Patent ID: 8470486

Claim:
A fuel cell system, comprising: a fuel cell stack in which a plurality of fuel cells are stacked in one or more groups of fuel cells, each fuel cell including a fuel electrode to which fuel gas containing hydrogen is supplied at a fuel gas supply pressure, an oxidizing electrode to which oxidizing gas containing oxygen is supplied at an oxidizing gas supply pressure, and an electrolyte membrane disposed between the fuel electrode and the oxidizing electrode, the membrane having a fuel-electrode side and an oxidizing-electrode side; a pressure-difference control unit programmed to generate a pressure difference across the membrane between the fuel electrode and the oxidizing electrode in each fuel cell and for changing the pressure difference, the pressure difference being such that the pressure at the fuel electrode is higher than the pressure at the oxidizing electrode; a cell-voltage measuring device for measuring a cell voltage of each fuel cell or each group of fuel cells in the fuel cell stack; and a leakage determination unit programmed to determine the presence or absence of a leaking cell based on the behavior of the cell voltage of each fuel cell as measured by the cell-voltage measuring device while the pressure-difference control unit gradually increases the pressure difference with time, a leaking cell being a fuel cell in which gas flows through the electrolyte membrane from the fuel-electrode side to the oxidizing-electrode side, wherein the pressure-difference control unit is programmed to adjust one or both of the fuel gas supply pressure and the oxidizing gas supply pressure from a state in which the fuel gas pressure at a fuel electrode inlet is substantially equal to the oxidizing gas supply pressure at an oxidizing gas supply inlet to increase the pressure difference monotonically by reducing the oxidizing gas supply pressure to achieve a predetermined pressure difference, and wherein the leakage determination unit is programmed to monitor the cell voltage during the monotonic increase in pressure difference to determine the presence or absence of a leaking cell.