Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1999-06-28
2001-06-19
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S315000, C429S316000, C429S317000, C528S171000, C528S172000, C528S173000, C528S183000, C528S337000
Reexamination Certificate
active
06248480
ABSTRACT:
FIELD OF THE INVENTION
The field of the invention is polymer electrolytes.
BACKGROUND OF THE INVENTION
Most electrolytic cells and fuel cells utilize at least one cathode and one anode in an electrochemical reaction. Typically, a separator keeps a cathode and anode physically separated, and an electrolyte enables electrochemical contact between the two electrodes. In some instances, the separator and the electrolyte are two distinct functional elements. For example, NaCl electrolysis typically employs an asbestos diaphragm or a mercury intermediate electrode as a separator, and a highly alkaline NaCl solution as the electrolyte. However, utilizing a separator and a liquid electrolyte often has many disadvantages. Configurations with an electrolyte and a separator frequently require considerable space. Moreover, liquid electrolytes are often highly corrosive and pose potential leakage problems of the cell with subsequent loss of the electrolyte. Another problem with a liquid electrolyte is that such electrolytes tend to become readily contaminated.
In a polymer electrolyte, the separator and the electrolyte are combined in a single physical component. Generally, a polymer electrolyte carries ion exchange groups, such as sulfonate or phosphonate groups, on a polymeric structure. Depending on the molecular design of the polymer electrolyte, a single ion or an ion pair can migrate through the polymer. The use of polymer electrolytes is advantageous, because electrolysis cells or fuel cells can be configured in various space saving ways. Furthermore, since the polymer electrolyte is not liquid, leakage problems with consequent loss of the electrolyte are typically not encountered.
Many polymer electrolytes, such as poly(ethylene oxide)- and poly(propylene oxide) based compounds, or polysulfone- and polyvinylidene compounds, are relatively inexpensive and can be utilized in various applications. However, some of these electrolytes have relatively low ion conductivity and chemical stability limiting their practicability. Other polymer electrolytes are stable only at relatively low temperatures.
Low temperature stability is especially undesirable, because many electrochemical reactions can be run more efficiently at higher temperatures. For example, the efficiency of water electrolysis benefits from an increase in temperature due to a decrease in the thermodynamic potential and a decrease in electrode polarization. Temperatures in the range of 150° C. to 250° C. are particularly desirable because such temperatures allow for an excellent carbon monoxide tolerance. Moreover, temperatures in the range of 150° C. to 250° C. would enable the direct oxidation of ethanol, other alcohols and hydrocarbons.
To circumvent at least some problems of the low temperature stability, perfluorinated hydrocarbon sulfonate ionomers, such as Nafion™ (a perfluorinated hydrocarbon with sulfonic acid groups), have been developed. However, despite their enhanced chemical and thermal stability many difficulties still persist. One problem is that perfluorinated hydrocarbon sulfonate ionomers are relatively expensive. Another problem is that such ionomers tend to decompose at temperatures of about 80° C. and above when they are used over a prolonged period of time.
In recent years, new high temperature polymer electrolytes with improved physicochemical properties have been synthesized. For example, U.S. Pat. No. 5,548,055 and U.S. Pat. No. 5,633,098, both to Narang et al., demonstrate polymer electrolytes based on polysiloxanes and poly (alkylene oxides) with improved plasticity. In another example, U.S. Pat. No. 5,312,895 and U.S. Pat. No. 5,312,876, both to Dang, rigid “rod-type” para-ordered high temperature polymer electrolytes with solubility in water or in aprotic solvents are shown. In a further example, in U.S. Pat. No. 5,741,408 to Helmer-Metzmann, the author shows that the stability of a high temperature polymer electrolyte can be improved by cross-linking polymer electrolyte strands. In a still further example, in U.S. Pat. No. 5,403,675 to Ogata and Rikugata, high temperature polymer electrolytes, such as sulfonated rigid-rod polyphenylenes, are presented that can even operate in the absence of liquid water.
Significant progress in high temperature polymer electrolytes has been achieved with respect to thermal stability and mechanical properties. However, high temperature polymer electrolytes still suffer from a serious disadvantage. Almost all, or all high temperature polymer electrolytes contain aromatic hydrogen atoms that are prone to oxidation, which eventually leads to a decrease in performance and a loss of chemical and structural stability. Therefore, there is still a need to provide improved methods and compositions for electrochemically stable high temperature polymer electrolytes.
SUMMARY OF THE INVENTION
In accordance with the present inventive subject matter, compositions and methods are provided in which an electrolyte has a backbone that includes a plurality of aromatic constituents coupled together by at least one atom having a &pgr;-cloud, and in which a halogen atom and an ion exchange group are covalently bound directly to the backbone.
In one aspect of a preferred class of embodiments, the haloaromatic polymer electrolytes are high temperature resistant haloaromatic polymer electrolytes. In a more preferred class, the high temperature resistant haloaromatic polymer electrolytes comprise perhalogenated polyphenylenes, perhalogenated phenylene ethers, perhalogenated polyamides, perhalogenated polyesters, perhalogenated aromatic polycarbonates, perhalogenated polysulfones, perhalogenated polyurethanes, perhalogenated polyureas, perhalogenated polyimides, perhalogenated polybenzazoles, perhalogenated polyquinoxalines, or perhalogenated polyquinolines. In an even more preferred class, the perhalogenated polymers are perfluorinated polymers.
In another aspect of preferred embodiments, the haloaromatic polymer electrolytes have acidic groups as ion exchange groups, and in a more preferred class, the acidic groups are sulfonic acid groups, or phosphoric acid groups.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention.
REFERENCES:
patent: 4797457 (1989-01-01), Guiver et al.
patent: 5312876 (1994-05-01), Dang et al.
patent: 5312895 (1994-05-01), Dang et al.
patent: 5378550 (1995-01-01), Doddapaneni et al.
patent: 5403675 (1995-04-01), Ogata et al.
patent: 5548055 (1996-08-01), Narang et al.
patent: 5558959 (1996-09-01), Venugopal et al.
patent: 5602185 (1997-02-01), Stone et al.
patent: 5633098 (1997-05-01), Narang et al.
patent: 5741408 (1998-04-01), Helmer-Metzmann et al.
patent: 5886130 (1999-03-01), Trimmer et al.
patent: 6087031 (2000-07-01), Iwasaki et al.
Narang Subhash
Ventura Susanna
Fish Robert D.
Fish & Associates, LLP
Kalafut Stephen
SRI - International
Thompson Sandra Pateat
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