Abstract: A fuel cell system that employs a technique for reducing or significantly eliminating the MEA degradation that occurs as a result of the hydrogen-air front in the anode flow channels at system start-up. After system shut-down, any hydrogen remaining within the anode flow channels will be quickly reacted or diffused. At the next start-up, a switch is closed to provide a dead short across the positive and negative terminals of the fuel cell stack as hydrogen is being introduced into the anode flow channels. The existing air in the cathode flow channels reacts with the hydrogen being introduced across the membrane in the normal fuel cell reaction. However, the short prevents a voltage potential across the membrane.

Abstract: A fuel cell has a hydrogen flow path adapted to pass hydrogen into communication with an anode catalyst of an MEA. A coolant flow path is adapted to pass coolant through the fuel cell to cool the fuel cell. An enclosure encompasses at least a portion of the hydrogen flow path, the coolant flow path, or both. A hydrogen vent is adapted to vent hydrogen from the enclosure without reliance upon any electrical device. The hydrogen vent can prevent a frame front from passing into the enclosure and can be made of a porous material such as cellulose, plastic (for example, a foamed plastic) or metal (for example a sintered metal). A method of manufacturing a fuel cell includes passively venting hydrogen to maintain a hydrogen concentration level within the enclosure below about 4 percent. Additional enclosures with hydrogen vents may also be provided.

Abstract: A system and method for determining reactant gas flow through a fuel cell stack to determine potential stack problems, such as a possible low performing fuel cell. The method includes applying a perturbation frequency to the fuel cell stack and measuring the stack current and stack voltage in response thereto. The measured voltage and current are used to determine an impedance of the stack fuel cells, which can then be compared to a predetermined fuel cell impedance for normal stack operation. If an abnormal fuel cell impedance is detected, then the fuel cell system can take corrective action that will address the potential problem.

Abstract: A fuel cell system that includes a fuel cell stack providing high voltage power. A tap is electrically coupled to the positive end of the stack to provide a positive voltage output terminal of the fuel cell stack, and a tap is electrically coupled to the negative end of the stack to provide a negative output terminal of the fuel cell stack. A low voltage tap is electrically coupled to one or more intermediate bipolar plates of the stack to provide low voltage power. Several intermediate taps can be electrically coupled to the bipolar plates, where a center intermediate tap is designated a reference potential tap. A switching network switches the several voltage potentials to provide an AC signal.

Abstract: A fuel cell system is provided that includes a fuel cell stack with a plurality of fuel cells and a power converter in electrical communication with the fuel cell stack. The power converter is configured to selectively regulate a power of the fuel cell stack and short circuit the fuel cell stack, as desired. A method for starting the fuel cell stack is also described, including the steps of causing a short circuit of the fuel cell stack by placing the power converter in a short circuit mode; introducing a hydrogen to the anodes of the fuel cell stack to displace a quantity of air on the anodes; and placing the power converter in a power regulation mode. A degradation of the fuel cell stack during start-up is thereby militated against.

Abstract: A technique for heating a fuel cell stack at stack start-up that includes using the vehicle motor drive system to generate waste heat independent from providing traction. Particularly, at fuel cell stack start-up, the electric traction inverter associated with the traction motor that drives the vehicle is controlled so that command signals provided by an inverter to a traction motor do not provide motor torque, but dissipates power into the motor windings and/or motor structure as waste heat. Thus, the output power generated by the fuel cell stack can be made high enough to quickly heat the fuel cell stack through inefficiencies in the stack operation, without providing driving torque. Additionally, the electric traction inverter can be operated so that waste heat is generated within the semiconductor power switches in the inverter.

Abstract: A fuel cell system that employs a technique for reducing or significantly eliminating the MEA degradation that occurs as a result of the hydrogen-air front in the anode flow channels at system start-up. After system shut-down, any hydrogen remaining within the anode flow channels will be quickly reacted or diffused. At the next start-up, a switch is closed to provide a dead short across the positive and negative terminals of the fuel cell stack as hydrogen is being introduced into the anode flow channels. The existing air in the cathode flow channels reacts with the hydrogen being introduced across the membrane in the normal fuel cell reaction. However, the short prevents a voltage potential across the membrane.

Abstract: A fuel cell system that employs a technique for reducing MEA degradation during system shut-down that occurs as a result of the hydrogen and air being present in the fuel cell stack flow channels. The fuel cell system includes a non-linear load element, such as a positive temperature coefficient resistor, electrically coupled to each fuel cell in the fuel cell stack. The non-linear element operates such that it has high electrical conduction at low cell voltages and low electrical conduction at high cell voltages. During system shut-down, the voltage that is generated as a result of the hydrogen and air interaction in the fuel cells that creates a low cell voltage is drawn from the fuel cell and dissipated by the element. During system operation, the fuel cell potentials are relatively high and the resistance of the element goes up so that less current flows through the element, thus reducing electrical losses.

Abstract: A fuel cell system is provided that includes a fuel cell stack with a plurality of fuel cells and a power converter in electrical communication with the fuel cell stack. The power converter is configured to selectively regulate a power of the fuel cell stack and short circuit the fuel cell stack, as desired. A method for starting the fuel cell stack is also described including the steps of causing a short circuit of the fuel cell stack by placing the power converter in a short circuit mode; introducing a hydrogen to the anodes of the fuel cell stack to displace a quantity of air on the anodes; and placing the power converter in a power regulation mode. A degradation of the fuel cell stack during start-up is thereby militated against.

Abstract: A system for providing fuel recirculation in a fuel cell is disclosed, wherein the system uses a cathode exhaust flow to energize a fuel recirculation pump that facilitates the fuel recirculation from an anode exhaust passage to an anode supply passage.

Abstract: A method and apparatus for a high frequency resistance measurement instrument with a reasonable dynamic range, which militates against saturation in the presence of one or more large undesirable signals, the high frequency measurement instrument capable of employing multiple alternating currents of differing frequencies to maintain measurement capability despite signal chain saturation in the presence of a large undesirable signal.

Abstract: A method and apparatus for a high frequency resistance measurement instrument with a reasonable dynamic range, which militates against saturation in the presence of one or more large undesirable signals, the high frequency measurement instrument capable of employing multiple alternating currents of differing frequencies to maintain measurement capability despite signal chain saturation in the presence of a large undesirable signal.

Abstract: A method of addressing one MEA failure mode by controlling MEA catalyst layer overlap, and the apparatus formed thereby is disclosed. The present invention addresses a feature of membrane electrode assembly (MEA) architecture that is associated with field failures due to the loss of ionomer from the edges of the electrolyte. To address ionomer degradation, the present invention provides a MEA design in which the cathode catalyst edges are closer than the anode catalyst edges to the edges of the electrolyte.