Nanocomposites in Electrochemical Sensors
Present chapter shows that the design of solid state and polymer-based electrochemical gas sensors are the field of nanocomposites application. Usually almost all elements of electrochemical sensors such as solid electrolytes, sensing and auxiliary electr
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Nanocomposites in Electrochemical Sensors
16.1
Solid Electrolyte-Based Electrochemical Sensors
Electrochemical gas sensors represent another field for nanocomposites application. Moreover, it should be stated that almost all solid electrolyte sensors have been designed based on composites. For example, YSZ (ZrO2–Y2O5), NASICOM (Na3Zr2Si2PO12), and Na-β-alumina (Na2O–Al2O3 system), the main sensing materials in solid electrolyte gas sensors, can be considered as composites, which have high ionic conductivity due to their specific composition (Nakayama and Sadaoka 1994). Gd0.7Ca0.3CoO3−δ (GCC) and Ce0.8Gd0.2O1.9 (CGO) (Nigge et al. 2002) tested as oxygen-permeable membranes in an amperometric sensor for NOx detection in exhaust gases, A0.7E0.3MnO3 (A=Gd, Y, and Pr and E=Ca and Sr) (Wiemhofer et al. 2002) used for oxygen sensors, and BiCuVOx (Bi2Cu0.1V0.9O5.35; oxygen-ion conductor) fitted with perovskite-type oxide (La0.6Sr0.4Co0.8Fe0.2O3; mixed electro and ionic conductor) for fabrication mixed-potential-type gas sensors of volatile organic compounds (Kida et al. 2009) are composites as well. Kida et al. (2009) showed that La0.6Sr0.4Co0.8Fe0.2O3 and BiCuVOx composite materials have good stability against humidity and CO2. The high ionic conductivity, enhanced mechanical strength, and extensive possibilities of object-oriented control of the electrolyte properties through varying the conductance type and dopant concentration are advantages which make solid electrolyte composites very good candidates for application in electrochemical gas sensors. It is important that more complicated ZrO2-based composites have better performance than mono- or two-phase ones, including electrical, electrochemical, and mechanical properties and thermal stability, and therefore they can be used for fabricating oxygen sensors designed for operation at temperatures up to 1,600 °C, needed, for example, during steel production for controlling the level of oxygen dissolved in the melt (Fray 1996; Liu 1996). At present commercial oxygen sensors intended for application in this temperature range are usually based on magnesia-partially stabilized zirconia (Mg-PSZ) electrolytes. The main reason for using Mg-PSZ solid electrolytes in commercial oxygen sensors, besides their high emf signal, is their high thermal shock resistance. However, in the range of low oxygen potentials (
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