Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Making catalytic electrode – process only
Reexamination Certificate
2000-12-22
2002-11-19
Bell, Bruce F. (Department: 1741)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Making catalytic electrode, process only
C502S305000, C502S309000, C502S311000, C502S314000, C502S353000, C429S047000, C429S047000, C427S126300, C427S250000, C427S255360, C427S255700, C427S419200, C204S192110, C204S192120, C204S192380, C219S121600
Reexamination Certificate
active
06482763
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fuel cell electrode catalysts comprising alternating platinum-containing layers and layers containing suboxides of a second metal that display an early onset of CO oxidation. Preferably the early onset is manifest as a pre-peak, in addition to the normal Pt CO oxidation peak, in CO oxidation cyclic voltametry. Methods of manufacturing the subject catalysts are also provided. The fuel cell catalysts of the present invention show improved reformate tolerance, and in particular improved CO tolerance.
BACKGROUND OF THE INVENTION
The fuel stream feeding a hydrogen fuel cell may be supplied by reformation of hydrocarbons. However, the reformate stream will typically contain constituents including CO, CO
2
, N
2
and CH
3
in addition to hydrogen. Typical fuel cell catalysts are susceptible to carbon monoxide poisoning, which causes significant loss of power and durability. U.S. Pat No. 4,910,099 discloses one method of improving CO tolerance in fuel cells. In this method, O
2
or air is “bled” to the anode side of the cell, where it reacts with any CO present in the fuel gas stream to form CO
2
. However, this method reduces cell efficiency.
U.S. Pat. No. 5,183,713 concerns a fuel cell catalyst with improved CO tolerance comprised of platinum alloyed with 2-10% tantalum. The metals are not alternately layered and suboxides are not taught.
U.S. Pat. No. 5,523,177 concerns a direct-methanol fuel cell including a partially reduced metal oxide anode porous electrode having an oxide content of between 5 wt % and 20 wt %. The exemplary catalyst is composed of an alloy of platinum and ruthenium. This reference does not teach an alternately layered catalyst. The reference indicates that “partial reduction” proceeds by reduction of PtO
x
, without significant reduction of RuO
x
. (U.S. Pat. No. 5,523,177 at col. 4, ln. 62-col. 5, ln. 4). In addition, the reference teaches that reduction of RuO
x
is not desirable. (Id.) The reference does not teach that the catalyst disclosed therein has any favorable CO tolerance characteristics in a hydrogen/air or reformate/air fuel cell.
U.S. Pat. No. 6,040,077 concerns an alternately layered catalyst of Pt and Ru, including Pt and Ru oxides and suboxides.
A seminal review of anode catalyst materials for CO oxidation (Ross, “The Science of Electrocatalysis on Biometallic Surfaces”, Lawerence Berkeley National Laboratories Report, LBNL-40486) cites the following important criteria for the selection of catalyst materials: the material has to be a Pt alloy, the material alloyed to Pt must not be an oxide or readily form an oxide.
SUMMARY OF THE INVENTION
Briefly, the present invention provides fuel cell electrode catalysts comprising alternating platinum-containing layers and layers containing suboxides of a second metal, where the catalyst demonstrates an early onset of CO oxidation. Preferably the early onset appears as a shoulder in CO oxidation cyclic voltametry and more preferably as a pre-peak.
In another aspect, the present invention provides fuel cell electrode catalysts comprising alternating platinum-containing layers and layers containing suboxides of a second metal selected from the group consisting of Group IIIb metals, Group IVb metals, Group Vb metals, Group VIb metals and Group VIIb metals. Preferably the second metal is selected from the group consisting of Ti, Ta, W and Mo.
In another aspect, the present invention provides methods of making such catalysts. In particular, the present invention provides methods of making such catalysts by alternate deposition of platinum and second metals in the presence of substoichiometric amounts of gaseous oxygen.
What has not been described in the art, and is provided by the present invention, is a CO tolerant fuel cell catalyst of the present composition or the method of it's manufacture provided herein.
In this application:
“suboxide ” means a composition MO
x
of a metal M having one or more chemical oxidation states MO
n
where n is one or more positive rational numbers (typically a ratio of small positive integers), wherein x is not equal to any n and wherein x is less than the greatest n; and
“substituted” means substituted by conventional substituents which do not interfere with the desired product, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc.
