Oxygen sensors electrode

Oxygen sensor electrodes can experience temperatures as high as OdO C during cell preparation because of the necessity to remove organic impurities in the... 

Application The zirconia oxygen sensor is widely used for combustion control processes and for air/fuel ratio regulation in internal combustion engines. The closed-end portion of the electrode tube is inserted into the exhaust gas stream. In the control of industrial combustion processes, no out stack sampling system is required. 

When a solid electrolyte component is interfaced with two electronically conducting (e.g. metal) films (electrodes) a solid electrolyte galvanic cell is formed (Fig. 3.3). Cells of this type with YSZ solid electrolyte are used as oxygen sensors.8 The potential difference U R that develops spontaneously between the two electrodes (W and R designate working and reference electrode, respectively) is given by ... 

T. Arakawa, A. Saito, and J. Shiokawa, Surface study of a Ag electrode on a solid electrolyte used as oxygen sensor, Applications of Surface Science 16, 365-372 (1983). 

The principle of antioxidant detection is shown in Fig. 17.3. Superoxide was enzymatically produced and dismutated spontaneously to oxygen and H202. Under controlled conditions of superoxide generation such as air saturation of the buffer, optimal hypoxanthine concentration (100 pM) and XOD activity (50mU ml-1) a steady-state superoxide level could be obtained for several min (580-680 s). Since these steady-state superoxide concentrations can be detected by the cyt c-modified gold electrode, the antioxidate activity can be quantified from the response of the sensor electrode by the percentage of the current decrease. 

In general Zr02 oxygen sensors consist of a tube-like solid-state Zr02 electrolyte where the electronic conductivity is based on oxygen ion charge carrier transport. The inner and outer surface of the yttrium-doped and stabilized zirconia tube is covered by porous platinum electrodes. 

Table 6.1 Comparison between fibre-optic oxygen sensors and commercial electrode sensors.

Fibre-optic oxygen sensor systems Commercial electrodes... 

Figure 13.10 shows the calibration curve of the LED-based optical oxygen sensor compared with the calibration curve of a commercially available Clark-type sensor (Ingold Electrodes, Wilmington, Massachusetts). While the Clark-type shows a linear calibration, the optical sensor allows a hyperbolic response as predicted by the Stem-Volmer-type equation 72 ... 

L. C. Clark first suggested in 1956 that the test solution be separated from an amperometric oxygen sensor by a hydrophobic porous membrane, permeable only for gases (for a review of the Clark electrode see [88]). The first potentiometric sensor of this type was the Severinghaus CO2 electrode [150], with a glass electrode placed in a dilute solution of sodium hydrogenocarbonate as the internal sensor (see fig. 4.10). As an equilibrium pressure of CO2, corresponding to the CO2 concentration in the test solution, is established in the... 

BaSn03/SiC device also has the potential to be used as an oxygen sensor without the need for a reference electrode and reference air. 

While a number of designs have been used, most oxygen sensors for automotive applications consist of a hollow, closed end tube, a schematic of which is shown in Figure 2. As shown, the interior of the closed end tube is open to the atmosphere which serves as a constant or reference oxygen partial pressure while the exterior is exposed to the exhaust gas. The voltage signal produced by the electrolyte is sensed by electrodes on the inner and outer surface of the sensor. These, in turn, are connected to the electronics package of the closed loop system. 

The electrodes and electrode protective coating of the oxygen sensor play a crucial role in determining the performance characteristics and durability (2). The electrodes used are the inner or air-reference electrode and the outer or exhaust gas electrode. The protective coating goes over the outer or exhaust electrode. While a complete discussion of the requirements and properties of the electrodes and electrode protective coating is beyond the scope of this paper, a brief description will be given. 

The history of electrochemical sensors began in the thirties of the twentieth century, when the pH-sensitive glass electrode was deployed, but no noteworthy development was carried out till the middle of that century. In 1956, Clark invented his oxygen-sensor based on a Ft electrode in 1959, the first piezoelectric mass-deposition sensor (a quartz crystal microbal-ance) was produced. In the sixties, the first biosensors (Clark and Lyons, 1962) and the first metal oxide semiconductor-based gas sensors (Taguchi, 1962) started to appear. 

Mari suggests using oxides as electrode materials33 in oxygen sensors because... 

A major advance in the performance of amperometric oxygen sensors has been achieved by placing both the cathode and the anode behind the oxygen-permeable membrane (Fig. 7.4). This sensor is known as the Clark oxygen electrode. 

Yttrium stabilized zirconia (Zr02-Y203) as an electrolyte for reduction of molecular oxygen at elevated temperatures (400-800°C) has been already discussed in Section 6.23.4. In fact, both the reduction of oxygen and the oxidation of the oxide ion at the Pt/zirconia interface is reversible and the transport of both species in zirconia is so rapid it is possible to construct an electrochemical oxygen pump, which is the heart of the limiting current oxygen sensor described in this chapter (Saji, 1987). The overall electrochemical reaction that takes place at the porous Pt electrode is... 

The idea of separating the gas sample by a gas-permeable membrane from the actual internal sensing element is common to several types of electrochemical and some optical sensors. The potentiometric Severinghaus electrode and the amperometric oxygen Clark electrode have already been discussed. Actually, most types of sensors can be used in this configuration and the conductometric sensor is not an exception (Bruckenstein and Symanski, 1986). 

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