Double perovskite La2CoMnO6 hollow spheres prepared by template impregnation for high-performance supercapacitors

Xylene is a toxic carcinogen, which may irritate eyes and respiratory tract, or damage the central nervous system. However, the traditional semiconductor gas sensor can only detect the ppm level of xylene gas, which cannot meet the building air quality monitoring requirements. Therefore, the development of low concentration gas detection of xylene gas sensor is necessary. In this article, a one-step hydrothermal method for the preparation of reduced graphene oxide (rGO)/Co3O4 nanocomposite was reported. Then, rGO/Co3O4 nanocomposites were characterized by various characterization methods. It was found that the structure of cobalt tetroxide (Co3O4) nanoparticle-coated rGO nanosheets was successfully synthesized. Specific internal morphology could be seen by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Then the gas sensor made of rGO/Co3O4 nanocomposite material was tested for its gas sensitivity performance. A series of properties such as repeatability and stability of the material were tested. According to the test results, the sensitivity of 1rGO/Co3O4 (3.35 wt%) to xylene gas was better than that of 2rGO/Co3O4 (5.54 wt%) and pure Co3O4, and the optimal working temperature of rGO/Co3O4 to 50 ppm xylene was 175 °C, which was 50 °C lower than that of pure Co3O4. In addition, the rGO/Co3O4 gas sensor could also detect xylene gas with a minimum concentration of 1 ppb. Finally, the gas sensing mechanism of the gas sensor for xylene gas was analyzed.

Ppb-Level Xylene Gas Sensors Based on Co 3 O 4 Nanoparticle-Coated Reduced Graphene Oxide(rGO) Nanosheets Operating at Low Temperature

YSZ-based potentiometric sensors employing thin CeO2-added Au sensing electrodes (SEs) were fabricated by using a spin-coating method, and effects of the CeO2 addition on their toluene sensing properties were examined. The sensor response (ΔE) to 50 ppm toluene of the sensors using 8 wt% CeO2-added Au SEs tended to decrease with an increase in the number of spin-coating cycles (x: 5, 10, 15; i.e., the thickness of SEs). However, ΔE of the sensors using 24 wt% CeO2-added Au SEs showed an opposite behavior to what was observed for 8 wt% CeO2-added Au SEs. The sensor using the thickest SE (x: 15) showed the largest ΔE (e.g., ca. 212 mV for 50 ppm toluene) at 450 °C among all the sensors examined and responded even to 0.5 ppm toluene. ΔE exponentially increased with an increase in logarithmic toluene concentration in the range higher than 10 ppm. These obtained results indicate that electrochemical toluene oxidation proceeds at triple-phase boundaries in SE with gas (Au/CeO2/gas) in addition to conventional TPBs (SE/YSZ/gas) in addition to the conventional interface at SE/YSZ/gas, because CeO2 is a mixed ionic and electronic conductor. The electrochemical reactions at TPBs of the sensor were also discussed on the basis of the I–E characteristics and the electrochemical impedance properties. 

Improved Toluene Response of Mixed-Potential Type YSZ-Based Gas Sensors Using CeO2-Added Au Electrodes

NiWO4 microflowers with a large surface area up to 79.77 m2·g-1 are synthesized in situ via a facile coprecipitation method. The NiWO4 microflowers are further decorated with multi-walled carbon nanotubes (MWCNTs) and assembled to form composites for NH3 detection. The as-fabricated composite exhibits an excellent NH3 sensing response/recovery time (53 s/177 s) at a temperature of 460 °C, which is a 10-fold enhancement compared to that of pristine NiWO4. It also demonstrates a low detection limit of 50 ppm; the improved sensing performance is attributed to the porous structure of the material, the large specific surface area, and the p-n heterojunction formed between the MWNTs and NiWO4. The gas sensitivity of the sensor based on daisy-like NiWO4/MWCNTs shows that the sensor based on 10 mol % (MWN10) has the best gas sensitivity, with a sensitivity of 13.07 to 50 ppm NH3 at room temperature and a detection lower limit of 20 ppm. NH3, CO2, NO2, SO2, CO, and CH4 are used as typical target gases to construct the NiWO4/MWCNTs gas-sensitive material and study the research method combining density functional theory calculations and experiments. By calculating the morphology and structure of the gas-sensitive material NiWO4(110), the MWCNT load samples, the vacancy defects, and the influence law and internal mechanism of gas sensitivity were described.

NiWO 4 Microflowers on Multi-Walled Carbon Nanotubes for High-Performance NH 3 Detection

Rational construction of two-dimensional (2D) metal-organic frameworks (MOFs) nanomaterials attracts researcher’s much attention due to their unique structural merits. Herein, 2D spindle-like pure and Sn-doped Co3O4 porous nanosheets have been synthesized using 1, 4-dicarboxybenzene (H2BDC) as a ligand acid, and via a simple solvothermal method and following thermal treatment. The structure, morphology and composition of the as-obtained samples are characterized by XRD, FESEM, TEM, XPS, ICP, AFM, UV–vis-NIR, UPS and nitrogen adsorption-desorption measurement. The results show that Sn4+ has been successfully doped into the lattice of Co3O4. The gas sensing properties of pure and Sn-doped Co3O4 porous nanosheets have been systematically analyzed. The 5 at% Sn-doped Co3O4 sample shows high responses of 70.7–100 ppm triethylamine (TEA) at a relatively low working temperature of 180 °C, which are about 11 times than that of pure Co3O4 (6.4). In addition, the 5 at% Sn-doped Co3O4 exhibits rapid response/recovery time (1 s/17 s), excellent anti-humidity properties, good gas selectivity and repeatability as well as superior long-term stability.

