Direct hydrocarbon fuel cells

Details Direct hydrocarbon fuel cells Direct hydrocarbon fuel cells

1999-11-16

2001-04-10

Bell, Bruce F. (Department: 1741)

Chemistry: electrical current producing apparatus, product, and

Having magnetic field feature

C429S006000, C429S006000, C429S047000, C429S047000, C429S047000, C204S291000

Reexamination Certificate

active

06214485

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to direct use of hydrocarbons in fuel cells and, more particularly, methods, fuel cells and components thereof relating to such use.
BACKGROUND OF INVENTION
Fuel cells are promising electrical power generation technologies, with key advantages including high efficiency and low pollution. Most potential near-term applications of fuel cells require the use of hydrocarbon fuels such as methane, for which a supply infrastructure is currently available. However, fuel cells typically operate only with hydrogen as the fuel. Thus, current demonstration power plants and planned fuel-cell electric vehicles must include a hydrocarbon fuel reformer to convert the hydrocarbon fuel to hydrogen. Fuel cells that could operate directly on hydrocarbon fuels would eliminate the need for a fuel reformer, providing considerable system and economic advantages and presumably improving the viability of the technology.
Prior art fuel cells utilizing hydrocarbon fuels directly have encountered significant problems. For example, direct-methanol polymer electrolyte fuel cells produce relatively low power densities and require prohibitively large Pt loading of the anodes. In addition, methanol can permeate the electrolyte. See, for instance, Ren, X., Wilson, M. S. and Gottesfeld, S. High performance direct methanol polymer electrolyte fuel cells.
J. Electrochem. Soc
., 143, L12-L14 (1996); and Wang, J., Wasmus. S. and Savinell, R. F. Evaluation of ethanol,
1
-propanol, and 2-propanol in a direct oxidation polymer-electrolyte fuel cell a real-time mass spectrometry study.
J. Electrochem. Soc
., 142, 4218-4224 (1995). Furthermore, only alcohol fuels appear feasible with this approach.
Alternatively, prior art solid oxide fuel cells (SOFCs) can utilize hydrocarbons directly via internal or external reforming. In this approach, a hydrocarbon fuel (e.g., methane) is combined with H
2
O and/or CO
2
, which are typically obtained by recirculating the fuel cell exhaust, and introduced directly to the SOFC anode. Commonly used Ni-based anodes provide the catalyst for the endothermic reforming reactions,
CH
4
+H
2
O=3H
2
+CO&Dgr;H°
298
=206 kJ/molCH
4
  (1)
CH
4
+CO
2
=2H
2
+2CO&Dgr;H°
298
=247 kJ/molCH
4
  (2)
However, maintaining appropriate gas composition and temperature gradients across a large area SOFC stack is challenging. See, Janssen, G. J. M., DeJong, J. P., and Huijsmans, J. P. P. Internal reforming in state-of-the-art SOFCs. 2nd European Solid Oxide Fuel Cell Forum, 163-172, Ed. by Thorstense, B. (Oslo/Norway, 1996); and Hendriksen, P, V., Model study of internal steam reforming in SOFC stacks. Proc. 5th Int. Symp. on Solid Oxide Fuel Cells, 1319-1325, Ed. by U. Stimming, S. C. Singhal, H. Tagawa, and W. Lehnert (Electrochem, Soc., Pennington, 1997).
For instance, if the reforming reactions are slow, then insufficient H
2
is supplied to the SOFCs. On the other hand, fast reforming reactions cause cooling localized near the fuel inlet, leading to poor cell performance, and possible cell fracture. Thus, current SOFC stacks of the prior art do not take full advantage of internal reforming; rather, they employ a combination of ≈75% external and 25% internal reforming of hydrocarbon fuels. See, Ray, E. R. Westinghouse Tubular SOFC Technology, 1992 Fuel Cell Seminar, 415-418 (1992).
SOFCs can in principle operate by direct electrochemical oxidation of a hydrocarbon fuel. This approach would be desirable since it eliminates the problems with internal reforming mentioned above, and the theoretical maximum fuel efficiency is as good or better than that for reforming. However, prior art attempts with SOFCs operating at temperatures T
c
=900-1000° C. with methane fuel have been less than satisfactory: either power densities were very low or carbon deposition was observed. See, Putna, E. S., Stubenrauch, J., Vohs, J. M. and Gorte, R. J. Ceria-based anodes for the direct oxidation of methane in solid oxide fuel calls,
