Chemistry: electrical current producing apparatus – product – and – Having earth feature
Reexamination Certificate
2001-03-28
2004-02-17
Valentine, Donald R. (Department: 1742)
Chemistry: electrical current producing apparatus, product, and
Having earth feature
C429S006000
Reexamination Certificate
active
06692861
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fuel cell that use carbon and oxygen as fuel sources. In particular, the fuel cell comprises a carbon-containing anode, an electrolyte and a solid state cathode. Heating the fuel cell to temperatures of 400° C.-2000° C. generates an electrical output of at least 1 mW·cm
−2
. The present invention also discloses a method for generating electricity with a fuel cell comprising a carbon-containing anode, an electrolyte and a solid state cathode.
BACKGROUND OF THE INVENTION
The most common commercially available fuel cells use hydrogen and oxygen as fuel gases. Disadvantages of the current systems include the lack of a readily available hydrogen source, the bulky apparatus needed to contain hydrogen and the need for safety precautions for storing an explosive gas such as hydrogen. Such disadvantages can lead to increased costs and can preclude or make difficult the the development of some compact, portable and mobile applications.
Using carbon as a fuel source presents some unique characteristics over current metal/air, dry cell and wet cell batteries. The ratios of valence number to molecular weight, 4:12 and 2:12, are low, providing a potential of producing more electrons per unit atomic weight. Hydrogen is the only element that is more efficient than carbon. Unlike hydrogen, conductive carbon sources, such as coal, are abundant and relatively inexpensive. Carbon materials can be fashioned in any desired shape which allows a compact design for mobile applications. Finally, carbon presents a very low number of safety hazards. Carbon, however is chemically inert under moderate conditions and must be heated to temperatures of at least 400° C. to overcome the activationz energy in a reaction with oxygen. For example, coal and graphite react with air rapidly at 750° C. and 850° C. respectively.
Patents which disclose the use of carbon as an anode include U.S. Pat. No. 460,122 and U.S. Pat. No. 5,589,289. It is believed that none of the fuel cells described in these patents have had widespread commercial success. U.S. Pat. No. 460,122 relates to a process for generating electricity by heating carbon or carbonaceous materials to high temperatures in the presence of an active agent such as a metal oxide or a salt. The carbon and active agent is contained in metal pot which also functions as a cathode. The patent suggests that heating the pot results in a reaction between the oxide and carbon to form carbon monoxide and a resulting electrical current. U.S. Pat. No. 5,589,289 relates to a process for synthesizing a carbon anode. An aromatic organic monomer is subjected to condensation and reduction reactions at high temperatures to yield an amorphous carbon material that displays charge and discharge characteristics. The carbon anode has applications for a rechargeable electrochemical cell.
There remains a need to develop more energy efficient fuel cells that provide a greater electrical output over the commercially available products, allow a more compact design for greater mobility, are easy to construct and are safe to use. Accordingly, an object of the present invention is the provision of a fuel cell that employs a carbon anode as a fuel source and operates with a solid state cathode for use at temperatures between 400° C. and 2000° C. A method and apparatus for generating electricity with a fuel cell apparatus are also disclosed.
SUMMARY OF THE INVENTION
The present invention relates to a fuel cell with carbon and oxygen fuel sources for generating electricity and a method for generating electricity with a carbon-oxygen fuel cell.
One aspect of the invention provides a fuel cell for generating electricity using carbon and oxygen as fuel sources. The fuel cell comprises a carbon-containing anode, an electrolyte in contact with the anode at a first contact surface area and a solid state cathode in contact with the electrolyte at a second contact surface area. The cathode reduces oxygen, O
2
, to oxygen anions, O
2−
, and the electrolyte allows passage of oxygen anions to the anode. The fuel cell is operable at a temperature of between 400° C. and 2000° C. and generates an electrical output of at least 1 mW·cm
−
2
of the second contact surface area.
The carbon-containing anode used preferably has a resistivity of between about 10
−5
ohm-cm to about 100 ohm-cm. The anode is solid or in particle form and is preferably selected from the group consisting of graphite, quasi-graphite, coal, coke, charcoal, fullerene, buckminsterfullerene, carbon black, activated carbon, decolorizing carbon and mixtures thereof.
The invention preferably provides a solid state electrolyte having a distance therethru from a first contact surface area adjacent to an anode to a second contact surface area adjacent to a cathode of between about 1 &mgr;m and 1000 &mgr;m, preferably between about 1 &mgr;m and 600 &mgr;m and more preferably between about 1 &mgr;m and 100 &mgr;m. Where the electrolyte is a solid layer, the distance is preferably between about 1 &mgr;m and about 1000 &mgr;m, preferably between about 1 &mgr;m and 600 &mgr;m and more preferably between about 1 &mgr;m and 100 &mgr;m. The electrolyte most preferably has a formula (ZrO
2
)(HfO
2
)
a
(TiO
2
)
b
(Al
2
O
3
)
c
(Y
2
O
3
)
d
(M
x
O
y
)
e
where a is from 0 to about 0.2, b is from 0 to about 0.5, c is from 0 to about 0.5, d is from 0 to about 0.5, x is an integer greater than 0 and less than or equal to 2, y is an integer greater than 0 and less than or equal to 3, e is from 0 to about 0.15, and M is selected from the group consisting of manganese, iron, cobalt, nickel, copper and zinc.
The electrolyte preferably has a melting temperature of between about 300° C. and about 2000° C. The electrolyte can be selected from the group consisting of a metal carbonate, a metal oxide, a plurality of metal carbonates, a plurality of metal oxides and mixtures thereof.
The solid state cathode of this invention preferably has an oxygen ionization rate of between about 10
−8
g·s
−1
·cm
−2
and about 10
−3
g·s
−1
·cm
−2
. The cathode also has an electrical resistivity of between about 10
−9
ohm-cm to about 100 ohm-cm. The cathode is preferably selected from the group consisting of a metal, a metal oxide, a plurality of metal oxides and mixtures thereof. The solid state cathode preferably has a formula La
x
Mn
y
A
a
B
b
C
c
O
d
where A is an alkaline earth metal, B is selected from the group consisting of scandium, yttrium and a lanthanide metal, C is selected from the group consisting of titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, zirconium, hafnium, aluminum and antimony, x is from 0 to about 1.05, y is from 0 to about 1, a is from 0 to about 0.5, b is from 0 to about 0.5, c is from 0 to about 0.5 and d is between about 1 and about 5 so that an oxide is always present, and at least one of x, y, a, b and c is greater than zero. The solid state cathode may also have a formula Li
x
M
1-x
O where M is a metal selected from the group consisting of nickel and cobalt and x is from 0 to about 0.25.
In another aspect of the invention, a method is provided for generating electricity in a fuel cell having a carbon-containing anode. The method comprises the steps of providing a carbon-containing anode, an electrolyte in contact with the carbon-containing anode at a first contact surface area and a solid state cathode in contact with the electrolyte at a second contact surface area. An oxygen-containing gas flow is directed to the cathode and the fuel cell is heated to a temperature of between about 400° C. and about 2000° C. to produce an electrical output of at least about 1 mW·cm
−2
of the second contact surface area.
Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, which are schematic and which are not intended to be drawn to scale. In the figures, each identica
CellTech Power, Inc.
Valentine Donald R.
Wolf Greenfield & Sacks P.C.
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