“peak” means a local maximum value;
a “pre-peak”, means, in regard to CO oxidation cyclic voltametry, a peak in addition to and appearing at a lower potential than a Pt CO oxidation peak;
“shoulder” means a local maximum in the first derivative of a value;
“early onset of CO oxidation” means CO oxidation occurring at a potential lower than that of the Pt CO oxidation peak. The Pt CO oxidation peak typically occurs at around 400 mV, referenced to a saturated calomel electrode, but may be shifted as low as 200 mV by the presence of other metals, e.g. Ru. Early onset of CO oxidation may be demonstrated by CO oxidation cyclic voltametry, where it is indicated by a rise in current reflecting the oxidation of CO. Preferable conditions for performing cyclic voltametry are 80° C. temperature, ambient pressure and 25 mV/sec scan rate. More specifically, early onset may be demonstrated by comparison of the subject CO oxidation cyclic voltametry curve to a curve obtained for a Pt catalyst. The y-axis of the subject curve (representing electrical current) is normalized to the Pt curve by multiplying the values of the subject curve by a scaling factor such that the two curves have the same value at the Pt oxide reduction peak (label (1) in FIG.
3
). The curves are not normalized in the x-axis (representing electrical potential). “Early onset” is defined with regard to the region of the subject curve between the point of H
2
evolution and a point 140 millivolts more positive than the reference electrode (saturated calomel electrode (SCE)), preferably in the region between H
2
evolution and 110 millivolts above SCE, more preferably in the region between H
2
evolution and 80 millivolts above SCE, and most preferably in the region between H
2
evolution and 50 millivolts above SCE. “Early onset” is seen where a point in that region of the subject curve has a positive slope or, more preferably, demonstrates at least 10% greater capacitive (double layer) current than the Pt curve.
It is an advantage of the present invention to provide fuel cell catalysts demonstrating improved CO tolerance.
REFERENCES:
patent: 4127468 (1978-11-01), Alfenaar et al.
patent: 4812352 (1989-03-01), Debe
patent: 4910099 (1990-03-01), Gottesfeld
patent: 5039561 (1991-08-01), Debe
patent: 5183713 (1993-02-01), Kunz
patent: 5338430 (1994-08-01), Parsonage et al.
patent: 5523177 (1996-06-01), Kosek et al.
patent: 5876867 (1999-03-01), Itoh et al.
patent: 5879827 (1999-03-01), Debe et al.
patent: 5879828 (1999-03-01), Debe et al.
patent: 5916702 (1999-06-01), Marucchi-soos et al.
patent: 5922488 (1999-07-01), Marucchi-soos et al.
patent: 6007934 (1999-12-01), Auer et al.
patent: 6040077 (2000-03-01), Debe et al.
patent: 6146782 (2000-11-01), Wendt et al.
patent: 6165636 (2000-12-01), Giallombardo et al.
patent: 6297185 (2001-10-01), Thompson et al.
patent: 6370834 (2002-04-01), Giallombardo et al.
patent: WO 00/35037 (2000-06-01), None
Ross, “The Science of Electrocatalysis on Biometallic Surfaces”, Lawrence Berkely National Laboratories Report, LBNL-40486.
P. K. Shen and A. C. C. Tseung; “Anodic Oxidation of Methanol on Pt/WO3in Acidic Media”,Journal of Electrochemical Society,vol. 141, No. 11, Nov. 1994, pp. 3082-3090.
A. Ma,Y. Leng, A. Huangh, X. Liao, and Y. Shi; “Performance of a New Electrocatalyst For PEMFC”;Extended Abstracts of the Third International Symposium on New Materials For Electrochemical Systems,Jul. 1999, pp. 80-81. XP-002168085.
G. Lalande, M.C. Denis, P. Gouérec, D. Guay, J. P. Dodelet, and R. Schulz; “Pt-Based Nanocomposites Produced By High Energy Ball Milling As Electrocatalysts In Polymer Electrolyte Fuel Cells”,Journal of New Materials For Electrochemical Systems,vol.
Debe Mark K.
Haugen Gregory M.
Lewinski Krzysztof A.
Thomas, III John H.
Vernstrom George D.
3M Innovative Properties Company
Bell Bruce F.
Dahl Philip Y.
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