Heretofore, a fuel cell is known which generates power by making a fuel gas (hydrogen, for example) supplied to a fuel electrode and an oxidant gas (the air, for example) supplied to an oxidant electrode electrochemically react with each other. In a fuel cell system including the fuel cell, the air is sometimes present in both the oxidant electrode and the fuel electrode at a start-up. In this case, a boundary between the air present in the fuel electrode and hydrogen newly supplied thereto, so-called a hydrogen front may deteriorate the fuel cell. More specifically, corrosion of a carbon support supporting a catalyst of platinum or the like may possibly occur.
For example, Patent Literature 1 discloses a shutdown method for fuel cell. According to this method, oxygen and hydrogen in the fuel cell are made to react with each other with the air flow to the oxidant electrode being shut off. Thereby, the concentration of oxygen remaining in the oxidant electrode is reduced and the concentration of hydrogen in the fuel cell is increased until no oxygen remains in the fuel electrode and the oxidant electrode and the gas composition within the fuel electrode and the oxidant electrode comes to an equilibrium gas composition of at least 0.0001% hydrogen with balance fuel cell inert gases. Upon reach of the equilibrium gas composition, the gas composition of at least 0.0001% hydrogen with balance fuel cell inert gases is maintained during system shutdown. Specifically, during a period after the system shutdown until the next start-up (leaving period), a hydrogen concentration in the fuel cell is monitored and hydrogen is supplied to the fuel cell as needed.