Sputter-deposited fuel cell membranes and electrodes

Details Sputter-deposited fuel cell membranes and electrodes Sputter-deposited fuel cell membranes and electrodes

1998-09-22

2001-01-09

Bell, Bruce F. (Department: 1741)

Chemistry: electrical current producing apparatus, product, and

Having earth feature

C429S047000, C429S047000, C429S047000, C204S290010, C204S283000, C204S192140, C204S296000

Reexamination Certificate

active

06171721

ABSTRACT:

FIELD
The invention relates to chemical fuel cells. More particularly, the invention relates to sputter-depositing catalysts onto membranes and electrodes.
BACKGROUND
Chemical fuel cells utilize renewable resources and provide an alternative to burning fossil fuels to generate power. Fuel cells utilize the oxidation/reduction potentials of chemical reactions to produce electrical current.
For example, methanol is a known example of a renewable fuel source used in chemical fuel cells. In a methanol driven fuel cell, methanol and water is circulated past an anode that is separated from a cathode by a membrane that is selectively permeable to protons. The following chemical reaction takes place at the anode.
Anode: CH
3
OH+H
2
O→CO
2
+6H
+
+6e
−
The protons generated at the anode pass through the membrane to the cathode side of the fuel cell. The electrons generated at the anode travel to the cathode side of the fuel cell by passing through an external load that connects the anode and cathode. Air or an alternative oxygen source is present at the cathode where the electro-reduction of oxygen occurs resulting in the following chemical reaction.
Cathode: 1.5O
2
+6H
+
+6e
−
→3H
2
O
One of the important aspects of a chemical fuel cell is the membrane-electrode assembly (MEA). The MEA typically includes a selectively permeable polymer electrolyte membrane bonded between two electrodes, e.g., an anode electrode and a cathode electrode. Usually, both the anode and the cathode each contain a catalyst, often a noble metal. Known processes for fabricating high performance MEAs involve painting, spraying, screen-printing and/or hot-bonding catalyst layers onto the electrolyte membrane and/or the electrodes. These known methods can result in catalyst loading on the membrane and electrodes in the range from about 4 mg/cm
2
to about 12 mg/cm
2
. Since noble metals such as platinum and ruthenium are extremely expensive, the catalyst cost can represent a large proportion of a fuel cell's total cost. Therefore, there exists a need for reducing the amount of deposited catalyst, and hence the cost.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method for preparing a membrane for use in a fuel cell membrane electrode assembly that includes the steps of providing an electrolyte membrane, and sputter-depositing a catalyst onto the electrolyte membrane. In one embodiment, the electrolyte membrane further includes at least a first side and a second side wherein the catalyst is applied to the first side and the second side of the electrolyte membrane.
In another embodiment, the sputter-deposited catalyst is sputter-deposited to an anode side, a cathode side, or both the anode and the cathode side of the electrolyte membrane.
The methods for preparing a membrane include depositing ranges of catalyst weights including catalyst weights of less than about 1.0 mg of catalyst per square centimeter of the electrolyte membrane, catalyst weights of less than about 0.05 mg of catalyst per square centimeter of electrolyte membrane, and catalyst weights ranging from about 0.05 mg of catalyst per square centimeter of the electrolyte membrane to about 1.0 mg of catalyst per square centimeter of the electrolyte membrane.
In another embodiment, the catalysts used in the methods for preparing a membrane include the transition metals. Further, the catalysts include mixtures of two or more catalysts, catalyst alloys and/or oxides thereof. The catalysts can be selected from Pt, Ru, Ni, Ti, Zr, Sn, SnO
2
, Os, Ir, W, WO
3
, Pd, Mo, Nb, RuO
2
, and Re.
In another embodiment, the catalysts are sputter-deposited as layers. Two or more catalysts may be sputter-deposited at the same time.
In another embodiment, the electrolyte membrane further includes a first side and a second side wherein the catalyst further includes two or more catalysts, and wherein the two or more catalysts are sputter-deposited to at least one side of the electrolyte membrane.
In a second aspect, the invention provides a method for forming an electrode for use in a fuel cell membrane electrode assembly that includes the steps of obtaining a catalyst, obtaining a backing, and sputter-depositing the catalyst onto the backing. In one embodiment, the backing is carbon paper. In other embodiments, the electrode is an anode or a cathode.
The methods for preparing an electrode include depositing ranges of catalyst weights including catalyst weights of less than about 1.0 mg of catalyst per square centimeter of the backing, catalyst weights of less than about 0.05 mg of catalyst per square centimeter of backing, and catalyst weights ranging from about 0.05 mg of catalyst per square centimeter of the backing to about 1.0 mg of catalyst per square centimeter of the backing.
In another embodiment, the catalysts used in the methods for preparing an electrode include the transition metals. Further, the catalysts include mixtures of two or more catalysts, catalyst alloys and/or oxides thereof. The catalysts can be selected from Pt, Ru, Ni, Ti, Zr, Sn, SnO
2
, Os, Ir, W, WO
3
, Pd, Mo, Nb, RuO
2
, and Re.
In another embodiment, the catalysts are sputter-deposited as layers. Further, two or more catalysts may be sputter-deposited at the same time.
In a third aspect, the invention provides a fuel cell that includes an anode electrode, a cathode electrode, a fuel supply, and an electrolyte membrane, wherein the electrolyte membrane includes a sputter-deposited catalyst, and the sputter-deposited catalyst is effective for sustaining a voltage across a membrane electrode assembly in the fuel cell.
In other embodiments, the catalyst is sputter-deposited to an anode side, a cathode side or both the anode side and the cathode side of the electrolyte membrane.
In another embodiment, the fuel cell has various sputter-deposited catalyst weight ranges including catalyst weights that are less than about 1.0 mg of catalyst per square centimeter of the electrolyte membrane, less than about 0.05 mg of catalyst per square centimeter of the electrolyte membrane, and/or range from about 0.05 mg of catalyst per square centimeter of the electrolyte membrane to about 1.0 mg of catalyst per square centimeter of the electrolyte membrane. In another embodiment, the catalyst weights are found on the anode side of the electrolyte membrane, or the cathode side of the electrolyte membrane, or both the anode side and the cathode side of the electrolyte membrane.
In another embodiment, the catalysts used in the fuel cell include the transition metals. Further, the catalysts include mixtures of two or more catalysts, catalyst alloys and/or oxides thereof. The catalysts can be selected from Pt, Ru, Ni, Ti, Zr, Sn, SnO
2
, Os, Ir, W, WO
3
, Pd, Mo, Nb, RuO
2
, and Re.
In another embodiment, the catalysts are sputter-deposited as layers. Two or more catalysts may be sputter-deposited at the same time.
In another embodiment, the electrolyte membrane of the fuel cell includes a first side and a second side, wherein the catalyst further includes two or more catalysts, and wherein the two or more catalysts are sputter-deposited to at least one side of the electrolyte membrane.
In another embodiment, the fuel cells are fabricated as methanol fuel cells or hydrogen fuel cells.
Unless otherwise defined, all technical and scientific terms and abbreviations used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the present specification, including definitions, will control. Other features and advantages of the invention will be apparent from the following description of the preferred embodiments and from the claims.


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patent: 5750013 (199

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