Methane sensor electrodes

Acetylcholineesterase and choline oxidase Enzyme immobilized over tetra-thiafulvalene tetracyanoquinodi-methane crystals packed into a cavity at the tip of a carbon-fiber electrode. The immobilization matrix consisted of dialdehyde starch/glutaraldehyde, and the sensor was covered with an outer Nafion membrane. The ampero-metric performance of the sensor was studied with the use of FIA system. An applied potential of +100 mV versus SCE (Pt-wire auxiliary electrode) and a carrier flow rate of 1 mL/min. The Ch and ACh biosensors exhibited linear response upto 100 pM and 50 pM, respectively. Response times were 8.2 s. [97]... 

In principle, this sensor is also applicable to CO measurement in the gas phase for it was possible to keep the enzyme stable in a wet medium behind the gas-permeable membrane. In comparison with other biocat-alytic gas-sensing devices, e.g. those for methane (Karube et al., 1982a) or NH3 and NO2 (Hikuma et al., 1980b) the sensor was more compact and its response was substantially faster. This enzyme electrode therefore represents a promising approach to novel gas sensors. 

Nitrogen dioxide can also be selectively detected by an electrode with a chalcogenide (Se6oOe28Sbi2) membrane, without interference from nitric oxide, sulfur dioxide, carbon monoxide, methane, and other gases. Another solid-state sensor for NO2 employs an alkaline nitrate electrolyte at a temperature of 800°C. 

Tin dioxide, an n-type semiconductor with a wide bandgap (3.6 eV at 300 K), has been widely studied as a sensor, a (photo)electrode material and in oxidation reactions for depollution. The performance of tin(iv) oxide is closely linked to structural features, such as nanosized crystallites, surface-to-volume ratio and surface electronic properties. The incentive for carbon-dioxide transformation into value-added products led to examination of the electroreduction of carbon dioxide at different cathodes. It has been recognised that the faradic yield and selectivity to carbon monoxide, methane, methanol, and formic acid rely upon the nature of the cathode and pH. ° Tin(iv) oxide, as cathode, was found to be selective in formate formation at pH = 10.2 with a faradic yield of 67%, whereas copper is selective for methane and ethene, and gold and silver for carbon monoxide. Nano-tin(iv) oxide has been shown to be active and selective in the carboigrlation of methanol to dimethyl carbonate at 150 °C and 20 MPa pressure. The catalyst was recyclable and its activity and selectivity compare with that of soluble organotins (see Section 21.5). 

Amperometric and conductimetric gas sensors have been devised for the detection of oxygen, hydrogen, ammonia, sulfur dioxide and methane. Enzyme-based biosensors such as cholesterol or glucose electrodes for blood analysis depend on the oxidation of cholesterol or glucose oxidase, respectively, to produce hydrogen peroxide that is detected amjjerometricaUy (Fig. 3). 

Although IL electrolytes provide partial selectivity, the primary selectivity of an IL-electrochemical sensor comes from the redox properties of the analyte observed using amperometric methods, wherein the electrical current generated by reaction of an analyte at an electrode at a fixed or variable potential is measured [22]. We have shown redox chemistry that occurs only in ILs and can be exploited to enhance sensor performance [202], As shown in Fig. 2.16, we discovered that at platinum electrode in [NTf2]-based ionic liquids (ILs), facile methane electro-oxidation is observed suggesting a unique catalytic Pt-INTfj] interface for electron-transfer reaction of methane at room temperature. Little methane electro-oxidation signals are observed in ILs with other anions. In this experiment, an oxygen reduction process... 

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