Abstract: Liquid cooled systems having coolant circulation loops must often operate in below freezing conditions. For instance, in various applications certain fuel cell systems must be able to tolerate repeated shutdown and storage in below freezing conditions. Conventional glycol-based coolants typically used for internal combustion engines are generally unsuitable for use in the associated fuel cell cooling subsystems due to the presence of additives and/or inhibitors which are normally included to deal with problems relating to decomposition of the glycol. With additives or inhibitors present, the coolant conductivity can be sufficiently high as to result in electrical shorting or corrosion problems. However, provided the purity of the coolant is maintained, a pure glycol and water coolant mixture may be used as a fuel cell system coolant to obtain suitable antifreeze protection. Adequate purity can be maintained by including an ion exchange resin unit in the cooling subsystem.

Abstract: Improved water distribution can be obtained within the cells of a fuel cell series stack by maintaining a suitable temperature difference between the cathode and anode sides of each cell in the stack during shutdown.

Abstract: An electrochemical fuel cell stack with integrated anode exhaust valves is disclosed, comprising a plurality of fuel cells, each fuel cell having an anode and at least one anode flow field channel, an anode exhaust manifold fluidly connected to the at least one anode flow field channel of each fuel cell, and a means for minimizing fluid backflow from the anode exhaust manifold into the anode flow field channels of the fuel cells. Methods for purging, and reducing fuel cell voltage variations within, the electrochemical fuel cell stack are also disclosed.

Abstract: A fuel cell system for powering a work load includes a fuel cell stack and a shunt regulator having a threshold detection; transistorized power switching element, and a dump load. The threshold detection element identifies when an abnormally high voltage rises. The power switching element routes power from the high voltage buss to the dump load. The dump load acts as an electrical energy sink, and may provide dissipated energy to the fuel cell stack in the form of heat. The switching element can also shunt power to the dump load when a digital control signal is set, for example at startup or during cold start conditions.

Abstract: A fuel cell system for powering a work load includes a fuel cell stack and a shunt regulator having a threshold detection; transistorized power switching element, and a dump load. The threshold detection element identifies when an abnormally high voltage rises. The power switching element routes power from the high voltage buss to the dump load. The dump load acts as an electrical energy sink, and may provide dissipated energy to the fuel cell stack in the form of heat. The switching element can also shunt power to the dump load when a digital control signal is set, for example at startup or during cold start conditions.

Abstract: In a hydrogen gas line where the composition of the gas is primarily hydrogen, impurities present in the gas line will typically reduce the speed of sound. Accordingly, an acoustic sensor can be used in such a hydrogen gas line to indicate when impurities have accumulated in the gas line. In particular, the hydrogen gas line may be in a fuel line for an electrochemical fuel cell system. The sensor may comprise transducers, more particularly piezoelectric transducers, as both sound detectors and/or sound generators. Further, the sensor can measure either the speed or frequency of sound to determine the hydrogen concentration. If the fuel is recirculated back to the anode inlet, such a hydrogen sensor in the anode exhaust may be used to determine when it is beneficial to purge the anode exhaust to the external atmosphere.

Abstract: A method for embossing expanded graphite sheet material comprises removing at least a portion of the gas from within the material by exposing the material to a pressure less than atmospheric pressure, and then embossing the material. The pressure to which the material is exposed is preferably no greater than about 400 torr. An apparatus for embossing expanded graphite sheet material at a pressure less than atmospheric pressure comprises: an embossing device, a compression device adapted to urge the embossing device against the material, an embossing chamber comprising the at least one embossing device and adapted to receive the material and to be substantially gas-tight at least when the embossing device is urged against the material by the pressing device, and an evacuation device for reducing the pressure within the embossing chamber.

Abstract: An improved method for embossing expanded graphite sheet material including removing at least a portion of the gas from within the material by exposing the material to a pressure less than atmospheric pressure, and then embossing the material.

Abstract: Certain fuel cells (e.g., solid polymer electrolyte fuel cells) may temporarily exhibit below normal performance after initial manufacture or after prolonged storage. While normal performance levels may be obtained after operating such fuel cells for a suitable time period, this process can take of order of days to fully complete. However, various conditioning and/or maintenance techniques are disclosed that provide for normal performance levels without the need for a lengthy initial operating period.

Abstract: A fuel cell system for powering a work load includes a fuel cell stack and a shunt regulator having a threshold detection; transistorized power switching element, and a dump load. The threshold detection element identifies when an abnormally high voltage rises. The power switching element routes power from the high voltage buss to the dump load. The dump load acts as an electrical energy sink, and may provide dissipated energy to the fuel cell stack in the form of heat. The switching element can also shunt power to the dump load when a digital control signal is set, for example at startup or during cold start conditions.

Abstract: A method of embossing expanded graphite sheet material comprises embossing the material in an embossing atmosphere at a reduced pressure less than atmospheric pressure and maintaining a reduced pressure at least during the embossing step. Preferably, the pressure of the embossing atmosphere is less than or equal to about 400 torr. The embossing atmosphere may comprise an inert gas, such as nitrogen, helium and argon, for example.

Abstract: An improved embossing expanded graphite sheet material comprises removing at least a portion of the gas from within the material by exposing the material to a pressure less than atmospheric pressure, and then embossing the material. Preferably, the pressure to which the material is exposed is less than or equal to about 400 torr. An improved apparatus for embossing expanded graphite sheet material at a pressure less than atmospheric pressure comprises: at least one embossing device; at least one compression device adapted to urge the embossing device against the material; an embossing chamber comprising the at least one embossing device and adapted to receive the material, and to be substantially gas-tight at least when the embossing device is urged against the material by the pressing device; and an evacuation device for reducing the pressure within the embossing chamber. The atmosphere within the embossing chamber may comprise an inert gas, such as, for example, nitrogen, helium and argon.