Gas Sensitivity Research Articles

Gas sensitivity of PECVD β-Ga2O3 films with large active surface

The gas-sensitive properties of Ga2O3 films, first synthesized by plasma-enhanced chemical vapor deposition (PECVD), with respect to gaseous species of environmental and industrial interest were investigated in detail. The addition of some N2 during the PECVD process made it possible to reduce the inherent high resistance of Ga2O3 material and increase its gas sensitivity. The PECVD-Ga2O3 films demonstrated high responses to H2, O2 and NH3 with maximum response temperatures of 600 °C, 700 °C and 350 °C, correspondingly. The responses of Ga2O3 films to 1 vol % of H2, 40 vol % of O2 and 1 vol % of NH3 at these temperatures were 400.73 %, 480.22 % and 335.35 %, correspondingly. The short response and recovery times of 7.6 s and 31.0 s have been achieved under H2 exposure. A plausible mechanism of the sensory effect of the PECVD-Ga2O3 films was suggested. Thus, the PECVD synthesized Ga2O3 films demonstrate a large potential for the development of high-speed performance H2 and O2 sensors working at high temperatures.

Adsorption and gas sensitivity properties of graphene and Rh-decorated graphene towards SF6 decomposed gases: A DFT study

In order to solve the serious threat of SF6 decomposed gases (H2S, SO2, SOF2, SO2F2) to the stable operation of electrical equipment. In this study, the geometric structure, adsorption energy, density of states (DOS), sensitivity based on band structure and recovery time of H2S, SO2, SOF2, SO2F2 on graphene and Rh-modified graphene (Rh-graphene) were investigated computationally by density functional theory (DFT). The geometric structure of Rh-graphene was optimized with an average Rh-C bond length of 1.891 Å. According to the analysis of DOS and band structure, the electrical conductivity has a little effect of the Rh-graphene compared with pristine graphene, but Rh modification can regulate the band gap of graphene. The adsorption energy (Ead) and the sensitivity (S) at work temperature indicate that graphene has ideal adsorption and sensing properties for SO2 and Rh-graphene reflects the excellent applicability as the SO2 and SO2F2 gases sensor with the sensitivity of approximately −99 % and −60 %, respectively. The Graphene/SO2 system owns the minimum recovery time of 2154.3 ps. The recovery time of Rh-graphene/H2S and SOF2 is several orders of magnitude smaller than Rh-graphene/SO2 and SO2F2. The analysis of DOS and band structure was used to explain the sensing mechanism. The study would lay a theoretical foundation for the development of SF6 decomposed gases sensor for electrical equipment insulation.

Carbon gas sensors synthesized using acacia auriculiformis tree branches to detect methanol, ethanol, acetone vapors and ammonia gas

Metal oxides and carbon are the prime candidates of gas sensor devices. For the inaugural instance, carbonaceous particulate matter was meticulously derived from the branches of Acacia auriculiformis tree indigenous to Sri Lanka to detect vapor and gas. It is worth noting that biomass derived carbon had hitherto remain unexplored in the realm of vapor and gas detection. Carbon films were fabricated via the doctor blade method. The resistivity characteristic of these carbon samples exhibited discernible variations upon exposure to methanol, ethanol, acetone vapors, and ammonia gas. Notably, the gas-sensing properties of sample derived from the central core and the outer shell of Acacia auriculiformis tree branches were independently assessed in these vapors and gas at ambient temperature. Various analytical techniques, including X-ray diffraction (XRD), UVvisible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), were judiciously employed to scrutinize the structural attribute, optical band gap, chemical composition and surface morphology of the aforementioned carbon film samples, respectively. XRD analyses unequivocally confirmed the successful formation of carbonaceous films. FTIR spectra conspicuously delineated the presence of oxygen within the carbon films. Importantly, the optical band gap of our carbon films manifested within the range characteristic of organic carbon. Furthermore, the resistance of the carbon films demonstrated a significant reduction upon adsorption of each vapor. It is noteworthy that while gas sensitivities and response times were superior for carbon derived from the central core of the Acacia tree branches, the recovery times were notably expedited for carbon synthesized from the outer shell of these branches. The zenith of gas sensitivity, an impressive 187%, was recorded in response to 1000 ppm of methanol vapor, when employing carbon sourced from the central core of the acacia tree branches.

Long-term, rapid and stable acetone gas sensing performance of porous Rgo/flower-shaped ZnO nanocomposites with a hydrothermal synthesis method

It is prominent and imperative to synthesize gas-sensitive materials using energy-efficient and environmentally friendly methods to enhance their properties. The current paper employs hydrothermal method porous reduced graphene oxide (P-rGO) and zinc oxide (ZnO) with flower-like structure complexes (PGZ) to detect the acetone gas. The gas sensitivity of the PGZ sensor demonstrate a response of 30.38 for 50 ppm acetone, accompanied by a rapid response recovery time of 5 s/7 s at operating temperature of 240 °C. Moreover, the remarkable long-term stability (<15 % fluctuation over 9 cyclic response cycles and 7 weeks of intermittent testing) of the PGZ gas sensor ensures its suitability for practical applications. The P-rGO enlarges the specific surface area of the material, which is conducive to accelerating the electron transfer in the reaction as well as the adsorption and desorption of the target gas, resulting in a rapid response recovery time. The porous structure can also effectively inhibit the agglomeration and growth of ZnO nanoparticles, thus improving long-term stability. Consequently, our study provides a new strategy for the application of 2D materials in gas sensing.

