CO Gas Sensors

Carbon monoxide is one of the most common and dangerous pollutants present in the environment dne to emissions from automated vehicles, aircraft, natural gas 

FIGURE 1.14 COj sensitivity as a function of CO2 concentration for LajOj-doped Sn02 sensor. (Reprinted from Sens. Actuators B, 62, Kim D. H., Yoon J. Y., Park H. C., and Kim K. H., CO2 sensing characteristics of Sn02 thick film by coating lanthanum oxide, 61-66, 2000, with permission from Elsevier.) 

The basic mechanism of the semicondncting metal oxide CO sensors relies on the condnctivity changes experienced by the n-type semiconducting metal oxide material when snrface chemisorbed oxygen reacts with reducing gases such as carbon monoxide (CO) or methane (CH4) at elevated temperatures. The overall reactions 

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Du, N., et al., Homogeneous coating ofAu andSn02 nanocrystals on carbon nanotubes via layer-by-layer assembly a new ternary hybrid for a room-temperature CO gas sensor. Chemical Communications, 2008(46) p. 6182-6184. 

V. Demarne and A. Grisel. An integrated low-power thin-film CO gas sensor on silicon . Sensors and Actuators 13 (1988), 301-313. 

As CO is highly toxic, and causes respiratory problems, its elimination is quite important Industrially, CO elimination is required for C02 laser application, and the production of pure hydrogen for fuel cells. Catalysis testing of the reaction has been performed, independently, with an IR gas-sensor by Hoffmann et al. and with a combustible CO gas sensor by Yamada et al. [25, 26]. In both groups, C02 produced by CO oxidation was quantified by an IR gas-sensor. 

Dilute CO elimination from air has been rapidly evaluated using CO gas sensors [25, 26]. The oxidation of 1 vol% CO in air was carried out under atmospheric pressure from 30 to 150 °C with a ramp rate of 2°C min-1. The CO concentration of an effluent from the reactor was continuously determined by the CO gas sensor. Fig. 8.1 shows the output signal and CO conversion determined by the CO gas sensor, and the CO conversion determined by FID-GC, for CO oxidation over Rh/Ti02. This indicates that the CO concentration decreases with increasing temperature, i.e., the CO conversion rate increases at higher temperature. The closed circles in Fig. 8.1 indicate the CO conversion determined by gas chromatography. The conversion curve calculated from the output signals of the CO gas sensor is... 

Fig. 8.2 Output signal changes of five parallel CO sensors with increasing catalytic reaction temperature. The catalysts whose effluents were analyzed by CO gas sensors were Rh/Sn02, Rh/W03, Rh/Si02, Rh/Ti02, Rh/Ce02 (reproduced by permission of Elsevier from [19]).

Fig. 8.5 Time courses of output signals of semiconductor-type oxygenate sensors, potentiometric CO sensor and ND-IR C02 sensors. The delay of CO gas sensor was due to the resistance of active carbon filter which removes oxygenate compounds (reproduced by permission of Elsevier from [19]).

Describe the construction of a tin oxide-based CO gas-sensor paying particular attention to essential design features. 

Monitoring pollutants in a variety of composition ranges in motor vehicle and chemical process exhaust gases is a major area of research in pollution abatement technology. Low-temperature CO oxidation catalysts are needed for zero emission vehicles, CO gas sensors, selective oxidation of CO in H2 rich streams in fuel cell applications,1,2 and in closed-cycle C02 lasers used for remote sensing in space applications.3"5 Effective oxidation of CO during... 

PEVD was developed initially in the course of fabricating type III potentiometric sensors for gaseous oxide (CO, SO, and NO ) detection. Three kinds of PEVD products (NaNOj, Na2C03, and Na SO ) were deposited as the auxiliary phases at the working electrode of NO, CO, and SO sensors, respectively. Because of the underlying similarities, all discussion here will focus on CO gas sensors. Cases of depositing NaNOj and Na SO auxiliary phases for type III NO and SO potentiometric sensors, respectively, can be treated analogously. 

Fig. 10 PEVD process design for applying an auxiliary phase (NagCOg) at the working electrode of a type III potentiometric CO gas sensor.

Fukui K and Nishida S. CO gas sensor based on Au-La203 added Sn02 ceramics with siliceous zeolite coat. Sens Actuators B 1997 45(2) 101-106. 

Ikeda, S., Kondo, T. Kato, S., Ito, K., Nomura, K. and Fujita, Y. (1995) Carbon dioxide sensor using solid electrolytes with zirconium phosphate framework (2). Properties of the CO, gas sensor using Mgi.i5Zr4P5 7810.30,4 as electrolyte. Solid-State Ionics, 79, 354—7. 

Ferrocene can be used to detect carbon monoxide (CO) by coordination, which increases the electron acceptability by the formation of a stable Fe-CO bond. Kim et al.222 have synthesized and investigated a ferrocenyl-based dendrimer as a CO gas sensor. The metalloden-drimer sensor showed a linear increase by 10 times up to 40% volume concentration, above which it was saturated. The transient responses exhibited a delay time of 50 seconds, a rising time of 150 seconds, and a falling time of 420 seconds, which were fair for a gas sensor when the diffusion time of gas into the chamber and the continued reaction with the remaining gas in the chamber after the introduction of the gas has been terminated are considered. 

Nafion membranes have been used in gas sensors, e.g. (i) to determine CO gas (CO gas sensor) by setting the working electrode and counter electrode on a glass substrate and by covering the electrodes with a Nafion recast membrane because Nafion polymer is relatively permeable to 02, CO and C02 (working electrode ... 

