Influence of Humidity on a Potentiometric  CO 2 Gas Sensor Using a Combined Electrolyte of Sodium Ion Conducting Glass and Stabilized Zirconia

Abstract

A CO2 gas sensor using a combined solid electrolyte of a Na conducting Na20-A1203-4SiO2 glass and an yttria-stabilized zirconia was prepared, and its sensing properties in dry and wet gases were investigated using a variable flow rate of the test gases. The glassy electrolyte in the sensor was suitable as a CO2 sensing material because of its high density and good contact between the electrolytes. In a dry atmosphere, excellent results were obtained for the CO2 gas concentration dependence of the electromotive force (EMF), expressed by EMF (mV) = 547.5 -74.0 log [C0Jppm] at 470°C in which the sensitivity of 74.0 mV/decade was in fair agreement with the theoretical value based on a two-electron electrochemical reaction. In the case of wet CO. gas, the sensitivities and response time were depressed even for a high CO2 gas concentration. The decomposition of Na2CO3 into sodium oxide on the Pt electrode was accelerated in the presence of H9O. The reason for the depression of the sensing properties in a humid condition could be ascribed to its reformation reaction as a side reaction.

Room-Temperature Hydrogen Sensors Based on an In[sup 3+]-Doped SnP[sub 2]O[sub 7] Proton Conductor

“…Similar dependence on the flow rate has been observed for many mixed-potential-type sensors. 16,22,23 Sensing characterization of single-chamber H 2 sensor.-As shown in Fig. 4, the sensitivity of the sensor strongly depended on the Pt loading amount in the working electrode.…”

Humidity Influence on the CO2Response of Potentiometric Sensors Based on NASICON Pellets with New Compositions, Na3Zr2−(x/4)Si2−xP1+xO12(x= 1.333)

“…Also, in this case, the partial formation of sodium oxides can explain the decrease in the emf. 38 This is due to the reaction between Na ϩ and O 2-ions obtained by the decomposition reactions between Na 2 CO 3 and H 2 O. In fact, the formation of NaOH and NaHCO 3 is expected by these reactions, but this leads to an increase in the emf.…”

“…6 However, NaOH can easily react with CO 2 to produce NaHCO 3 , which in turn is unstable at temperatures Ͼ270°C, and decomposes forming again Na 2 CO 3 . 38 Therefore, the partial formation of sodium oxides derives from the following reactions. The following redox equilibrium usually exists on the Na ϩ -conducting electrolyte:…”

“…To understand the reasons for the deviations from the theoretical behavior at low CO 2 concentrations and in humid environments, measurements were performed varying the gas-flow rate. 38 In fact, the relationship between the 90% response time (R) and the reciprocal of the flow rate (1/F) was very useful to evaluate the reactions occurring at the measuring electrode. 39 Figure 5 shows the relationship between R and 1/F in dry gas for the gas sensor prepared using sample C, measured at 465°C.…”

Potentiometric Cl[sub 2] Gas Sensor Using a Na[sup +] Conducting Composite NASICON-40 wt % (Na[sub 2]O-Al[sub 2]O[sub 3]-4SiO[sub 2]) Solid Electrolyte

“…1 It has been demonstrated that the use of alkali ion conductors allows the detection of SO x , NO x , and CO 2 . [2][3][4][5][6][7] The development of solid-state sensors able to measure the Cl 2 exhaust gas concentration is extremely appealing. Up to now, Ag ϩ -␤-alumina, 8 MgO-stabilized zirconia, 9 and chloride Cl Ϫ ionic conductors (such as the 0.97PbCl 2 -0.03KCl and the 0.97BaCl 2 -0.03KCl systems) [10][11][12][13][14][15] have been reported as materials for Cl 2 gas sensors.…”