Carbon-oxygen sensors

Okamoto A, Suzuki Y, Yoshitake M, Ogawa S, Nakano N (1997) Gold-carbon composite thin films for electrochemical gas sensor prepared by reactive plasma sputtering. Nucl Instrum Methods Phys Res B 121 179-183 Polsky R, Gill R, Kaganovsky L, WiUner I (2006) Nucleic acid-functionalized Pt nanoparticles catalytic labels for the amplified elecfrochemical defecfion of biomolecules. Anal Chem 78 2268-2271 Rabinovich L, Lev O (2001) Sol-gel derived composite ceramic carbon electrodes. Electroanalysis 13(4) 265-275 Rabinovich L, Gun J, Tsionsky M, Lev O (1997) Euel-ceU type ceramic-carbon oxygen sensors. J Sol-Gel Sci Technol 8 1077-1081... 

Rabinovich, L., J. Gun, M. Tsionsky, and O. Lev, 1997. Fuel-cell type ceramic-carbon oxygen sensors. J Sol-Gel Sci Technol 8 1077-81. 

The measurement of temperature is necessary for the calibration of most probes like blood oxygen, pH, ions, voltage, and carbon dioxide sensors. The use of optical methods to invasively measure physiological temperature has the advantage of electrical isolation, when compared to traditional approaches like the use of thermocouplers. 

Recent emission control system development in the automotive industry has been directed mainly towards the use of three-way or dual bed catalytic converters, This type of converter system not only oxidizes the hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas but will also reduce the nitrous oxides (NO ). An integral part of this type of system is the exhaust oxygen sensor which is used to provide feedback for closed loop control of the air-fuel ratio. This is necessary since this type of catalytic converter system operates efficiently only when the composition of the exhaust gas is very near the stoichiometric point. 

As mentioned earlier, the oxidation of carbon monoxide and hydrocarbons should be achieved simultaneously with the reduction of nitrogen oxides. However, the first reaction needs oxygen in excess, whereas the second one needs a mixture (fuel-oxygen) rich in fuel. The solution was found with the development of an oxygen sensor placed at exhaust emissions, which would set the air-to-fuel ratio at the desired value in real time. So, the combination of electronics and catalysis and the progress in these fields led to better control of the exhaust emissions from automotive vehicles. 

GSSs are purposefully designed electrochemical cells, a galvanic cell in the case of carbon dioxide sensors, and an electrolytic cell in the case of the oxygen sensors. 

Fig. 8.4 (a) shows the response of the oxygenate sensor-1 (Sn02 sensitized with Ti02) towards an alcohol (1-propanol), aldehyde (propanal), ketone (acetone), carbon monoxide (CO) and propane. The sensor is sensitive to the alcohol, aldehyde and ketone but not to CO and propane. Conversely, oxygenate sensor 2 (Sn02 sensitized with 13 wt% Si02/Al203) is less sensitive to the alcohol than aldehyde (Fig. 8.4b). Alcohol formation can thus be estimated from a comparison of the output signals of oxygenate sensors 1 and 2.

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]).

Luz, R. D. S., Damos, F. S., Tanaka, A. A. and Kubota, L. T. (2006), Dissolved oxygen sensor based on cobalt tetrasulphonated phthalocyanine immobilized in poly-L-lysine film onto glassy carbon electrode. Sensor Actuator B Chem., 114(2) 1019-1027. 

Kotzeva, V.P. and Kumar, R.V. (1999) The response of yttria stabilized zirconia oxygen sensors to carbon monoxide gas. Ionics, 5 (3-4), 220-6. 

The first concept is the closed-loop-controlled three-way catalyst. In this, one type of catalyst, which is placed in the exhaust gas stream, is able to promote all the main reactions that lead to the simultaneous removal of carbon monoxide, hydrocarbons and nitrogen oxides. To balance the extent of the oxidation and the reduction reactions, the composition of the engine-out exhaust gas is maintained at or around stoichiometry. This is achieved by a closed-loop engine operation control, in which the oxygen content of the engine-out exhaust gas is measured up-stream of the catalyst with an electrochemical oxygen sensor, also called lambda sensor. 

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. 

Burkhard, D.J.M., Hanson, B., and Uhner, G.C., ZrOj oxygen sensors An evaluation of behavior at temperatures as low as 300°C, Solid State Ionics 47 (1991) 169-175. Can, Z.Y. et al., Detection of carbon monoxide by using zirconia oxygen sensor, Solid State Ionics 79 (1995) 344-348. 

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. 

A carbon dioxide sensor for monitoring levels in a closed exhalation anesthesia system was developed by Jordan (23). 7,10-dioxa-3,4-diaza-l,5,12,16-hexadecatetrol was prepared by mixing monoethanolamine, often used as a CO2 scrubber, with ethylene gylcol diglycidyl ether in a 2 1 ratio and was used as a coating. The respone was 391 Hz for 10% CO2, exposure time less than 30 sec, and complete recovery in less than 60 sec. No interferences were reported from nitrous oxide, halothane, or oxygen tested at normal anesthesia concentrations. 

---