Langmuir
11, 4832-4837 (1995); and Aida, T., Abudala, A., Ihara, M., Komiyama, H. and Yamada, K. Direct oxidation of methane on anode of solid oxide fuel cell. Proc. 4th Int. Symp. on Solid Oxide Fuel Cells, 801-809, Ed. by Dokiya, M., Yamamoto, O., Tagawa, H. and Singhal, S. C, (Electrochem. Soc. Pennington, 1995).
Recently, SOFCs have been developed to produce high power densities with hydrogen at reduced temperatures, T
c
=600-800° C. See, Huebner, W., Anderson, H. U., Reed, D. M., Sehlin, S. R. and Deng, X. Microstructure property relationships of NiZrO
2
anodes. Proc. 4th Int. Symp. on Solid Oxide Fuel Cells, 696-705, Ed. by Dokiya, M., Yamamoto, O., Tagawa, H. and Singhal, S. C. (Electrochem. Soc. Pennington, 1995); daSouza, S., Visco, S J. and DeJonghe, L. C. Thin-film solid oxide fuel cell with high performance at low-temperature.
Solid State Ionics
98, 57-61 (1997); Fung, K-Z., Chen, J., Tanner, C. and Virkar, A. V. Low temperature solid oxide fuel cells with dip-coated YSZ electrolytes. Proc. 4th Int. Symp. on Solid Oxide Fuel Cells, 1018-1027, Ed. by Dokiya, M., Yamamoto, O., Tagawa, H. and Singhal, S. C. (Electrochem. Soc. Pennington, 1995); Minh, N. Q. Development of thin-film solid oxide fuel cells for power generation applications. Proc. 4th Int. Symp. on Solid Oxide Fuel Cells, 138-145, Ed. by Dokiya, M., Yamamoto, O., Tagawa, H. and Singhal, S. C. (Electrochem. Soc. Pennington, 1995); Godickemeier, M., Sasaki, K. and Gauckler, L. J. Current-voltage characteristics of fuel cells with ceria-based electrolytes. Proc. 4th Int. Symp. on Solid Oxide Fuel Cells, 1072-1081, Ed. by Dokiya, M., Yamamoto, O., Tagawa, H. and Singhal, S. C. (Electrochem. Soc. Pennington, 1995); Tsai, T. and Barnett, S. A. Increased solid-oxide fuel cell power density using interfacial ceria layers.
Solid State Ionics
98, 191-196 (1997); and Tsai, T., Perry, E. and Barnett, S. Low-temperature solid-oxide fuel cells utilizing thin bilayer electrolytes.
J. Electrochem. Soc
., 144, L130-L132 (1997). However, such systems have not been considered or used for direct-hydrocarbon operation, because carbon deposition reaction rates decrease with decreasing temperature. In fact, there are no known reports SOFC operation on hydrocarbons at T
c
<800° C.
OBJECTS OF THE INVENTION
There are a considerable number of problems and the deficiencies associated with the use of hydrocarbons with solid oxide fuel cells. There is a demonstrated need for the use of such fuels in an efficient, economical fashion so as to improve the viability of the related technology.
Accordingly, it is an object of the present invention to provide various solid oxide fuel cells and/or components which can be used with hydrocarbon fuels thereby overcoming various deficiencies and shortcomings of the prior art, including those outlined above. It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all instances, to every aspect of the present invention. As such, the following objects can be used in the alternative with respect to any one aspect of the present invention.
It can be an object of the present invention to increase the rate of hydrocarbon oxidation so as to increase and/or otherwise provide useful power densities. Such densities can be increased and/or provided utilizing various catalytic metals in the fabrication of fuel cell anodes, such anodes as can be used in conjunction with a ceria material.
It can be an object of the present invention to utilize solid oxide fuel cells and/or components thereof for low temperature direct hydrocarbon oxidation.
It can also be an object of the present invention to provide various anodes and related cellular components having small particle size obtainable by sputter deposition processes and/or related fabrication techniques.
It can also be an object of the present invention to provi

Affiliated with

Also associated with

Rating

Direct hydrocarbon fuel cells does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Direct hydrocarbon fuel cells, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Direct hydrocarbon fuel cells will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2482610