Fabrication of a membrane having catalyst for a fuel cell

Details Fabrication of a membrane having catalyst for a fuel cell Fabrication of a membrane having catalyst for a fuel cell

1999-05-04

2002-05-21

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Having earth feature

C502S101000

Reexamination Certificate

active

06391486

ABSTRACT:

ORIGIN OF THE INVENTION
The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Public Law 96-517(35 U.S.C. 202) in which the Contractor has elected to retain title.
FIELD OF THE INVENTION
The present invention relates to fuel cells for generating energy by electrochemical reactions, and more specifically to a direct-feed oxidation fuel cell and manufacturing thereof.
BACKGROUND AND SUMMARY OF THE INVENTION
Organic fuels can be used to generate electrical power by converting energy released from electrochemical reactions of the fuels. Organic fuels, such as methanol, are renewable. Typical products from the electrochemical reactions are mostly carbon dioxide and water. These products are environmentally safe. Therefore, organic fuel cells are considered as an alternative energy source to non-renewable fossil fuels for many applications. In addition, use of fuel cells can eliminate many adverse environmental consequences associated with burning of fossil fuels, for example, air pollution caused by exhaust from gasoline-powered internal combustion engines.
Direct liquid-feed oxidation fuel cells are of particular interest due to a number of advantages over other fuel cell configurations. For example, the organic fuel is directly fed in to the fuel cell. This eliminates the necessity of having a chemical pre-processing stage. Also, bulky accessories for vaporization and humidification in gas-feed fuel cells are eliminated. Thus, direct liquid-feed cells generally have simple cell construction and are suitable for many applications requiring portable power supply.
Conventional direct liquid-feed cells usually use a liquid mixture of an organic fuel and an acid/alkali electrolyte liquid, which is circulated past the anode of the fuel cell. Problems associated with such a conventional direct liquid-feed cell are well recognized in the art. For example, corrosion of cell components caused by the acid/alkali electrolyte places significant constraints on the materials that can be used for the cell; fuel catalysts often exhibit poor activity due to adsorption of anions created by the acid electrolyte; and the use of sulfuric acid electrolyte in multi-cell stacks can result in parasitic shunt currents. As a result, the performance of the conventional cells is limited to about less than 0.3 volt in output voltage and less than about 30 mA/cm
2
in output current. In addition, a number of safety issues arise with the use of acidic and alkaline solutions.
NASA's Jet Propulsion Laboratory (JPL) developed an improved direct liquid-feed cell using a solid-state membrane electrolyte. One of the advantages of the JPL fuel cell is the elimination of the liquid acidic and alkaline electrolyte by the membrane electrolyte. This solves many problems in the conventional fuel cells. A detailed description of JPL's fuel cell can be found, for example, in U.S. Pat. No. 5,599,638 and in U.S. patent application Ser. No. 08/569,452, filed on May 28, 1996, both of which are incorporated herein by reference.
FIG. 1
shows a typical structure
100
of a JPL fuel cell with a membrane electrolyte
110
enclosed in housing
102
. The electrolyte membrane
110
is operable to conduct protons and exchange cations. An anode
120
is formed on a first surface of the membrane
110
with a first catalyst for electro-oxidation and a cathode
130
is formed on a second surface thereof opposing the first surface with a second catalyst for electro-reduction. An electrical load
140
is connected to the anode
120
and cathode
130
for electrical power output.
The membrane
110
divides the fuel cell
100
into a first section
122
on the side of the anode
120
and a second section
132
on the side of the cathode
130
. A feeding port
124
in the first section
122
is connected to a fuel feed system
126
. A gas outlet
127
is deployed in the first section
122
to release gas therein and a liquid outlet
128
leads to a fuel re-circulation system
129
to recycle the fuel back to the fuel feed system
126
. In the second section
132
of the cell
100
, an air or oxygen supply
136
(e.g., an air compressor) supplies oxygen to the cathode
130
through a gas feed port
134
. Water and used air/oxygen are expelled from the cell through an output port
138
.
In operation, a mixture of an organic fuel (e.g., methanol) and water is fed into the first section
122
of the cell
100
while oxygen gas is fed into the second section
132
. Electrochemical reactions happen simultaneously at both the anode
120
and the cathode
130
, thus generating electrical power. For example, when methanol is used as the fuel, the electro-oxidation of methanol at the anode
120
can be represented by
CH
3
OH+H
2
O→CO
2
+6H
+
+6e
−
.
and the electro-reduction of oxygen at the cathode
130
can be represented by
O
2
+4H
+
+4e
−
→2H
2
O.
Thus, the protons generated at the anode
120
traverse the membrane
110
to the cathode
130
and are consumed by the reduction reaction therein while the electrons generated at anode
120
migrate to the cathode
130
through the electrical load
140
. This generates an electrical current from the cathode
130
to the anode
120
. The overall cell reaction is:
 2CH
3
OH+3O
2
→2CO
2
+4H
2
O+Electrical Energy.
The inventors recognized the advantages and potential of the JPL's membrane fuel cell. Importantly, the inventors have discovered a number of new materials for various components and processing methods that can be used to improve the performance of this type of fuel cells.
One aspect of the present invention describes new material compositions for catalysts with improved efficiency and methods for forming catalyst layers on the membrane electrolyte including transfer of catalyst decals and deposition of catalyst materials onto a backing layer with minimized catalyst permeation.
Another aspect directs to improve catalyst efficiency and reactivity by increasing the surface area thereof.
Yet another aspect is to increase the reactivity of a catalyst by changing the electronic properties of a catalyst layer.
Still another aspect of the invention is construction and processing of the electrolyte membrane to improve coating, bonding, and to reduce fuel crossover.


REFERENCES:
patent: 3013098 (1961-12-01), Hunger et al.
patent: 3143440 (1964-08-01), Hunger et al.
patent: 4390603 (1983-06-01), Kawana et al.
patent: 5316871 (1994-05-01), Swathirajan et al.
patent: 5330626 (1994-07-01), Banerjee
patent: 5399184 (1995-03-01), Harada
patent: 5599638 (1997-02-01), Surampudi et al.
patent: 59-209277 (1984-11-01), None
patent: 60-165062 (1985-08-01), None
Hamnett et al., Electrocatalysis and the Direct Methanol Fuel Cell, Chemistry & Industry, pp. 480-483 (Jul. 6, 1992).*
Masaji et al., Ordinary Temperature Type Acid Methanol Fuel Cell, Japanese Abstract, JP63076264, (Aug. 22, 1998).*
Zawodzinski et al., Methanol Cross-Over in UMFC's: Development of Strategies for Minimization, Abstract, (Oct. 1994).*
Narayanan et al., Studies on the Electro-Oxidation of Methanol and Formaldehydge at Carbon-Supported Platinum and Platinum Alloy Electrodes, Abstract (Oct. 1992).*
Kosek et al., A Direct Methanol Oxidation Fuel Cell, Abstract (Aug. 8, 1993).*
Nobuyuki et al., Alcoholic Fuel Battery and Operating Method Thereof, Abstract, JP2148657, (Jun. 7, 1990).*
Narayanan et al., Implications of Fuel Crossover in Direct Methanol Fuel Cells, Abstract (Oct. 1993).

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