Mixed-potential sensors fabrication

One of the advantages of mixed potential sensors is that it is possible for both electrodes to be exposed to the same gas. The elimination of a need to separate the two electrodes simplifies the sensor design, which in turn reduces fabrication costs. Although this simpler planar design is often used, the electrodes are sometimes separated to provide a more stable reference potential. As with equilibrium potentiometric sensors, the minimum operating temperature is often limited by electrolyte conductivity. However, the maximum operation temperatures for nonequilibrium sensors are typically lower than those of equilibrium sensors, because the electrode reactions tend towards equilibrium as the temperature increases. This operating temperature window depends on the electrode materials, as will be discussed later in the chapter. 

Consequently, it can be concluded that the enhancement of the NO2 sensitivity and selectivity for the zirconia mixed-potential sensors with the oxide-SE will be focused on the technological improvements in fabrication of the SE. Eurther development of the sintering technology for the SE will be based on predicted calculation of how the initial binary oxide mixtures will be transferred into solid solutions with domination of one oxide phase and trace of another. In these solid solutions, the electrode kinetic of the bulk reactions within the SE will be responsible for sensitivity and selectivity of the sensor. 

This section analyzes electrochemical sensors for CO2 detection. The two main categories of electrochemical sensing principles are reviewed (amper-ometric and potentiometric) and among potentiometric sensors, special attention is given to mixed potential sensors, because carbon monoxide sensors belong to this group. The influence of the materials and fabrication processes in the sensor performance is also evaluated. 

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