Electrochemistry of Solid Electrolyte Gas Sensors

Solid ionic conductors that can be used in electrochemical cells as an electrolyte are called solid electrolytes. In such compotmds only one ion is mobile (see entry. Solid State Electrochemistry, Electrochemistry Using Solid Electrolytes). Generally, any conductor with a high ionic transference number can serve as an electrolyte. Often, the definition after Patterson is used who described solids with a transference number > 0.99 as solid electrolytes [1]. The transference number is not a fixed value. It depends on the temperature and the partial pressure of the gas involved in the chemical reaction with the mobile ion. Therefore, all solids are more or less conductors with a mixed ionic and electronic conductivity, so-called mixed conductors. For the application in sensors and fuel cells, only a window concerning temperature and partial pressure is suitable. This is also called as electrolytic domain. The phenomenon that solids exhibit a high ionic conductivity is also designed as fast ion transport. 

Yoon JW, GriUi ML, Bartolomeo ED, PoUni R, Traversa E (2001) The NO response of solid electrolyte sensors made using nano-sized LaFeOj electrodes. Sens Actuators B 76 483-488 Yoon SP, Nam SW, Kim SG, Hong SA, Hyun SH (2003) Characteristics of cathodic polarization at Pt/YSZ interface without the effect of electrode microstructure. J Power Sources 115 27-34 Yoon SP, Nam SW, Han J, Lim TH, Hong SA, Hyun SH (2004) Effect of electrode microstructure on gas-phase diffiision in solid oxide fuel cells. Solid State Ionics 166 1-11 Zhuiykov S (2007) Electrochemistry of zirconia gas sensors. CRC, Boca Raton, FL... 

Up to 1995, the year in which he became Professor emeritus, and even thereafter he was active in different fields of solid state electrochemistry (solid electrolytes, sensors, SOFC). His pioneering work encompasses contributions to solid oxide fuel cells, theoretical considerations regarding electrochemical phenomena in solid electrolyte cells, basic discoveries in solid electrolyte gas cells, and their applications as gas sensors in different branches of industry. Without any doubt, the discovery of the fuel-oxygen titration curve by means of solid electrolyte cells on which the lambda probe is based is his most memorable contribution to electrochemistry. At the Second European Solid Oxide Fuel Cell Forum, which took place in Oslo on May 1996, Prof. Dr. Hans-Heinrich Mobius was awarded the Christian Friedrich Schonbein Medal of Honor in recognition of his outstanding contributions to the fundamentals and the technology of solid electrolyte fuel cells [1]. 

ELECTROCHEMISTRY OF ZIRCONIA SOLID ELECTROLYTES AS THE BASIS FOR UNDERSTANDING ELECTROCHEMICAL GAS SENSORS... 

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... 

The second type is where the electrolyte bahaves as a classical electrolyte an takes no part in the electrochemistry. Rather it acts only as a solvent. Although these sensors have the potential for operation at lower temperatures they do rely on high current densities and high concentration of the gas in the solid phase. 

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