Fuel cell technology is a relatively recent development in the automotive industry. It has been found that fuel cell power plants are capable of achieving efficiencies over 55%. Furthermore, fuel cell power plants emit only heat and water as by-products.
Fuel cells include three components: a cathode, an anode and an electrolyte which is sandwiched between the cathode and the anode and permits the transmission of protons from the anode to the cathode. Each electrode contains a catalyst. In operation, the catalyst on the anode splits hydrogen into electrons and protons. The electrons are distributed as electric current from the anode, transmitted externally through some work-related device, such as a drive motor, and then to the cathode. The protons migrate from the anode, through the electrolyte to the cathode. The catalyst on the cathode combines the protons with electrons returning from the work-related device and oxygen from the air to form water. A fuel cell stack is a collection of individual fuel cells stacked together in series.
During operation of the fuel cell stack, a steady flow of hydrogen gas is introduced into the anode side of the fuel cell stack, and a steady flow of air is introduced into the cathode side of the fuel cell stack. Upon shutdown of the fuel cell stack, flow of hydrogen into the anode side of the fuel cell stack is terminated. If hydrogen remains in the fuel cell stack after shutdown, air leaking into the anode could cause the formation of a localized corrosion cell. The cathode potential with respect to a standard hydrogen electrode can reach 1.2-1.5 V. Over time, the high voltage will result in the loss of the carbon substrate supporting the catalyst in the cathode. A loss of substrate and catalyst area will reduce operating voltage, and ultimately limit stack life. This problem is described in patent US 2004/0081866A1 (Bekkedahl et al.)