- 2014-12-01 (x)
- Hospitals, Chronic Disease -- statistics & numerical data -- Ohio -- Cleveland (x)
- Litt, Morton H. (x)
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Show moreField of the invention: The invention relates to a method for casting a solid polymer electrolyte useful in fuel cells operated at elevated temperatures. More specifically, the invention is related to the use of a method of casting polymer electrolyte membranes intended for use in fuel cells operating on liquid fuels, the casting method involving casting the polymer electrolyte membrane directly from an acid solution. The membranes cast by this method demonstrate unexpectedly improved conductivity. Background of the invention: In the past decade considerable effort has gone into the development and characterization of perfluorosulfonic acid polymer electrolytes such as Nafion. These efforts have shown that polymer electrolyte membranes (PEM) offer a number of advantages over conventional electrolytes when used in electrochemical devices such as fuel cells and water electrolyzers. U.S. Pat. No. 5,525,436, entitled "Proton Conducting Polymers", the disclosure of which is incorporated herein by reference, discloses the use of polymer electrolyte membranes, for example polybenzimidazole (PBI) doped with phosphoric acid, which are capable of conducting protons at temperatures of up to at least 200.degree. C. These membranes, therefor, avoid prior art problems related to dehydration of the membrane. Further, disadvantages due to poisoning of the electrode catalysts and fuel crossover are overcome by the novel polymer electrolyte membranes disclosed in the patent. The preparation of the membranes of the patent involves first casting the membrane film from an appropriate solution, such as dimethyl acetamide (DMAc), and then doping the film with the desired acid constituent. Conductivity in the range of from 0.01 to 0.04 S/cm for temperatures from 130.degree. C.-190.degree. C. and water vapor partial pressures up to 1 atmosphere were recorded for H.sub.3 PO.sub.4 doped PBI films. It has now been discovered that the conductivity of polymer electrolyte membranes of the type discussed above may be significantly and unexpectedly enhanced by preparation of the membrane from a solution of the doped polymer in an acid. For example, a PBI film doped with H.sub.3 PO.sub.4 and prepared from trifluoroacetic acid (TFA) solution exhibits conductivity measured at 0.04-0.08 S/cm, as compared to the lower conductivity measured for PBI membranes cast from DMAc and subsequently doped. It has further been discovered that the economics of membrane production can be reduced by casting the PBI membranes directly from a casting solution containing H.sub.3 PO.sub.4 and including trifluoroacetic acid (TFA) as a solvent.It is, therefore, an object of the subject invention to provide a method for casting a solid polymer electrolyte membrane which does not suffer from known problems associated with catalyst stability and activity, and which demonstrates enhanced conductivity.
http://www.google.com/patents?vid=USPAT6099988
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Show moreField of the invention: The invention relates to a method for casting a solid polymer electrolyte useful in fuel cells operated at elevated temperatures. More specifically, the invention is related to the use of a method of casting polymer electrolyte membranes intended for use in fuel cells operating on liquid fuels, the casting method involving casting the polymer electrolyte membrane directly from an acid solution. The membranes cast by this method demonstrate unexpectedly improved conductivity. Background of the invention: In the past decade considerable effort has gone into the development and characterization of perfluorosulfonic acid polymer electrolytes such as Nafion. These efforts have shown that polymer electrolyte membranes (PEM) offer a number of advantages over conventional electrolytes when used in electrochemical devices such as fuel cells and water electrolyzers. U.S. Pat. No. 5,525,436, entitled "Proton Conducting Polymers", the disclosure of which is incorporated herein by reference, discloses the use of polymer electrolyte membranes, for example polybenzimidazole (PBI) doped with phosphoric acid, which are capable of conducting protons at temperatures of up to at least 200.degree. C. These membranes, therefor, avoid prior art problems related to dehydration of the membrane. Further, disadvantages due to poisoning of the electrode catalysts and fuel crossover are overcome by the novel polymer electrolyte membranes disclosed in the patent. The preparation of the membranes of the patent involves first casting the membrane film from an appropriate solution, such as dimethyl acetamide (DMAc), and then doping the film with the desired acid constituent. Conductivity in the range of from 0.01 to 0.04 S/cm for temperatures from 130.degree. C.-190.degree. C. and water vapor partial pressures up to 1 atmosphere were recorded for H.sub.3 PO.sub.4 doped PBI films. It has now been discovered that the conductivity of polymer electrolyte membranes of the type discussed above may be significantly and unexpectedly enhanced by preparation of the membrane from a solution of the doped polymer in an acid. For example, a PBI film doped with H.sub.3 PO.sub.4 and prepared from trifluoroacetic acid (TFA) solution exhibits conductivity measured at 0.04-0.08 S/cm, as compared to the lower conductivity measured for PBI membranes cast from DMAc and subsequently doped. It has further been discovered that the economics of membrane production can be reduced by casting the PBI membranes directly from a casting solution containing H.sub.3 PO.sub.4 and including trifluoroacetic acid (TFA) as a solvent. It is, therefore, an object of the subject invention to provide a method for casting a solid polymer electrolyte membrane which does not suffer from known problems associated with catalyst stability and activity, and which demonstrates enhanced conductivity.
