control a temperature of the fuel cell; an electric power adjuster configured to adjust electric power obtained from the fuel cell; and a controller configured to control the fuel gas supplying device, the oxidizing gas supplying device, the temperature controller, and the electric power adjuster, wherein: at least one of the pair of electrode includes a catalyst layer, the catalyst layer includes a catalyst support and a polymer electrolyte material adhered to the catalyst support, the catalyst support containing an electrode catalyst and carbon powder supporting the electrode catalyst, the catalyst layer in the cells of a cooling medium downstream cell block located downstream of the cooling medium connecting channel is higher or larger in at least one selected from the group consisting of a density of an ion exchange group per unit volume of the catalyst layer, an electrode catalyst supporting amount of the catalyst support of the catalyst layer, and a catalyst supporting rate of the catalyst layer, than the catalyst layer in the cells of a cooling medium upstream cell block located upstream of the cooling medium connecting channel, and the controller is configured to carry out an electric power generating operation under such conditions that a relative humidity of the fuel gas flowing through the cell block internal fuel gas channel of the cooling medium downstream cell block is lower than that of the fuel gas flowing through the cell block internal fuel gas channel of the cooling medium upstream cell block and a relative humidity of the oxidizing gas flowing through the cell block internal oxidizing gas channel of the cooling medium downstream cell block is lower than that of the oxidizing gas flowing through the cell block internal oxidizing gas channel of the cooling medium upstream cell block.