•Highly sensitive mixed potential type gas sensor based on YSZ and CdMoO4-SE was first developed for detection of acetone.•The device utilizing CdMoO4-SE exhibited the highest response of −133.5 mV to 100 ppm acetone at 625 °C.•The sensitivity of the fabricated sensor to acetone in the concentration range of 5–300 ppm was −84 mV/decade.•The sensor also showed good repeatability, selectivity, moisture resistance and stability.A highly sensitive mixed potential type gas sensor based on stabilized zirconia (YSZ) and CdMoO4 sensing electrode (SE) was developed and used for detection of acetone at 625 °C. By comparing the sensing performance for different devices fabricated, the sensor utilizing CdMoO4-SE exhibited the highest response value (−133.5 mV) to 100 ppm acetone at 625 °C, and even could achieve low detection limit of 500 ppb at 625 °C. The sensor attached with CdMoO4-SE displayed high sensitivity of −84 mV/decade to acetone in the range of 5–300 ppm at 625 °C. The present device also showed good repeatability, selectivity to certain deleterious gases, moisture resistance and acceptable drifts in 10 days measured period at 625 °C, demonstrating great potential for practical application in acetone sensing detection. Additionally, the sensor involving mixed potential mechanism was proposed and further clarified by polarization curve.

•The YSZ-based mixed-potential type gas sensor using CoTa2O6-SE was developed for NO2 detection at high temperature.•The device utilizing CoTa2O6-SE sintered at 1000 °C gave the highest response of 93 mV to 100 ppm NO2 at 650 °C.•The sensitivity of the fabricated sensor to NO2 in the concentration range of 5–500 ppm was 80 mV/decade.•The fabricated sensor also exhibited good selectivity, stability and slight effect of oxygen and moisture at 650 °C.A mixed-potential type NO2 sensor based on stabilized-zirconia (YSZ) solid electrolyte and novel trirutile CoTa2O6 sensing electrode (SE) prepared through the sol-gel method was developed at high temperature. The effect of CoTa2O6 sensing electrode material calcinated at different temperatures on NO2 sensing property was mainly investigated and the device attached with CoTa2O6-SE sintered at 1000 °C gave the highest response of 93 mV to 100 ppm NO2 and fast response and recovery times at 650 °C. The response of the sensor utilizing CoTa2O6-SE annealed at 1000 °C displayed segmentally linear relationship to the logarithm of NO2 concentration in the ranges of 0.5–5 ppm and 5–500 ppm, which the sensitivities were 12 and 80 mV/decade, respectively. Meanwhile, the present fabricated device also showed good reproducibility, selectivity, long-term stability and slight effect of oxygen and moisture at 650 °C. Furthermore, the mixed potential sensing mechanism proposed was discussed quantitatively and further verified by polarization curve measurement.

In this paper, a novel amperometric CO sensor using Nafion and Pt/C composite electrodes was fabricated. Three kinds of carbon materials (carbon fibers, multiwall carbon nanotubes and carbon blacks) were utilized as the supports of the sensing and reference electrodes for the CO sensors. The results revealed that the effective Pt loadings on the electrodes increased in the following order: carbon fibers (CFs) > multiwall carbon nanotubes (MWCNTs) > carbon blacks (CBs), leading to the increasing of the sensitivities toward CO in same order. In other words, the sensor using Pt/CFs as the sensing electrode (SE) showed the highest sensitivity with the value of 0.077 μA/ppm and shortest response time in the range of CO concentration from 1 to 200 ppm at room temperature. Further, a reproducible and stable response against 50 ppm CO was obtained for the sensor with Pt/CFs SE materials. Moreover, a low detection limit of 0.1 ppm for CO was also examined, suggesting that the sensor can be convenient for detecting very low traces of CO.

A well-ordered porous three-phase boundary (TPB) was prepared with a polystyrene sphere as template and examined to improve the sensitivity of yttria-stabilized zirconia (YSZ)-based mixed-potential-type NO2 sensor due to the increase of the electrochemical reaction active sites. The shape of pore array on the YSZ substrate surface can be controlled through changing the concentration of the precursor solution (Zr4+/Y3+ = 23 mol/L/4 mol/L) and treatment conditions. An ordered hemispherical array was obtained when CZr4+ = 0.2 mol/L. The processed YSZ substrates were used to fabricate the sensors, and different sensitivities caused by different morphologies were tested. The sensor with well-ordered porous TPB exhibited the highest sensitivity to NO2 with a response value of 105 mV to 100 ppm of NO2, which is approximately twice as much as the smooth one. In addition, the sensor also showed good stability and speedy response kinetics. All these enhanced sensing properties might be due to the structure and morphology of the enlarged TPB.

