Solid electrolyte chemical sensors oxygen

Fig. 9.13 Typical configurations of potentiometric oxygen sensors with yttria-stabilized zirconia solid electrolyte, where the oxygen chemical potential over porous metallic reference electrode is fixed by supplying a gas mixture of known composition (a) and where a solid-state RE is used (b)...

Electrochemical Microsensors. The most successful chemical microsensor in use as of the mid-1990s is the oxygen sensor found in the exhaust system of almost all modem automobiles (see Exhaust CONTROL, automotive). It is an electrochemical sensor that uses a solid electrolyte, often doped Zr02, as an oxygen ion conductor. The sensor exemplifies many of the properties considered desirable for all chemical microsensors. It works in a... 

Micromachined and microfabricated electrochemical sensors have been used either per se, or as part of a sensor system, in many practical applications. This includes various biosensors and chemical sensors reported in research literature. An example of a practical electrochemical sensor is the yttria-stabilized zirconium dioxide potentiometric oxygen sensor used for fuel-air control in the automotive industry. Thick-film metallization is used in the manufacture of this sensor. Even though the sensor is not microsize, this solid electrolyte oxygen sensor has proven to be reliable in a relatively hostile environment. It is reasonable to anticipate that a smaller sensor based on the same potentiometric or the voltammetric principle can be developed using advanced microfabrication and micromachining techniques. 

Rbder-Roith, U., Rettig, R., Roder, T, Janek, X, Moos, R. and Sahner, K. (2009), Thick-flhn solid electrolyte oxygen sensors using the direct ionic thermoelectric effect. Sensors and Actuators B Chemical, 136(2), 530-5. 

Somov, S. I. and Guth, U. (1998), A parallel analysis of oxygen and combustibles in solid electrolyte amperometric cells, Sensors and Actuators B Chemical, 4il, 131-8. 

Electrochemistry plays an important role in the large domain of. sensors, especially for gas analysis, that turn the chemical concentration of a gas component into an electrical signal. The longest-established sensors of this kind depend on superionic conductors, notably stabilised zirconia. The most important is probably the oxygen sensor used for analysing automobile exhaust gases (Figure 11.10). The space on one side of a solid-oxide electrolyte is filled with the gas to be analysed, the other side... 

Many oxygen ion conducting electrolytes are available for sensor applications. These include mainly solid solutions of Zr02, HFO, Th02, or CeO. Of these, stabilized zirconia has been found to have the best combination of cost, mechanical, chemical, and electrical properties for this type of application and has been the most widely used. Various stabilizers are available and have a strong effect on the properties obtained, particularly the electrical conductivity. 

For the solid-state RE, the reference chemical potential is established by a mixture of two compounds whose equilibrium involves electrochemically active species, similar to the buffer solutions enabling fixing pH in the electrochemistry of aqueous electrolytes. In the case of oxygen sensors, these mixtures comprise... 

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