CO gas sensors have a myriad of applications, not only for home safety, but also in measuring atmospheric concentrations, in the exhaust of cars, and for process monitoring in industrial plants. 

Bhoga SS, Singh K (1999) A new Na glass-dispersed Na CO composite for a solid state electrochemical CO gas sensor. J Solid State Electrochem 3 258-263... 

Singh K, Ambekar P, Bhoga SS (2002) Eerroelectric dispersed composite solid electrolyte for CO gas sensor. In Chowdari BVR, Prabaharan SRS, Yahaya M, Talib lA (eds) SoUd state ionics trends in the new millennium. World Scientific Publishing, Singapore, pp 469-476... 

Ozaki et al. (2000) found that long term stability of SnO -based gas sensors can be achieved by sulfuric acid treatments as well. Sulfuric acid treatment of the sensor element was carried out in two ways in one a sulfuric acid solution is used instead of water and is added to the mixture of SnO and alumina powders used for preparing a paste, and in the other the obtained sensor element is dipped into a sulfuric acid solution for 2 s, dried for 3 min, and heated at 600 °C for 5 min. While a notable improvement in the stability and reliability of the SnO -based CO gas sensor has been achieved, and this is of practical importance, the mechanism of the sulfuric acid treatment is unknown at present. Ozaki et al. (2000) supposed that, due to formation of the sulfate species at the surface of the SnO, the formation of the surface hydroxyl groups is being blocked or reduced. The concentration change of surface hydroxyl groups is one of the main reasons of the long-term drift of the resistance of the SnOj-based gas sensors (Korotcenkov and Cho 2011 Ihokura and Watson 1994). 

OzaM Y, Suzuki S, Morimitsu M, Matsunaga M (2000) Enhanced long-term stability of SnO -based CO gas sensors modified by sulfuric acid treatment. Sens Actuators B Chem 62 220-225 Panchapakesan B, DeVoe DL, Widmaier MR, Cavicchi R, Steve SS (2001) Nanoparticle engineering and control of tin oxide microstructures for chemical microsensor applications. Nanotechnology 12 336-349 Papadopoulos CA, Vlachos DS, Avaritsiotis JN (1997) Effect of surface catalysts on the long-term performance of reactively sputtered tin and indium oxide gas sensors. Sens Actuators B Chem 42 95-101 Park CO, Akbar SA (2003) Ceramics for chemical sensing. J Mater Sci 38 4611-4637... 

Yuasa M, Masaki T, Kida T, Shimanoe K, Yamazoe N (2009) Nano-sized PdO loaded SnO nanoparticles by reverse micelle method for highly sensitive CO gas sensor. Sens Actuators B 136 99-104 Zhang J, Colbow K (1997) Surface silver clusters as oxidation catalysts on semiconductor gas sensors. Sens Actuators B 40 47-52... 

Very interesting results were reported by Rocchia et al. (2003). Experiments carried out by the authors of this chapter showed that, with a surface modification by 3-amino-1-propanol, one can fabricate PSi-based conductometric devices that are sensitive to CO. Unfortunately, the chemical nature of the surface species both before and after the binding of CO is not clear at this time. In addition, the detection limit given in this work is still far from market requirements, but the reversibility and low cost of this system represents a starting point for future development of PSi-based CO gas sensors. 

Marnellos G, Stoukides M (1998) Ammonia synthesis at atmospheric pressure. Science 282 98-100 Marques FMB, Wirtz GP (1991) Electrical properties of ceria-doped yttria. J Am Ceram Soc 74 598-605 Marques FMB, Kharton W, Naumovich EN, Shaula AL, Kovalevsky AV, Yaremchenko AA (2006) Oxygen ion conductors for fuel cells and membranes selected developments. Sohd State Ionics 177 1697-1703 Marsal A, Comet A, Morante JR (2003a) Study of the CO and humidity interference in La doped tin oxide CO gas sensor. Sens Actuators B 94 324-329... 

Marsal A, Dezanneau G, Cornet A, Morante JR (2003b) Study of the CO and humidity interference in La doped tin oxide CO gas sensor. Sens Actuators B 95 266-270... 

Table 6.4 Materials used in solid-state electrochemical CO gas sensors...

Kim D-H, Yoon J-Y, Park H-C, Kim K-H (2001) Fabrication and characteristics of CO -gas sensor using Li CO -LijPO -AljOj electrolyte and LiMn O reference electrode. Sens Actuators B 76 594-599 Kleperis J, Bayars G, Vaivars G, Kranevskis A, Lusis A (1992) Solid electrolytes in sensor technology. Sov Electrochem 28 1181-1186... 

Lee C, Akbar SA, Park CO (2001) Potentiometric type CO gas sensor with lithium phosphorous oxynitride electrolyte. Sens Actuators B 80 234-242... 

Nitta M, Haradome M (1979) Thick-film CO gas sensors. IEEE Trans El Dev ED-26(3) 247-249 Patil A (2011) ZnO thick films gas sensor electrical, structural and gas sensing characteristics with different dopants. Lambert Academic, Saarbriicken... 

Schweizer-Berberich M, Strathmann S, Gopel W, Sharma R, Peyie-Lavigne A (2000) Filters for tin dioxide CO gas sensors to pass the UL2034 standard. Sens Actuators B 66 34-36 Shen CY, Huang CP, Huang WT (2004) Gas-detecting properties of surface acoustic wave ammonia sensors. Sens Actuators B 101 1—7... 

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