http://www.google.com/patents?vid=USPAT5716727
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Show moreField of the invention: The invention-relates to a solid polymer electrolyte useful in fuel cells operated at elevated temperatures. More specifically, the invention is related to the use of a polymer electrolyte membrane capable of conducting protons at temperatures up to at least 200.degree. C. in fuel cells operating on liquid fuels. Background of the invention: In the past decade considerable effort has gone into the development and characterization of perfluorosulfonic acid polymer electrolytes such as Nafion. These efforts have shown that polymer electrolyte membranes (PEM) offer a number of advantages over conventional electrolytes when used in electrochemical devices such as fuel cells and water electrolyzers. Unfortunately, these electrolytes must remain hydrated to retain ionic conductivity, which limits their maximum operating temperature to 100.degree. C. at atmospheric pressure. This disadvantage of known PEM materials, therefore, is highlighted in those systems in which a polymer electrolyte with high conductivity at temperatures in excess of 100.degree. C. would be useful. One such application is the H.sub.2 /O.sub.2 fuel cell that utilizes reformed hydrogen from organic fuels (methane, methanol, etc.) which will have a certain amount of CO that poisons the electrode catalysts. Another such application is the direct methanol fuel cell. Present direct methanol-air fuel cell configurations are severely limited by the lack of sufficiently active catalysts for the methanol anode, and to a lesser extent, the oxygen cathode. This is a direct result of catalyst poisoning caused by carbon monoxide produced by the fuel at operating temperatures of about 100.degree. C. or lower. Another disadvantage of known PEM methanol-air fuel cells is seen in poor performance of the fuel cells due to the high rate of methanol cross-over from the anode to the cathode through the membrane, which results in a loss of efficiency via chemical reaction of the fuel with oxygen and consequent depolarization of the cathode. The use of solid polymer electrolytes offers new opportunities to overcome these catalyst stability and activity problems, provided the polymers selected are stable and retain reasonable ionic conductivity at temperatures approaching 200.degree. C., avoiding anode/cathode poisoning effects. Further, such polymers should have other desirable properties, such as low methanol permeability to reduce the efficiency losses resulting from crossover. It has now been discovered that films comprising polymers containing basic groups that can form complexes with stable acids or polymers containing acidic groups provide a viable alternative to known PEM's and other conventional electrolytes. Polybenzimidazole (PBI) which has been doped with a strong acid, such as phosphoric acid or sulfuric acid, is an example of a suitable polymer.
