Non-bipolar fuel cell stack configuration

Details Non-bipolar fuel cell stack configuration Non-bipolar fuel cell stack configuration

1998-12-15

2001-02-27

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000

Reexamination Certificate

active

06194095

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to non-bipolar fuel cells and more specifically to high energy fuel cell stacks that deliver from tens of watts to megawatts of power.
The fundamental components of a prior art non-bipolar fuel cell array are shown in the schematic cross-sectional view of FIG.
1
. The basic components are the porous dielectric substrate
1
, the electrolyte
6
, the fuel electrode
2
, the oxidizer electrode
3
, the cell breaks
7
and
16
, the cell interconnects
12
, the external electrical circuit
20
, and the electrical load
9
. The fuel cell operates with the fuel
10
(such as hydrogen or methanol) dissolving in an electrolyte
6
. The dissolved fuel
10
catalytically breaks down into monatomic hydrogen
15
on the catalyzed fuel electrode
2
. The monatomic hydrogen
15
travels through the fuel electrode
2
, giving up an electron
19
to the electrode
2
, and forms a hydrogen ion
17
in the proton conductive electrolyte
5
. The electron
19
travels through the cell interconnects
12
to the adjacent cell oxidizer electrode
3
, which is formed over conduction electrode
4
. The hydrogen ion
17
travels though the conductive electrolyte
5
to the oxidizer electrode
3
. At the negative output terminal
22
of the array, electrons
19
flow though the electrical circuit
20
through an electrical load
9
and to the positive terminal of the array
23
. The array voltage is determined by the number of cells in the array connected in series. Each of the cells are electrically separated from the adjacent cells by dielectric occupied regions called cell breaks
7
and
16
. Adjacent cells are electrically connected by electron conductive vias or cell interconnections
12
. At the oxidizer electrode
3
and
4
, air
8
is catalytically reacted with the surface of the catalytic electrode
3
to form surface oxygen
13
, or oxygen ions
18
in the electrolyte. The oxygen electrode is made of layers of conductive metal films
4
and catalytic electrodes
3
. The oxygen ions
18
then receive the electrons from the electrodes
3
and form water
14
(a by-product) at the oxygen electrode
3
. On the fuel electrode
2
the fuel is gradually catalytically stripped of it's hydrogen
15
to leave carbon monoxide
24
on the surface of the electrode. The carbon monoxide
24
is oxidized to carbon dioxide
11
by taking the oxygen from water
10
in the fuel or by oxygen
25
which is diffused through the fuel enclosure wall
21
. The carbon dioxide
11
by-product diffuses out though the fuel enclosure wall
21
or through the cell break regions
7
and
16
. The water
14
by-product diffuses out from the oxygen electrode
3
to the surroundings. This particular example shows the fuel electrode
2
being pore free. This pore free electrode
2
can block fuel diffusion such as methanol
10
while passing monatomic hydrogen
15
to allow the fuel cell to efficiently utilize the methanol fuel. It may also add diatomic hydrogen diffusion impedance while preferentially having a low impedance to monatomic hydrogen, which has been catalyzed. Thus the pore free electrode
2
can also improve the performance of hydrogen fueled fuel cells.
By utilizing liquid methanol and water fuel, this type fuel cell packs more energy in a smaller space than conventional rechargeable batteries. The methanol fuel has effectively 5 to 13 Whr per cubic inch (20% to 50% efficiency) energy density. This is 3 to 9 times the energy density of today's best nickel cadmium batteries, and 40 to 120 times that of standard cellular phone battery packs. Also, these micro-fuel cells are lighter than conventional rechargeable batteries. The methanol fuel has effectively 1200 to 3000 Whr per kg energy per unit mass (20% to 50% efficiency). This is 2 to 5 times the 600 Whr per kg quoted for the latest rechargeable lithium ion batteries (Science News, Mar. 25, 1995). Various patents, such as U.S. Pat. No. 5,631,099, U.S. Pat. No. 5,759,712, U.S. Pat. No. 5,364,711, and U.S. Pat. No. 5,432,023 describe such non-bipolar fuel cells that run on hydrogen, hydrocarbon fuels, and oxygen. However, they do not describe how to assemble these fuel cells into larger parallel fuel cell stacks, which is the primary objective of this patent.
Our earlier U.S. Pat. Nos. 4,673,624 and 5,631,099 describe how to form non-bipolar stacks on insulator substrates. The method of stacking the fuel cells along a common fuel and electrical power connection is also mentioned in our U.S. Pat. No. 5,759,712. The present invention is intended to extend the micro-fuel cell principles set forth in these earlier patents and to show how these fuel cells are configurable into a stack to provide higher power capacity systems with air flow cooling. The present invention also shows how water is used along with air flow cooling to provide a heat and water exchanger.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to form modular power units that may be connected in parallel to deliver power in large quantity from tens of Watts to megawatts. These larger configurations of micro-fuel cells use active circulation and a variety of compatible reactants to achieve the high power outputs needed in many modern applications. An example of applications that realize a significant advantage from such power systems include, but are not limited to, household and building electrical power generators, portable electrical power generators, large power tools, utility power generators, telecommunications electrical power, and vehicle power. The principal advantages of using a fuel cells in these applications are that (1) the fuel cell realizes roughly twice the efficiency of the conventional heat engines, (2) they are quiet in operation, and (3) they are far less polluting.
The fuel cells of this invention may be formed on plastic sheets which make the manufacturing process suitable for large volume applications. Also, a critical component found in conventional bipolar fuel cell stacks, the electrically conductive separator plate, is completely eliminated in this approach. It is estimated that by eliminating this component from the fuel cell stack, a reduction in cost of from 10% to 20% is realized. As a result, these fuel cells have advantages over conventional fuel cell designs because of reduced mass, fewer components, and lower manufacturing and assembly costs.
This patent covers two embodiments for the packaging techniques of fuel cells for higher power applications. One preferred embodiment is a sealed assembly of multiple parallel arrays. A second preferred embodiment is a modular assembly of multiple parallel arrays. In the sealed assembly, the desired number of arrays are built up and sealed during the manufacturing phase. In the modular approach, the fuel cell arrays are assembled into fuel and air circulation frames to form modules that make connections for fuel, air, and electrical contact with a built-in bus structure. In the modular approach, the bus permits multiple modules to be connected in parallel by the enduser in as few as one module up to a large number of modules, depending on the application. This allows fuel cell energy systems to be sized appropriately to the application by simply adding or removing modules. The fuel cell modules may be installed or removed while the system is running, resulting in minimum down time for maintenance. They may also be adapted to offer a means for self-cleaning the cells, for purging the fuel lines, and for a “fail-safe” power shut down if unfavorable conditions exist.


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patent: 4243508 (1981-01-01), Dankese
patent: 4252868 (1981-02-01), Bohm et al.
patent: 4421579 (1983-12-01), Covitch et al.
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patent: 4666579 (1987-05-01), Beaver et al.
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patent: 4793910 (1988-12-01), Smotkin et al.
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