Electrode carbon monoxide sensors

Carbon monoxide sensor. Carbon monoxide is a toxic air pollutant originating from incomplete combustion of fuels in burners or engines. Despite a strong demand for a very reliable carbon monoxide sensor, the only available sensor was based on an electrochemical type until recently. In this type sensor, selectivity and sensitivity for CO can often be enhanced by selecting elecrode materials and electrode potential appropriately, but several disadvantages are encountered, such as, short life, difficult maintenance and a rather expensive price. 

Chemical sensors (i) Gases (e.g. blood oxygen electrode, carbon monoxide detector) (ii) pH and ions (e.g. pH meter, potassium-selective elecbode) and (iii) optical oximetry (e.g. pulse oximeby for non-invasive monitoring of blood oxygenation). 

It is also essential to know the cross-sensitivity of the zirconia single-crystal sensors to other gases. Sensors with porous Pt electrodes are known to be sensitive to gases such as CO at low temperatures [41], and in fact, this cross-sensitivity has been proposed as a principle for carbon monoxide sensors at low temperatures by some researchers [42, 43]. This effect is attributed to the ability of CO to compete successfully with oxygen for adsorption sites on Pt at temperatures from 500°C to 650°C. It was observed that the zirconia single-crystal sensor with thin-film Pt-Zr02-Y2O3 electrodes is less sensitive to CO than similar polycrystalhne sensors with porous Pt electrodes, but small em/errors still occur at 300-360°C. 

Albery et al. (1987a) developed a carbon monoxide sensor based on the sequence of cytochrome oxidase and cytochrome c coupled to a modified gold electrode. The inhibition by CO was detected via the decrease of the oxygen reduction rate. The sensor is also applicable to the quantitation of other inhibitors of the respiratory chain. 

Low temperature carbon monoxide sensors based on the reversible carbon monoxide adsorptive poisoning of precious metal electrodes are also being developed by Los Alamos National Laboratory. The addition of metals such as ruthenium to the platinum electrode material greatly improves the hydrogen oxidation kinetics in the presence of CO. An amperometric sensor that senses the CO inhibition of the hydrogen oxidation can be fabricated from a platinum electrode, a proton conductor and a platinum ruthenium alloy electrode. While the... 

Thermal evaporation of PANI has been also developed to fabricate PANI thin film by vacuum deposition of PANI powder on the reference electrode [310]. The chemically synthesized PANI powder was formed in pellet type and the pelletized PANI was evaporated on glass substrates at a pressure of 10 mm Hg to form PANI thin film. The pre-cleaned glass substrate was covered uniformly with PANI thin film and this thin film was utihzed as a carbon monoxide sensor. Thus, thermal evaporation method could be used for thin film formation of conducting polymer nanomaterials [311-313]. 

Santhosh P, Manesh KM, Gopalan A, Lee K-P (2007) Novel amperometric carbon monoxide sensor based on multi-wedl carbon nanotubes grafted with polydiphenylamine-fabrication and performance. Sens Actuators B 125 92-99 Shai K, Wagner J (1982) Enhanced ionic conduction in dispersed solid electrolyte systems (DSES) and/or multiphase systems Agl-Al Oj, Agl-SiO, Agl-Ely ash, and Agl-AgBr. J Sohd State Chem 42 107-119 Shimizu Y, Yamashita N (2000) Solid electrolyte CO sensor using NASICON and perovskite-type oxide electrode. Sens Actuators B 64 102-106... 

A quartz plate equipped with a gold electrode on each face can detect the adsorption of mercury vapor on the gold. A carbon monoxide sensor can therefore be constructed since this gas reacts with mercury oxide at 210 liberating mercury vapor [224] which is detectable with the piezoelectric sensor. Similarly, the deposition of copper complexes on a quartz crystal is used to detect organophosphates [225] such as diisopropylmethylphosphonate (DIMP), and modified cyclodextrins are us to detect benzene vapors [226]. The piezoelectnc sensor is also used in the liquid phase to monitor the viscosity of fluids and gelation, and deduce, for example, the concentration of fibrinogen [227]. 

The direct anodic oxidation of cytochrome c at a bipyridyl-modified electrode has already been incorporated in enzyme electrodes for lactate, carbon monoxide, and hydrogen peroxide. Here, cytochrome c is reduced by cytochrome b2, CO oxidoreductase, or horseradish peroxidase and anodically reoxidized. Cytochrome c has also been applied to couple mitochondria and chloroplasts to redox electrodes (Albery et al. 1987). Although no practically applicable sensor has been constructed as yet, this principle offers a new avenue to the determination of inhibitors of photosynthesis or respiration (Cardosi and Turner, 1987). 

Figure 20.9 AGS, principles of operation. Cells for hydrogen sulfide, for carbon monoxide and for oxygen. For hydrogen sulfide sensor, the reference electrode helps to extend the working range of the sensor and improves the linearity of response. The electrochemical reactions consume the species present in the cell. This can be the anode itself (cell for oxygen), the electrolyte or even a reagent which should be present (oxygen is necessary for the cell detecting carbon monoxide).

Figure 8.16. Electric response of the sensors with different kind of electrodes in the presence of synthetic air, of carbon monoxide (300ppm/air) and nitrogen dioxide (100 ppm/air) at 500°C...

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. 

Liquid Electrolyte Sensors The construction of amperometric cells with liquid electrolytes for gas analysis does not differ principally from those for measurements in liquids. Differences can be found in the utilized membranes, electrolytes and electrode materials. Gases as carbon monoxide or nitrogen oxide can be determined only with catalytically activated... 

Misra SCK, Mathur P, Srivastava BK (2(X)4) Vacuum-deposited nanocrystalline polyaniline thin film sensors for detection of carbon monoxide. Sens Actuators A 114 30-35 Mulchandani AK, Wang CL (1996) Bienzyme sensors based modified electrodes. Electroanalysis 8 414-419 Muller JBA, Smith CE, Newton MI, Percival CJ (2011) Evaluation of coated QCM for the detection of atmospheric ozone. Analyst 136 2963-22968... 

Carbon monoxide detectors are in widespread use in the workplace and home. Metal oxide (e.g. Sn02) semiconductor and electrochemical sensors are commonly used, (a) Explain how an Sn02 sensor for CO works, (b) An electrochemical sensor employs platinum electrodes with aqueous sulfuric acid as the electrolyte. CO is oxidized at the anode. Write half equations for the anode and cathode reactions. Outline how the cell works as a quantitative sensor for CO. 

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). 

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