http://www.google.com/patents?vid=USPAT5525436
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Show moreField of the invention: The invention relates to a method for casting a solid polymer electrolyte useful in fuel cells operated at elevated temperatures. More specifically, the invention is related to the use of a method of casting polymer electrolyte membranes intended for use in fuel cells operating on liquid fuels, the casting method involving casting the polymer electrolyte membrane directly from an acid solution. The membranes cast by this method demonstrate unexpectedly improved conductivity. Background of the invention: In the past decade considerable effort has gone into the development and characterization of perfluorosulfonic acid polymer electrolytes such as Nafion. These efforts have shown that polymer electrolyte membranes (PEM) offer a number of advantages over conventional electrolytes when used in electrochemical devices such as fuel cells and water electrolyzers. U.S. Ser. No. 08/332,869, entitled "Proton Conducting Polymers", the disclosure of which is incorporated herein by reference, discloses the use of polymer electrolyte membranes, for example polybenzimidazole (PBI) doped with phosphoric acid, which are capable of conducting protons at temperatures of up to at least 200.degree. C. These membranes, therefore, avoid prior art problems related to dehydration of the membrane. Further, disadvantages due to poisoning of the electrode catalysts and fuel crossover are overcome by the novel polymer electrolyte membranes disclosed in the patent. The preparation of the membranes of the patent involves first casting the membrane film from an appropriate solution, such as dimethyl acetamide (DMAc), and then doping the film with the desired acid constituent. Conductivity in the range of from 0.01 to 0.04 S/cm for temperatures from 130.degree. C.-190.degree. C. and water vapor partial pressures up to 1 atmosphere were recorded for H.sub.3 PO.sub.4 doped PBI films. It has now been discovered that the conductivity of polymer electrolyte membranes of the type discussed above may be significantly and unexpectedly enhanced by preparation of the membrane from a solution of the doped polymer in an acid. For example, a PBI film doped with H.sub.3 PO.sub.4 and prepared from trifluoroacetic acid (TFA) solution exhibits conductivity measured at 0.04-0.08 S/cm, as compared to the lower conductivity measured for PBI membranes cast from DMAc and subsequently doped. It has further been discovered that the economics of membrane production can be reduced by casting the PBI membranes directly from a casting solution containing H.sub.3 PO.sub.4 and including trifluoroacetic acid (TFA) as a solvent.It is, therefore, an object of the subject invention to provide a method for casting a solid polymer electrolyte membrane which does not suffer from known problems associated with catalyst stability and activity, and which demonstrates enhanced conductivity.
http://www.google.com/patents?vid=USPAT6025085
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Show moreBackground of invention: The invention described herein was made in the performance of work under NASA Grant Number NAG3-446 and in subject with the provisions of 35 U.S.C. 202. The present application relates to new silicon based preceramic polymers useful in the production of silicon carbide reinforcement fibers, and to the novel synthesis procedures by which such polymers may be produced. It is well known that silicon carbide can provide highly desirable and unique properties due to its chemical inertness, high temperature stability, semi-conductor properties, and especially its extreme hardness. Fibers of silicon carbide can be used in a wide variety of applications, particularly as reinforcements for composites. The problems encountered in prior attempts to utilize silicon carbide reinforcements in most applications were due to the great difficulty experienced in attempting to form the silicon carbide reinforcement material into the desired configuration. One suggested means of overcoming these problems was to employ silicon based preceramic polymers, such as polycarbosilanes. These polycarbosilanes are prepared by a controlled pyrolysis of polydimethylsilanes, which in turn are typically prepared from dimethyldichlorosilane and Na metal as shown below. ##STR2## wherein R is hydrogen or methylFrom the hexane soluble non-volatile polymer fraction, fibers could be melt spun, which could be subsequently cross-linked by surface oxidation in air, and then pyrolized at high temperature in an inert atmosphere, to ultimately yield silicon carbide fibers. Such procedures are, for example, suggested by Yajima et al., synthesis of continuous silicon carbide fibers with high tensile strength and high Young's modulus, Journal of Materials Science, 13, 1978 (2569-2575), who postulated a structure as follows: ##STR3## The structure has many cyclized units in it and it is well known that poly(dimethylsilanes) tend to cyclize and volatilize when heated. It was subsequently suggested that volitilization could be prevented by replacing some of the methyl groups by phenyl groups; however the yield of silicon carbide in fact dropped, since the ultimate percent of volatilization increased. These procedures also tended to result in the formation of significant yields of graphite. In general, the methods heretofore employed produced a rather low "char yield", that is to say a rather low ultimate yield of silicon carbide as a function of the preceramic polymer (after it had been formed into the desired shape, but prior to the oxidative cross linking and/or high temperature pyrolization steps.) It will of course be obvious that such weight losses are highly undesirable, not only from the economic point of view but also from the point of view of the resultant inherent problems of shrinkage, displacement and the like.
http://www.google.com/patents?vid=USPAT4777234
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