Metal-Organic frameworks-derived 2D spindle-like sn-doped Co3O4 porous nanosheets as efficient materials for TEA detection

YSZ-based mixed potential type NH3 sensor has a good application foreground in on-board SCR (Selective Catalytic Reduction) system due to its good thermal and chemical stability. In this study, we greatly improved the NH3 sensing performance of this type of sensor to meet the detection requirement through the development of high-performance sensing electrode materials. FeVO4 was synthesized through a traditional sol-gel method and used as basis material. In order to improve the electrochemical catalytic activity, different molar ratio of metal oxides (NiO, SnO2, WO3) modified FeVO4 were prepared. The cyclic voltammetry (CV), the linear sweep voltammetry (LSV) and dc polarization (I–V) measurements were carried out to confirm the electrochemical catalytic activity of the sensing electrode materials. Eventually, the sensor attached with 20 mol.% NiO modified FeVO4-SE exhibited the highest response (−83 mV) to 100 ppm NH3 and had a low detection limit of 5 ppm. What is more, the sensor also displayed short response and recovery time, satisfying oxygen resistance and good stability over 20 days at 650 °C, indicating its potential for in-situ ammonia monitoring in industrial and automotive applications.

Mixed potential type NH3 sensor based on YSZ solid electrolyte and metal oxides (NiO, SnO2, WO3) modified FeVO4 sensing electrodes

Mixed potential gadolinia-doped ceria (GDC)-based gas sensors using a double perovskite composite oxide (Sr2NiMoO6) were fabricated to detect ethanol. The influence of the sensing materials sintered at different temperatures on the sensor properties was investigated. The results showed that Sr2NiMoO6 annealed at 1000 °C was the most suitable sensing material for detecting ethanol due to its suitable micromorphology and high electrochemical catalytic activity. The sensor attached with Sr2NiMoO6-1000 °C displayed the highest sensitivity to 1–200 ppm ethanol at 550 °C, the response value ΔV was piecewise linearly with the logarithm of ethanol concentration, and the slopes were −8 and −51.3 mV/decade in the ranges of 1–10 ppm and 10–200 ppm ethanol, respectively. Moreover, the stability and sensing mechanism of the sensor were also investigated.

Ethanol sensor using gadolinia-doped ceria solid electrolyte and double perovskite structure sensing material

High-performance YSZ-based mixed potential NH3 sensor has been developed and utilized with the prospect of excellent applications in in-vehicle SCR (Selective Catalytic Reduction) systems. In order to further lower the detection limit and improve the sensitivity to NH3, we prepared Ag decorated FeVO4 as sensing electrode material through the NaBH4 reduction method in this work. Electrochemical methods such as cyclic voltammetry (CV), linear sweep voltammetry (LSV) and I-t curves are used to explore and compare the electrochemical catalytic activity of electrode materials. 3 mol% Ag decorated FeVO4 was considered as the best sensing electrode material because of its highest electrochemical catalytic activity and reliable stability. Also, the reaction product under the sensor’s working condition was confirmed by the online mass spectrometer. The sensor attached with 3 mol% Ag decorated FeVO4-SE could give a response of − 57 mV to 50 ppm NH3 in 3s and recover to base line in 16s, exhibiting its rapid detection ability at high temperature of 550 °C. Moreover, it displayed good selectivity and a low detection limit of 200 ppb. Additionally, the stability of the sensor under different oxygen concentration and humidity was studied in detail.

Mixed-potential ammonia sensor using Ag decorated FeVO4 sensing electrode for automobile in-situ exhaust environment monitoring

Breath analysis is of great significance for the early diagnosis of diabetic ketoacidosis. Gas sensors with simple structure and low cost have become candidates for breath analysis. The detection range and reliability of the device play an important role in the actual application. In this work, we used Bi1-xSrxFeO3 (x = 0.2, 0.4, 0.6, 0.8) prepared by sol-gel method to fabricate Ce0.8Gd0.2O1.95 (GDC)-based mixed potential type acetone sensors, and obtained satisfactory sensing performance. The amount of Sr substitution in sensing materials could change the content of deﬁcient oxygen inside the material and the electrochemical catalytic activity of the material, thereby improving the sensitivity of the sensor. Mixed potential sensing mechanism and the reason for sensitivity segmentation phenomenon were also explained. In addition, we did clinical tests for the sensor towards the exhalation of diabetic patients and healthy people, which displayed the potential of the sensor used for breath analysis.

Tong Wang

Papers

Mixed potential type NH3 sensor based on YSZ solid electrolyte and metal oxides (NiO, SnO2, WO3) modified FeVO4 sensing electrodes

Ethanol sensor using gadolinia-doped ceria solid electrolyte and double perovskite structure sensing material

Mixed-potential ammonia sensor using Ag decorated FeVO4 sensing electrode for automobile in-situ exhaust environment monitoring

Mixed potential type acetone sensor based on GDC used for breath analysis

Mixed potential type acetone sensor based on Ce0.8Gd0.2O1.95 solid electrolyte and La2MMnO6 (M: Co, Cu) sensing electrode