Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1997-09-28
2000-04-18
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 26, 429 35, 429 39, H01M 802
Patent
active
060513314
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to fuel cells, and more particularly to fuel cells constructed of stacked platelets having integrated fluid management technology (IFMT), and to methods of manufacture and operation of the IFM cells. A particular embodiment employing the principles of this invention is ahydrogen-air/O.sub.2 fuel cell employing multiple separators formed of bonded platelets of titanium. niobium, copper, stainless steel, aluminum or plastic having individually configured micro-channel reactant gas, coolant and humidification zones therein, which cells operate in the range of about 50 to 150.degree. C., and have an output of on the order of0.25-1.0 kW per Kg and 0.5-1.0 kW/L for use in both stationary and mobile power generation applications in open or closed loop configurations. The IFM platelet and separator design can be adjusted throughout the fuel cell stack to accommodate varying thermal management and humidification requirements within each cell.
BACKGROUND ART
Fuel cells for direct conversion of hydrogen or carbonaceous fuels to electricity have shown great theoretical promise, but have not become widely used in commerce because of technical problems and economic reasons. In the field of hydrogen-air/O.sub.2 fuel cells, power density, that is kilowatts of power generation per pound has been marginal, and the lifetime has been unsatisfactorily short. Prior art cells have experienced dropoff in power with age due in part to poisoning of catalysts or electrolyte membranes, and the poor distribution of fuel gases internally has led to thermal hot spots leading to cell failure and the like.
A particularly important class of fuel cells with promise for stationary and mobile electricity generation is the low temperature H.sub.2 /O.sub.2 fuel cell employing solid polymeric proton exchange membrane having a noble metal catalyst coated on both sides thereof, which membrane is located between the fuel cell electrodes or electrically conductive separators. These fuel cells employ H.sub.2 as fuel, whether directly supplied as such or generated in association with the cell by chemical reaction, such as electrolysis or from metal hydrides. The oxidant is O.sub.2 or air, and water is required both for cooling and for humidification of the membrane to keep it from drying out and becoming inefficient or structurally weakened through cracking. Typically, the anode side dries out first for a variety of reasons, including electrosmotic pumping from anode to cathode, the supply of gases in excess of the electrochemical reaction rate, and the air or oxygen flow on the cathode side purges both the product water and the water vapor passing through the membrane from the hydrogen anode side. Accordingly, the fuel gases are humidified in the fuel cell stack to reduce the dehydration effect The cooling water removes excess heat generated in the slow combustion of the catalyst-mediated electrochemical reaction in the cells, and is conducted external of the stack for heat exchange. In some designs the cooling water is used to humidify the reactant gases.
There are several suitable electrode membrane assemblies (EMAs) available for such low temperature fuel cells. One is from H Power Corp of Bellville, N.J. which employs a Pt catalyst coated on a polymer film, such as duPont NAFION.RTM. brand perflourosulfonated hydrocarbon as the membrane. Alternatively, Dow Chemical provides a perflourosulfonated polymer which has been reported in U.S. Pat. No. 5,316,869 as permitting current densities on the order of 4000 amps/s.f. with cell voltages in excess of 0.5 V/cell, for a cell stack power density in excess of 2 kw/s.f.
A typical design of currently available stacks is the Ballard Fuel Cell Stack of 35 active electrochemical cells 19 thermal management cells, and 14 reactant humidification cells employing a Pt on NAFION 117 EMA in stacks of 1/4" thick graphite plates. The stack is reported to have an overall volume of 0.5 cu. ft with a weight of 94 lbs and a 3 kw output from H.sub.2 and O.sub.2.
However, the grap
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Hodge Rex
Mueggenburg H. Harry
Spear, Jr. Reginald G.
Dulin Jacques M.
H Power Corporation
Kalafut Stephen
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