US Patent 7855022 Fuel system with improved fuel cell shutdown

A fuel cell system having a fuel cell with an anode and a cathode wherein both the cathode and anode each have a flow path with an inflow and outflow. A gaseous source containing oxygen is connected to the inflow of the cathode flow path while a gaseous fuel source is connected to the inflow of the anode flow path. Upon shutdown of the fuel cell, a control system reduces the stoichiometric ratio at the anode to less than or equal to one to thereby deplete the oxygen from the gas at the cathode. A normally closed valve is fluidly connected between the cathode outflow and the anode inflow. The control system opens the valve upon shutdown of the fuel cell to thereby purge the fuel from the anode flow path with the oxygen depleted outflow from the cathode flow path.