Yongtie Yan

Sensing characteristics and mechanisms of hydrogen sulfide sensor using stabilized zirconia and oxide sensing electrode

A new type of electrochemical sensors for H2S was developed by combining a Y 2 O 3 -stabilized zirconia (YSZ) tube with a sensing oxide layer of WO 3 . The sensor device composed was an electrochemical cell of the form, air, Pt|YSZ|WO 3 , Pt, H 2 S (+air). This device was found to respond well to 0.2-25 ppm H2S in air at 400°C, with acceptable response rates. The EMF of the sensor was linearly related to the logarithm of the H2S concentration with a slope of -74 mV/decade. In addition, the EMF was hardly affected by the coexistence of CO 2 and water vapor. Based on the measurements of anodic and cathodic polarization curves, the H 2 S sensing signal was suggested to reflect the mixed potential at the zirconia/WO 3 interface. The possibility of amperometric detection by using the present device was also suggested.

Stabilized zirconia-based NOx sensor operative at high temperature

Abstract An electrochemical device combining an MgO-stabilized zirconia (MSZ) tube with an auxiliary phase of Ba(NO 3 ) 2 was found to exhibit fairly good Nernsts response to dilute NO 2 in air at elevated temperature (450 °C). The response to NO in air could be improved to be roughly comparable to that to NO 2 when Ba(NO 3 ) 2 was added with 10 mol% CaCO 3 . The EMF response of the tubular device to a fixed concentration of NO 2 or NO was strongly dependent on O 2 concentration. The effect of O 2 was much mitigated with a probe-type planar device.

Solid-state potentiometric CO2 sensors using anion conductor and metal carbonate

Abstract Solid-state potentiometric CO 2 sensors have been fabricated by combining a fluoride-ion conductor (LaF 3 ) or an oxide-ion conductor (stabilized zirconia) with an auxiliary phase of a metal carbonate (Li 2 CO 3 ). The e.m.f. response of the LaF 3 -based sensor fitted with Li 2 CO 3 is found to follow Nernsts equation for the two-electron reaction of CO 2 in the concentration range 40–2000 ppm at 400 and 450 °C. The 90% response times are as short as 10–20 s at 400 °C. The tubular-type MgO-stabilized zirconia (MSZ) sensor fitted with Li 2 CO 3 also responds well to CO 2 , giving the same Nernstian behaviour as above at 500–650 °C. The CO 2 sensitivity of this sensor is hardly affected by coexistent NO, NO 2 or H 2 O, and is rather stable for the test period of ≈ 2800 h. Furthermore, it is possible to design a planar-type MSZ sensor that is insensitive to O 2 and gives a stable e.m.f. response to CO 2 regardless of variations in O 2 concentration. The CO 2 sensing mechanisms of these new type sensors are discussed.

Characteristics and sensing mechanism of SOx sensor using stabilized zirconia and metal sulphate

Abstract Solid-state electrochemical SO 2 sensors have been developed by using an MgO-stabilized zirconia tube coated with metal sulphates, such as Li 2 SO 4 , Na 2 SO 4 , Li 2 SO 4 -CaSO 4 , and Li 2 SO 4 -CaSO 4 -SiO 2 . The sensors exhibit fairly good sensing properties for 10–200 ppm SO 2 in air at 600–800 °C, with their e.m.f. responses following Nernsts equation for the two-electron reduction of SO 2 . The response rates can be improved by the use of binary sulphates: Li 2 SO 4 -CaSO 4 (6:4 in molar ratio) gives 90% response and 90% recovery times of 12 s and 2.5 min, respectively, for 130 ppm SO 2 at 800 °C. The response is found to be further improved with the ternary system Li 2 SO 4 -CaSO 4 -SiO 2 (4:4:2 in molar ratio).

Sensing properties and mechanism of a planar carbon dioxide sensor using magnesia-stabilized zirconia and lithium carbonate auxiliary phase

A planar electrochemical device using MgO-stabilized zirconia (MSZ) and Li2CO3 has been fabricated for potentiometric sensing of CO2. The emf response of the device to CO2 followed the Nernst equation well in the concentration range 100–2000 µl l–1 at 500–650 °C, and was kept unchanged with a variation in the concentration of coexistent O2, NO, NO2, H2 or H2O. The rates of response and recovery were fairly rapid, attaining 90% of the changes in 10 s and 2 min, respectively, for 100–1000 µl l–1 CO2 at 550–600 °C. The electrochemical chain as well as the emf response to CO2 of the novel device can be explained by considering the formation of Li2ZrO3 between MSZ (O2– conductor) and Li2CO3(Li+ conductor) as an ‘ionic bridge’.

High-performance solid-electrolyte SOx sensor using MgO-stabilized zirconia tube and Li2SO4CaSO4SiO2 auxiliary phase

Abstract Solid-electrolyte-based electrochemical SO x sensors fabricated with MgO-stabilized zirconia and Li 2 SO 4 CaSO 4 SiO 2 (4:4:2 in molar ratio) exhibit fairly good sensing characteristics for 2–200 ppm SO 2 in air at 600–750 °C, with the e.m.f. responses following the Nernst equation for the two-electron reduction of SO 2 . The 90% response and 90% recovery times to 20 ppm SO 2 are 10 s and 7 min at 650 °C, and 10 s and 3 min at 700 °C, respectively. It is further found that the sensor exhibits excellent selectivity to SO x in the coexistence of CO 2 and NO x , and good long-term stability. The sensor is simple in structure, easy to prepare, and quite tough chemically and mechanically. These features should ensure practical use for this SO x sensor.

Potentiometric sensor using stabilized zirconia for chlorine gas

A new type of solid-electrolyte gas sensor for chlorine in an O 2 -containing atmosphere has been fabricated by combining an MgO-stabilized zirconia tube with an auxiliary phase containing metal chloride. The sensor gives fairly good sensing characteristics to 1-100 ppm Cl 2 at 550-650 °C, with the e.m.f. response changing linearly with a change in the logarithm of the Cl 2 concentration. With a multicomponent auxiliary phase of BaCl 2 -KCI-MgO, the times for 90% response and 90% recovery on switching between 4 and 40 ppm Cl 2 at 550 °C are 6 s and 2 min, respectively. The e.m.f. response to Cl 2 is hardly influenced by coexistent CO 2 , while it shifts significantly in the presence of water vapour.

Total-NOx Sensor Based on Mixed-Potential for Detecting of Low NOx Concentrations

We have been developing the mixed-potential type NOx sensor which can detect the total-NO x concentration directly in exhausts for automobiles. It has been confirmed that the sensor is capable of detecting wide concentrations of total-NOx from 20 to 1000 ppm under the condition from rich-burn (A/F=12) to lean-burn without any interference from reducing gases, such as HC and CO. In addition, it has been confirmed that the sensor output is correlated fairly well to NOx concentrations from the analyzer in the engine test at any rotations. The results obtained here indicate that the present sensor has great possibility of being utilized as an on-board NOx sensor for practical use.