NO sensors electrodes for

WO3 has been used as an electrode for CO sensors [254—260]. Figure 13.21 [254—258] shows that the outputs of CO sensors with YSZ electrolytes and WO3 electrodes decrease with increasing temperature, which, as discussed earlier, is a general tendency for nonequilibrium sensors. Tungsten oxide has also been used as an electrode for NO sensors [246, 254—259, 261-263], some examples of which are shown in Figure 13.22 [254—259, 262, 263[. 

Recently, La2CuO4 [332-334] and (La,Sr)2CuO4 ]335] have shown promise as electrodes for NO, sensors. Tlte response of La2CuO4 is attributed to the effect of the adsorbed intermediate N-0 ionic species on the Fermi level in the electrode. This... 

The most important selectivity parameter of electrodes for voltammetric sensors is the applied potential. Ideally, the electrode potentials of the redox couples would be sufficiently far apart for there to be no interference between different species. Unfortunately this is not the case, and it is necessary to look for greater selectivity. We can discriminate better between the different species present in solution through a correct choice of conditions for the study of the electrode reaction electrode material (Chapter 7) in some cases through surface modification use of hydrodynamic electrodes (Chapter 8) application of potential sweep... 

White et al. synthesized nanometric La2Cu04 through three techniques auto-ignition, Pechini method, and coprecipitation (White et al., 2008). The NPs were used to fabricate sensing electrodes for NO, and the effect of electrode microstructure on the sensitivity and response time was studied. The response times of the sensors were exponentially dependent on electrode grain size. Sensors with fine-grained electrodes were able to produce a steady-state and consistent voltage at lower temperatures, which improved their response sensitivity. 

Zirconia electrolytes have also been used for NO, sensors by using nitrates (NaN03 [94] or Ba( O j)2 [189]) as auxiliary electrodes. As nitrates are typically less stable than carbonates and sulfates, nonequilibrium-based NO, sensor are more commonly used (these will be discussed later). 

Nickel oxide has also been used as the electrode material for NO sensors [264—274]. One of the advantages of NiO electrodes is the improved sensor response at high temperatures. Figure 13.23 shows the sensitivities of XO, sensors with WO3 [254—259, 262] or NiO [264—269] electrodes. As shown above for CO sensors, the responses of sensors vhth WO3 electrodes decrease as the temperature is increased above 600 °C. The responses of sensors with NiO electrodes, however, remain high up to operating temperatures of900 °C. The response of NiO electrodes can be increased even further with the addition of ruthenium [268]. 

Two-phase mixtures of oxides have also been used in mixed potential sensors. Such examples include Cr2O3 + NiO [297] for NO sensors, CuO + ZnO [298, 299] or SnO2 + CdO [300] for CO sensors, and In2O3 + MnO2 [301, 302] for hydrocarbon sensors. Some examples ofthe outputs of NO -and CO sensors with two-phase oxide mixtures as electrodes are shown in Figure 13.24 [270, 297, 298, 300]. 

Miura, N. et al.. Mixed potential type sensor using stabilized zirconia and ZnPe204 sensing electrode for NO detection at high temperature. Sensors and Actuators B, Chem. 81 (2002) 222-229. 

Kimura and coworkers [17], Diamond [18], and Damien et al. [19] have described that the polymeric calix-[4]arenes have been used as ionophores in ion selective electrodes for Na (based on calixarene esters and amides) and for Na and Cs (based on p-alkylcalixarene acetates). The electrodes are stated to function as poten-tiometric sensors as well, having good selectivity for primary ion, virtually no response to divalent cations, and being stable over a wide pH range. 

There is an increasing interest in the development of electrochemical sensors and microsensors for detecting and monitoring NO or N02, due to their importance in clinical and environmental analysis. It has been suggested that transition metal electrocatalysts active for NO or N02 coordination and reduction could be exploited for the development of metal-complex film electrodes for N02 and NO sensing. However, most of the sensory devices reported so... 

The first amperometric NO electrode used for direct measurement was described in 1990 [20], In 1992, the first commercial NO sensor system was developed. Over... 

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