A high performance mixed potential type gas sensor based on stabilized zirconia (YSZ) and NiNb2O6 as sensing electrode was fabricated and used for detection of acetone at 650 °C. NiNb2O6 prepared via a facile sol–gel method and sintered at different temperatures was characterized using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The present study mainly focused on the effect of sintering temperature (800 °C, 1000 °C, 1200 °C) of NiNb2O6-SE materials on acetone sensing characteristics at 650 °C. Results indicated that the sensor using NiNb2O6-SE sintered at 1000 °C exhibited the largest sensitivity to acetone in the concentration range of 5–500 ppm at 650 °C, which the slope was −79 mV/decade. The response for the sensor attached with a NiNb2O6-SE sintered at 1000 °C to 100 ppm of acetone was approximately −113 mV. Moreover, the present sensor could detect even 500 ppb acetone with an acceptable response. The present device also displayed fast response and recovery times, good repeatability, slight sensitive effect to humidity, small drifts in 40 days measured periods, and acceptable selectivity at 650 °C. Additionally, the mixed potential mechanism was further demonstrated by polarization curve.

Mixed-potential type sensors utilizing stabilized-zirconia (YSZ) and MNb2O6 (M: Co, Zn and Ni) sensing electrodes (SEs) were fabricated and examined for NO2 detection at high temperature. For mixed potential type NO2 sensor present fabricated, the device attached with CoNb2O6-SE has been found to give the highest response at 750 °C compared with the other two devices and could detect even 0.1 ppm NO2 with an acceptable response value (5 mV). The present sensor showed fast response and recovery times to 100 ppm NO2 at 750 °C, which are 3 s and 15 s, respectively. ΔV of the sensor attached with CoNb2O6–SE exhibited segmentally linear relationship to the logarithm of NO2 concentration in the ranges of 0.1–2 ppm and 2–300 ppm, which the sensitivities were 10 and 52 mV/decade, respectively. Moreover, the present device also displayed good repeatability, good wet resistance, slight drifts in 30 days high- temperature measured period, and excellent selectivity in the presence of various interfering gases at 750 °C. Additionally, the mixed potential sensing mechanism was explained quantitatively and further demonstrated from the measurement of polarization curve.

Mixed-potential type YSZ-based sensor utilizing In2O3 as sensing electrode (SE) was fabricated and examined for detection of NO2 at 700 °C. The hierarchical In2O3 oxide material was synthesized via a facile hydrothermal process, and In2O3 sintered at different temperatures were characterized using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The present study mainly focused on the effect of sintering temperature of SE materials (800 °C, 1000 °C, 1200 °C) on NO2 sensing characteristics. As a result, the sensor attached with In2O3-SE calcined at 1000 °C exhibited the largest sensitivity to NO2, which the response to 100 ppm NO2 was as large as126 mV and excellent long-term stability for 30 days tested at 700 °C. It is noteworthy that the NO2 sensitivities for present device showed a small influence by the change of relative humidity at 700 °C. Additionally, the present devices also displayed good repeatability, the excellent sensitivity and relatively good selectivity in conjunction with various interfering gases before and after 30 days high-temperature-aging of 700 °C. It was speculated that the largest sensing performance for the sensor attached with In2O3-SE sintered at 1000 °C was contributed to the special micro-structure of the SE and the highest electrochemical catalytic activity for cathodic reaction of NO2 at the triple phase boundary (TPB).

