Solid-electrolyte gas sensors

Since the doped Zr02 solid electrolyte (an oxygen ion conductor) oxygen gas sensors were successfully applied in the exhaust system of almost all modern automobiles in the mid-1990s, the other gases CO, NO, and short-chain hydrocarbons have been paid attention to closely [67]. Solid electrolyte gas sensors based on potentiometric have various configurations. Three types have been classified by Weppner, depending on whether the ionic species derived from the gas in question coincides with the mobile ion (Type I), the immobile ion (Type II), or neither of them (Type III) of the solid electrolyte used [68]. 

FIGURE 1.1 Three types of solid electrolyte gas sensors (AP Auxiliary phase, Type III for CO2 sensor using NASICON/NajCOj). (Reprinted from IEEE Sensors J., 1, Lee D.-D et ah. Environmental gas sensors, 2001, with permission from Elsevier.) 

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Jasinski, G., Jasinski, P.. Nowakowski. A. and Chachulski, B. (2006) Properties of a lithium solid electrolyte gas sensor based on reaction kinetics. Meas. Sci. Technoi.. 17, 17-21. 

Hyodo, T., Tadashi, T, Kumazawa, S., Shimizu, Y. and Egashira, M. (2007) Effects of electrode materials on CO2 sensing properties of solid-electrolyte gas sensors. Sens. Mater, 19 (6), 365-76. 

Zosel, J. and Guth, U. (2004) Electrochemical solid electrolyte gas sensors-hydrocarbon and NOx analysis in exhaust gases. Ionics, 105 (5-6), 366—77. 

Consequently, the proposed model allows the necessary information regarding the electrolyte-metal electrode interface and about the character of the electronic conductivity in solid electrolytes to be obtained. To an extent, this is additionally reflected by the broad range of theoretical studies currently published in the scientific media and is inconsistent with some of the research outcomes relative to both physical chemistry of phenomena on the electrolyte-electrode interfaces and their structures. Partially, this is due to relative simplifications of the models, which do not take into account multidimensional effects, convective transport within interfaces, and thermal diffusion owing to the temperature gradients. An opportunity may exist in the further development of a number of the specific mathematical and numerical models of solid electrolyte gas sensors matched to their specific applications however, this must be balanced with the resistance of sensor manufacturers to carry out numerous numbers of tests for verification and validation of these models in addition to the technological improvements. 

FIGURE 2.1 Summarized structural scheme of measuring transformations in the solid electrolyte gas sensors. (Reprinted from Zhuiykov, S., Mathematical modelling of YSZ-based potentiometric gas sensors with oxide sensing electrodes part II Complete and numerical models for analysis of sensor characteristics, Sensors and Actuators B, Chem. 120 (2007) 645-656, with permission from Elsevier Science.)... 

The comprehensive analysis of physical, chemical, and electrochemical processes occurring in the solid electrolyte gas sensors, allows verifying the adequacy of mathematical models to the real gas sensors. Processing the results of multiple experimental measurements of the gas sensors consists in elucidation of the type of experimental data distribution, evaluation of the parameters of the established distribution, and verification of the adequacy of the mathematical model to the real sensor. 

Conditions for Determination of Equilibrium Cell Potential Differences of Solid Electrolyte Gas Sensors... 

Figure 25-29. Signals from a hot solid-electrolyte gas sensor as a detector behind a gas-chromatographic column analyzing two portions of technical carbon monoxide. The carrier gas was nitrogen with a very small oxygen concentration [85]. In the first run the sample was mixed with air.

Numbers of detectable gases have been increased since Gauthier et al.[3] first proposed the feasibility of solid electrolyte gas sensors for SOj, NOj, CO and so on. Moreover the couple of a metal oxide solid electrolyte and an auxiliary electrode, investigated recently, makes it possible for stable operation and disuse of a reference gas. Electrochemical gas sensors has a strong point of detecting gases selectively because only one kind of ion can permeate through... 

Electrochemical, such as ion-selective electrodes (ISE), ion-selective field affects transistors (ISEET), solid electrolyte gas sensors, semiconductor-based gas sensors, and conducting polymer sensors. Most electrochemical sensors are based on potentiometry, voltammetry, or amperometry although coulometry and conductimetry have also been utilized. 

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