- 2014-12-01 (x)
- 1924-10-20 (x)
- Savinell, Robert F. (x)
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Show moreBackground of the invention: The present invention relates to the gaseous detection arts. It finds particular application in conjunction with metal oxide sensors for detection of carbon monoxide, and will be described with particular reference thereto. The invention is also applicable to the detection of other gaseous reducing chemicals, such as hydrogen, hydrogen sulfide, hydrocarbons, and organic vapors, including toluene. The quality of indoor air affects the health and well-being of building occupants. Concerns over the control and improvement of indoor air quality have lead to the development of a number of gaseous sensors capable of detecting toxic and pollutant gases, such as carbon monoxide, carbon dioxide, hydrogen sulfide, chlorine, nitrogen oxides, ammonia, and sulfur dioxide, as well as combustible gases, such as hydrogen, methane, and other flammable organic vapors. Metal oxide-based sensors using oxides of zinc, tin, titanium, and other semiconductive oxides have been evaluated for their abilities to detect specific gases. Tin oxide-based sensors have shown particular promise as they exhibit a high sensitivity to certain gases at relatively low operating temperatures. Such sensors detect gases by exhibiting a measurable change in the resistance of the bulk oxide when a gas or chemical vapor is adsorbed onto the surface of the oxide. The sensitivity of a sensor is influenced by the microstructure of the sensing surface. Surface area to volume ratio, grain size, and pore size of the metal oxide particles which comprise the surface are understood to affect the performance of the sensor. Thin film sensors are desirable because of their relatively small size and low power consumption. Such sensors may be prepared in a number of ways, including sputtering, physical vapor deposition, and chemical vapor deposition. Sputtering and physical vapor deposition techniques produce relatively thin films, of the order of a few hundred nanometers or less. Although such films exhibit good sensitivity to gases to be detected, they often have poor stability due to their low mechanical strength. Sensors produced by chemical vapor deposition tend to suffer from poor film uniformity as the film often shows an "island" texture. Recently, sol-gel technology has been developed for the preparation of tin oxide powders. Two sol-gel synthesis routes are known. One route involves hydrolysis of tin alkoxide to the oxide and is discussed by Wilson, et al. ("Sol-Gel Materials for Gas Sensing Applications", Sensors and Actuators B., 18-19 pp. 506-510 (1994)) and Takahata ("Tin oxide Sensors, Development and Applications," in Chemical Sensor Technology, Vol 1, pp. 39-55 (Seiyama, Ed. 1988)). Another route employs hydrolysis of tin (IV) chloride, as disclosed by Vogel, et al.
http://www.google.com/patents?vid=USPAT6134946
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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 moreField of the invention: The present invention relates to a polymeric material particularly adapted for use as a polymer electrolyte membrane in a fuel cell. Specifically, the present invention relates to rigid rod copolyimide polymers containing sulfonic acid groups. More specifically, the present invention relates to a copolyimide containing sulfonic acid constituents, having a rigid rod, liquid crystalline structure, and which incorporates bulky, displacing or angled monomers along the polymer chain. Incorporation of bulky monomers in the polymer chain creates regions of access along the chain, thereby exposing sulfonic acid groups, also located along the chain, which in turn enhances conductivity properties of the polymer. Background of the invention: Solid, proton conducting polymer electrolyte membranes (PEMs) provide several key features in present technology fuel cells. These features include providing a conduction medium for protons, supporting and separating electrodes, and separating fuel from oxidizer. Consequently, polymer electrolyte membranes must exhibit ion exchange properties that allow sufficient conductivities to be achieved. In addition, such membranes must exhibit high chemical and mechanical resistance under extreme operating conditions which are typically encountered in many fuel cell applications. An example of a commercially available polymer electrolyte membrane is Nafion.RTM. and is available from DuPont. Nafion.RTM. is adequate for use in most current fuel cell applications, but exhibits several deficiencies. It has poor conductivity at low relative humidities and can not easily be used at temperatures above 80.degree. C. because it dries out. Furthermore, Nafion.RTM. exhibits high osmotic drag which contributes to difficulties in water management at high current densities. In addition, high methanol permeability in Nafion.RTM. contributes to detrimental fuel cross over, in which fuel passes across the anode, through the Nafion.RTM. membrane and to the cathode. Consequently, in instances of fuel cross over, methanol is oxidized at the cathode and fuel cell efficiency decreases. It would be beneficial to identify polymeric materials suitable for use as polymer electrolyte membranes in a fuel cell that exhibit improved properties over currently available materials. Specifically, it would be desirable to provide a polymeric material that exhibits increased conductivity, improved thermal stability, reduced methanol permeability and improved mechanical properties over presently available polymer electrolyte membranes such as Nafion.RTM.. Summary of the invention: The present invention achieves all of the foregoing objectives and provides, in a first aspect, a rigid rod ion conducting copolymer comprising three types of monomers. The first monomer is a generally non-polar monomer that is capable of binding a diamine. The second monomer is a diamine monomer having sulfonic acid groups.
http://www.google.com/patents?vid=USPAT6586561
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