A series of mixed potential type gas sensors using stabilized zirconia and M3V2O8 (M: Zn, Co and Ni) sensing electrode were fabricated and applied for detecting acetone at 600 °C. Among the sensors utilizing these composite oxides (Zn3V2O8, Co3V2O8 and Ni3V2O8)–SEs prepared via a facile sol–gel method, the sensor attached with Zn3V2O8–SE exhibited the highest response to acetone at 600 °C. Therefore, the present study mainly focused on acetone sensing performance for YSZ-based sensor using Zn3V2O8–SE at 600 °C. Results showed that the sensor attached with Zn3V2O8–SE could detect even 1 ppm acetone with an acceptable response. Moreover, ΔV of the sensor attached with Zn3V2O8–SE exhibited segmentally linear relationship to the logarithm of acetone concentration in the ranges of 1–10 ppm and 10–400 ppm, which the sensitivities were −16 and −56 mV/decade, respectively. The present device also displayed good repeatability, small drifts in 30 days measured period, and the excellent sensitivity and relatively good selectivity in the presence of various interfering gases before and after 30 days high-temperature-aging of 600 °C. Additionally, polarization curve was measured to further demonstrate the mixed potential mechanism.

Solid electrochemical sensors based on sodium super ionic conductor (NASICON) and spinel-type oxide CoCr2−x MnxO4 (x = 0, 1, 1.2, 1.4 and 2) sensing electrode were designed for sub-ppm H2S detection. In comparison with other spinel-type oxides, the sensor using CoCr1.2Mn0.8O4 showed the maximum response of 178 mV for 10 ppm H2S at 250 °C. The sensor displayed good stability for H2S during the testing period. Moreover, the sensor exhibited excellent selectivity toward H2S against the other interference gases, such as SO2, NO2, CH4, CO, C2H4, H2 and NH3. A sensing mechanism related to the mixed potential was proposed for the sensor based on NASICON and oxide electrodes. The effect of sintering temperature had also been investigated.

•NiCr2O4 is used as sensing electrode of NASICON-based acetone sensor.•A three-dimensional three-phase boundary was constructed.•The sensing performance was greatly improved by the three-dimensional TPB.•It shows large sensitivity of − 58 mV/decade at 375 °C.The improvement of the sensing performance for the mixed-potential-type acetone 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, NiCr2O4 was found to be the best suited for the sensing electrode. The NASICON powder was mixed with NiCr2O4 in different mass fraction (10 wt.%, 20 wt.%, 30 wt.% and 40 wt.%) to improve the length of TPB. By mixing NASICON powder into the NiCr2O4 electrode, the contact between NASICON and the sensing material existed not only at the interface between the NASICON layer and the oxide thick film, but also at the inside of the sensing electrode. As a result, a three-dimensional TPB was constructed, and showed an enhancing effect on the sensitivity of the sensor. The sensitivity of the device using NiCr2O4 electrode mixed with 30 wt.% NASICON to 5 ppm–100 ppm C3H6O vapor was − 58 mV/decade at 375 °C, which was higher than other devices (10 wt.%, 20 wt.% and 40 wt.%). It was also observed that the sensor showed a speedy response and recovery kinetics to acetone vapor.

This work focuses on the H2 sensing performance of the sensor with buried Au sensing electrode and spineltype oxide CoCrMnO4 insensitive reference electrode within sodium super ionic conductor(NASICON) film. The sensor showed the highest response to H2 gas on the insensitive material sintering at 800 °C. Compared with those of the traditional structure device, the sensitivity and selectivity of the sensor using buried sensing electrode were greatly improved, giving a response of −177 mV in 9×10−5 g/L H2, which was about 3.5 times higher than that of sensors with traditional structure. Moreover, the ΔV value of the sensing device exhibited linear relationship to the logarithm of H2 concentration and the sensitivity(slope) was −135 mV/decade. A sensing mechanism related to the mixed potential was proposed for the present sensor.

A low-cost and environmentally friendly hydrothermal route to the synthesis of hierarchical SnO2 nanostructures was described. The structure and morphology of the as-prepared product were characterized by various characterization techniques. The results revealed that these nanostructures were built from two-dimensional (2 D) nanosheets with the thicknesses of about 8 nm. Moreover, the amount of hydrochloric acid played a crucial role in the control of the final size and morphology of product. Gas sensors based on hierarchical SnO2 nanostructures were fabricated, and their gas sensing properties were tested for response to ethanol, acetone, formaldehyde, CO, toluene, H2 and H2S gases. The sensor showed excellent selectivity toward ethanol. At an ethanol concentration of 100 ppm, the response of the hierarchical SnO2 nanosheets was about 33, which was about 2.5 times higher than that of the nanoparticles. The response time of the sensor to 60 ppm ethanol was shorter than 11 s at the optimal operating temperature of 275 °C. The enhancement in gas sensing properties was attributed to their unique structures.

