Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2002-09-23
2004-05-25
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S010000, C429S006000
Reexamination Certificate
active
06740440
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to liquid cooled fuel cells and, more particularly, to a fuel cell, a fuel cell system, and methods for cooling a fuel cell or fuel cell system.
SUMMARY OF THE INVENTION
Fuel cells rely on hydrogen oxidation and oxygen reduction to produce electrical energy. The byproduct of these catalytic reactions is water. Thermodynamically, the oxidation of hydrogen fuel at an anode and the reduction of oxygen at a cathode, both the anode and the cathode located within a fuel cell, should give a cell potential of about 1.23 V. However , the actual measured value is typically around 1 V. This difference in cell voltage is due primarily to the slow kinetics of the cathode, which amounts to an almost 200 mV loss in cell voltage. The result of this loss in cell voltage is an expression of excess heat within the fuel cell. The removal of such excess heat is essential to increasing the useful lifetime of the fuel cell components.
As multiple fuel cells are arranged in a stack to increase electrical output, heat generation becomes significantly high. Consequently, in order to remove such excess heat, a coolant is employed that has a high heat capacity and which is physically stable at a temperature between about −40° C. and about 140° C. Aqueous coolants used with conventional combustion engine vehicles fall within this range and typically comprise a mixture of ethylene glycol and water. However, the design of today's fuel cell stacks requires that the coolant be non-conducting (dielectric). If the coolant has a significant conductivity, it will lead to a variety of conductive coolant-induced stack problems including shunt currents that reduce fuel efficiency, gas evolution (O
2
and H
2
) in the header area creating increased pressure within the fuel cell stack requiring venting, coolant degradation, and oxygen degradation of stack components including coating blistering and corrosion acceleration.
Known in the art is the use of ion exchange resins with deionized water to rid of impurities in the coolant and maintain its low conductivity. However, the use of deionized water is limited in areas that experience severe winter weather where temperatures can reach −40° C. At this temperature, water freezes and would not be a suitable coolant or the stack.
Also known is the use of a pure dielectric coolant (i.e., Therminol®-D available from Solutia Inc., St. Louis, Mo.). As a pure dielectric, the fluid does not allow current to flow through the header area of the stack. However, the cost as well as the incompatibility of the coolant with gaskets currently employed in fuel cell stacks makes the use of such pure dielectric coolants impractical.
Accordingly, the present inventors have recognized a need for improvements in liquid coolant technology for fuel cell stacks.
The present invention meets the above-mentioned need by providing an inexpensive and readily available dielectric coolant for fuel cell stacks. Although the present invention is not limited to specific advantages or functionality, it is noted that because the coolant is a dielectric and does not allow for any ionic transport, it does not affect the stack components, and does not allow for any performance loss caused by shunt currents on the header area of the stack. Consequently, corrosion inhibitors need not be added to prohibit O
2
degradation of fuel cell components. Although the heat capacity of the dielectric coolant of the present invention is slightly less than aqueous-based coolants, the present coolant has a low kinematic viscosity which enables it to be pumped at higher flow rates to remove waste heat without an appreciable increase in parasitic pumping power. Moreover, the relatively high boiling point of the dielectric coolant enables operating the fuel cell stack and coolant loop at higher temperatures (~140° C.), increasing the capacity to exhaust heat from the radiator to the environment.
In one embodiment, the present invention provides a fuel cell configured to react fuel with oxygen to generate an electric current and at least one reaction product. The fuel cell comprises an anode flowpath, an anode, a cathode flowpath, a cathode, a membrane disposed between the anode and the cathode, and at least one coolant flowpath. The al ode flowpath is configured to route the fuel through at least a portion of the fuel cell. The anode is in fluid communication with the anode flowpath and upon which a catalytic reaction with the fuel is configured to take place. The cathode flowpath is configured to route the oxygen through at least a portion of the fuel cell. The cathode is in fluid communication with the cathode flowpath and upon which a catalytic reaction with the oxygen is configured to take place. The membrane is disposed between the anode and the cathode such that electrolyte communication is established therebetween during operation of the fuel cell. The coolant flowpath is fluidly decoupled from the anode flowpath and the cathode flowpath. The coolant flowpath defines a coolant isolation manifold that includes a fluid dielectric coolant, which comprises a kerosenic hydrocarbon.
In another embodiment, the present invention provides a fuel cell configured to react fuel with oxygen to generate an electric current and at least one reaction product. The fuel cell comprises an anode flowpath, an anode, a cathode flowpath, a cathode, a membrane disposed between the anode and the cathode, at least one coolant flowpath, and a recirculation assembly. The anode flowpath is configured to route the fuel through at least a portion of the fuel cell. The anode is in fluid communication with the anode flowpath and upon which a catalytic reaction with the fuel is configured to take place. The cathode flowpath is configured to route the oxygen through at least a portion of the fuel cell. The cathode is in fluid communication with the cathode flowpath and upon which a catalytic reaction with the oxygen is configured to take place. The membrane is disposed between the anode and the cathode such that electrolyte communication is established therebetween during operation of the fuel cell. The coolant flowpath is fluidly decoupled from the anode flowpath and the cathode flowpath. The coolant flowpath defines a coolant isolation manifold that includes an inlet, an outlet, and a fluid dielectric coolant, which comprises a kerosenic hydrocarbon. The recirculation assembly comprises a recirculation flowpath, a pump, and a radiator. The recirculation flowpath fluidly connects the coolant isolation manifold inlet and the coolant isolation manifold outlet.
In still another embodiment, the present invention provides a fuel cell system comprising a fuel cell stack comprising a plurality of fuel cells, wherein each fuel cell is configured to react fuel with oxygen to generate an electric current and at least one reaction product. Each fuel cell comprises an anode flowpath, an anode, a cathode flowpath, a cathode, a membrane disposed between the anode and the cathode, and at least one coolant flowpath. The anode flowpath is configured to route the fuel through at least a portion of each fuel cell. The anode is in fluid communication with the anode flowpath and upon which a catalytic reaction with the fuel is configured to take place. The cathode flowpath is configured to route the oxygen through at least a portion of each fuel cell. The cathode is in fluid communication with the cathode flowpath and upon which a catalytic reaction with the oxygen is configured to take place. The membrane is disposed between the anode and the cathode such that electrolyte communication is established therebetween during operation of each fuel cell. The coolant flowpath is fluidly decoupled from the anode flowpath and the cathode flowpath. The coolant flowpath defines a coolant isolation manifold that includes a fluid dielectric coolant, which comprises a kerosenic hydrocarbon.
In yet another embodiment, the present invention provides a fuel cell system comprising a fuel cell stack comprising
Abd Elhamid Mahmoud H
Blunk Richard H.
Lisi Daniel John
Mikhail Youssef Morcos
Brooks Cary W.
General Motors Corporation
Kalafut Stephen
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