Research Of Deleterious Gas Sensors Based On NASICON And Oxide Electrode

The deleterious gas is a serious threat to human health when emitting into air.Therefore, high performance gas sensor is urgently desired for exactly detectingdeleterious gases in the atmosphere.For design high performance gas sensor, new sensing materials were explored andsensor structure was ameliroated. On the one hand, spinel-type oxides sensing materialshave been prepared, and influences of sintering temperature and aging treatment on theproperties of electrode materials have been discussed; On the other hand, the traditionaldevice structure has been improved, and the three-dimensional three-phase boundaryhas been constructed for further improve the sensor performances.(I) NASICON-based gas sensors attached with Cr-based spinel-type oxide (ACr2O4,A=Zn, Co, Ni) sensing electrode were fabricated, and their gas sensing properties weretested for response to chlorine (Cl2). In comparison with other spinel-type oxides,CoCr2O4-based sensor showed the maximum response to Cl2at300°C, giving aresponse of-226mV to1ppm of Cl2, which was about3.3and1.3times higher thanthat of sensors-based on ZnCr2O4and NiCr2O4, respectively. Moreover, the sensorexhibited excellent selectivity toward Cl2against the other interference gases, such asCO, NO, NO2, H2, C7H8, NH3and CH4. Interestingly, the performance of sensor couldbe markedly improved after aging at300°C for60days. Combined with the analysis byX-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and BET, apossible mechanism for the influence of aging on the Cl2-sensing properties of sensorwas proposed.(II) The improvement of the sensing performance for the mixed-potential-typeacetone sensor using NASICON and Cr-based spinel-type oxide (ACr2O4, A=Zn, Co, Ni) sensing electrode was examined by increasing the length of three-phase boundary(TPB). Among the spinel-type oxides tested, NiCr2O4was found to be the best suitedfor the sensing electrode. The NASICON powder was mixed with NiCr2O4in differentmass fraction (10wt%,20wt%,30wt%and40wt%) to improvethe length of TPB. Bymixing NASICON powder into the NiCr2O4electrode, the contact between NASICONand the sensing material not only existed at the interface between the NASICON layerand the oxide thick film, but also the inside of the sensing electrode. As a result, a three-dimensional TPB was constructed, and showed an enhancing effect on the sensitivityof the sensor. The sensitivity of the device using NiCr2O4electrode mixed with30wt%NASICON to5ppm-100ppm C3H6O vapor was-58mV/decade at375°C, which washigher than other devices (10wt%,20wt%and40wt%). It was also observed that thesensor showed a speedy response and recovery kinetics to acetone vapor.(III) Solid electrochemical sensors based on NASICON and spinel-type oxideCoCrxMn2-xO4(x=0,1,1.2,1.4and2) sensing electrode were designed for sub-ppmH2S detection. In comparison with other spinel-type oxides, CoCr1.2Mn0.8O4sintered at800°C was confirmed to be the best suited for the sensing electrode. The device attachedwith CoCr1.2Mn0.8O4showed excellent sensing characteristics to0.1-20ppm H2S in airat250°C. The90%response and recovery times to100ppb H2S at250°C were all lessthan100s for the CoCr1.2Mn0.8O4-attached device. The ΔV value of the device wasalmost linear to the logarithm of H2S concentration and the slope between ΔV and thelogarithm of H2S concentration was75mV/decade. The sensor exhibited good stabilityduring the testing period. Moreover, the sensor exhibited excellent selectivity towardH2S against the other interference gases, such as SO2, NO2, CH4, CO, C2H4, H2andNH3. The sensing mechanism related to the mixed potential could explain the sensingbehaviour of the sensor. Therefore, the sensor exhibits great applicable value fordetecting hydrothion in the atmosphere based on its excellent sensing performances.(IV) The H2sensor with buried electrode structure was designed, which consistedof Au sensing electrode and spinel-type oxide CoCrMnO4insensitive referenceelectrode on NASICON film. The sensor showed the highest response to H2gas on the insensitive material sintering at800°C. Compared with those of the traditional structuredevice, the sensitivity and selectivity of the sensor using buried sensing electrode weregreatly improved, giving a response of-177mV in1000ppm H2, which was about3.5times higher than that of sensors with traditional structure. Moreover, the ΔV value ofthe sensing device exhibited linear relationship to the logarithm of H2concentration andthe sensitivity (slope) was-135mV/decade. A sensing mechanism related to the mixedpotential was proposed for the present sensor.