In this article, the NO2 sensing performance of the mixed-potential-type yttria stabilized zirconia (YSZ)-based sensor was improved by modifying the three-phase boundary (TPB). The double-tape casting and the pore-forming method were simultaneously used to obtain the porous YSZ-substrate. Furthermore, a group of tape-casting slurries with different starch concentrations (0 wt%, 5 wt%, 10 wt% and 15 wt%) were applied to form the different contact areas of the three-phase boundary (TPB). The scanning electron microscope (SEM) images showed that YSZ-substrate prepared by using the slurry with 15 wt% starch had the largest contact area. The sensor based on the YSZ-substrate with the largest contact areas and the MnCr2O4 sensing electrode (SE) showed the largest response compared with the other sensors when they were exposed to 10–500 ppm NO2 at 800 °C. The measured polarization (I–V) curves indicated that the present sensors operated under the mixed-potential mechanism. In addition, the sensor showed a good selectivity and repeatability to NO2.

Monodisperse α-Fe2O3 discoid crystals have been prepared through a hexamethylenetetramine (HMT)-assisted hydrothermal process combined with subsequent acid-dissolution. First, uniform α-Fe2O3 round-edged hexahedrons with a size of about 1.2 μm were synthesized. Subsequently, by a controlled acid etching process, the as-obtained α-Fe2O3 uniform hexahedrons could be facilely transformed into monodisperse α-Fe2O3 discoid crystals, without influencing the original crystal phase. Both field emission scanning electron microscope results and transmission electron microscope results revealed that the “discuses” were made of piled up nanoparticles. The selected area electron diffraction pattern from the whole discoid crystal displayed that all the nanoparticles were highly oriented, which resulted in the single-crystal “discus” features. To demonstrate the usage of such α-Fe2O3 discoid crystals, the obtained sample was applied to fabricate a gas sensor which was then tested for sensitivity to three kinds of gases (ethanol, methanol and acetone). The results of the test showed that the sensor had a high level of response and good recovery characteristics towards ethanol at the operating temperature of 238 °C.

A series of tungstate MWO4 (M = Co, Zn and Ni) has been prepared by the polymeric precursor method. Meanwhile, yttria stabilized-zirconia (YSZ) based sensors using these oxides as sensing electrodes were investigated, and among the oxides tested, CoWO4 was found to be the most suitable for the sensing electrode (SE) of the ammonia sensor. The sensor attached with CoWO4 shows the fast response and recovery characteristics (not more than 5 s respectively) and large sensitivity (− 51 mV/decade) at elevated temperature. The electric potential difference (∆V) of the sensor varies almost linearly with the NH3 concentrations in the examined range of 50–1000 ppm. The SEM observation reveals that the special microstructure of CoWO4-SE, bulky rod-like crystals coated by tiny particles, plays a significant role in sensing performance.Highlights► Rodlike CoWO4 crystal is prepared by polymeric precursor method. ► It is used as sensing electrode of NH3 sensor base YSZ electrolyte. ► It shows fast response and recovery either of which is less than 5s. ► It shows large sensitivity of –51 mV/decade at high temperature.

In this article, the NO2 sensing performance of the mixed-potential-type yttria stabilized zirconia (YSZ)-based sensor was improved by modifying the three-phase boundary (TPB). The double-tape casting and the pore-forming method were simultaneously used to obtain the porous YSZ-substrate. Furthermore, a group of tape-casting slurries with different starch concentrations (0 wt%, 5 wt%, 10 wt% and 15 wt%) were applied to form the different contact areas of the three-phase boundary (TPB). The scanning electron microscope (SEM) images showed that YSZ-substrate prepared by using the slurry with 15 wt% starch had the largest contact area. The sensor based on the YSZ-substrate with the largest contact areas and the MnCr2O4 sensing electrode (SE) showed the largest response compared with the other sensors when they were exposed to 10–500 ppm NO2 at 800 °C. The measured polarization (I–V) curves indicated that the present sensors operated under the mixed-potential mechanism. In addition, the sensor showed a good selectivity and repeatability to NO2.