Enhancing the O2 sensitivity of [Ru(bpy)3]2+ dye by incorporating SnO2 and Ni:SnO2

Oxygen (O2)-sensitive probes encapsulated in a polymeric matrix have gas sensitivity improved by adding different metal oxide semiconductors (MOSs) to the composition. In this research, O2-sensitive tris(2,2′-bipyridyl) ruthenium(II) chloride ([Ru(bpy)3]Cl2) was chosen as a fluorophore, and SnO2 and Ni:SnO2 additives were used to enhance the oxygen sensitivity of the dye. While preparing sensing agents as a form of thin film and nanofiber, dye and MOSs powders were immobilized into the polymethylmethacrylate (PMMA) matrix in close proximity to each other. The oxygen-induced intensity measurements, decay time kinetics, and kinetic response were investigated for each of the sensing slides in the concentration range of 0–100% [O2]. Signal decreases in the emission-based intensity values of all MOSs-doped [Ru(bpy)3]2+-based complexes were monitored. Compared with free form, Ni:SnO2-doped [Ru(bpy)3]2+-based nanofiber agents exhibited a 4.03-fold increase in signal change (I0/I) ratio. The nanofiber structure, which allows the sensor slide to have a higher surface/volume ratio, allows O2 gas to penetrate more effectively. This can lead to greater interaction of the gas within the sensor matrix, resulting in more sensitive detection. Higher Stern Volmer (Ksv) values, greater O2 -induced sensing capabilities, more linear spectral measurements over larger concentration ranges, and faster response and recovery times show that MOSs-doped [Ru(bpy)3]2+-based sensing agents make promising candidates as oxygen probes.

Biaxila strain modulated high anisotropic gas-sensing performance of C5N-based two-dimensional devices: A first-principles study

Two-dimensional carbon nitride materials have been widely used in many applications such as device fabrication, gas adsorption and separation due to their abundant element resources, high physicochemical stability and excellent electronic properties. In this paper, density functional theory and non-equilibrium Green's function method are used to study the electronic structure, transport characteristics and gas sensitivity of C5N-based structures. The results show that the electron transport exhibits obvious anisotropy, in which the electron transport in the armchair direction is more conductive than that in the zigzag direction. It is worth noting that the negative differential resistance effect exists in both directions. Furthermore, the transport and sensing characteristics of inorganic molecules (NO, CO, NO2, SO2, and NH3) adsorbed on the C5N monolayer are studied. The results show that CO, SO2 and NH3 exist on the surface of C5N in the form of physical adsorption, while NO and NO2 adhere to the surface of C5N in the form of chemical adsorption. The designed C5N gas sensor exhibits high sensitivity to NO and NO2 molecules, reaching 81 % sensitivity to NO2 at a 0.1 V bias voltage. Finally, the effect of strain on the adsorption properties of gas sensing devices is studied. Studies have shown that the application of -4 % strain in the armchair direction significantly increases the current of NO and NO2, significantly improving the performance of the gas sensor. Whether strain is applied to the device or gas adsorption, C5N materials always maintain significant anisotropy. This study shows that C5N is a highly anisotropic and sensitive two-dimensional material, which has broad application potential in the field of electronic properties and gas sensing.

Development and Application of a Nano-Gas Sensor for Monitoring and Preservation of Ancient Books in the Library

Monitoring the gas composition in library environments is crucial for the preservation of ancient books. In this study, TiO2 NTs/CNTs composites were synthesized via a hydrothermal method and utilized as nano-gas sensors for NO2 detection. The surface morphology and element composition of the samples were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Additionally, the gas sensitivity of the prepared TiO2 nanocomposites was evaluated at different temperatures, both with and without ultraviolet light irradiation. The results demonstrate that the synthesized TiO2 NTs/CNTs samples exhibit a large specific surface area due to their titanium dioxide nanotubes (TiO2 NTs) and carbon nanotubes (CNTs) composition. Moreover, these samples display excellent gas sensitivity under ultraviolet light irradiation at temperatures of 120 °C. Compared to uncomposited and non-ultraviolet light irradiated samples, the sensor response rate is significantly improved, enabling effective monitoring of NO2 gas in library environments conducive to preserving ancient books. Overall, our findings highlight that the developed TiO2 NTs/CNTs nano gas sensor holds great potential for monitoring and safeguarding ancient books.

A novel Cu-doped ZnO confined structure: Precisely preparation, and sensitization mechanism for ppb-level H2S gas detection

It is still highly desired and challengeable to design H2S sensor with high selectivity and sensitivity due to its toxicity and new application in biomarkers like monitoring halitosis. Here, we reported a novel confined structure as highly sensitive and selective H2S gas sensor. The sensing material was prepared with a HKUST-1 templated method by atomic layer deposition (ALD) ZnO decorated on HKUST-1 and calcination. The gas sensor exhibits a high gas sensitivity (Ra/Rg = 2.67 @ 2 ppm) with excellent selectivity to H2S. Furthermore, the obtained sensor shows ppb-level detection ability (Ra/Rg = 1.13 @ 0.1 ppm). Apart from releasing electrons by the oxidization of H2S on oxygen vacancies with adsorbed oxygen species O2− on ZnO surface (Langmuir-Hinshelwood mechanism), the Cu was proved to be the active sites, and would react with surficial S species. The suggestion was confirmed by operando XAS (X-ray adsorption spectrum) measurements combined with DFT calculations (Mars-van Krevelen mechanism). This work provides valuable insights for developing efficient sensing materials and understanding the sensing mechanism.

Mining Metal‐Biomolecular Framework/PANI Composite CO Sensor: Material Synthesis, Gas Sensing Performance and Mechanism

AbstractIn addressing the issue of poor gas sensitivity in semiconductor CO sensor materials used in mining, such as pure PANI. This study utilized an ice‐water bath in combination with an in‐situ polymerization method to synthesize a new composite material consisting of Cu(II)‐racemic glutamate nanofibers and PANI. The morphology, structure, and chemical bonds of the composite material were analyzed using scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS) and spectral analysis. The material's ability to detect CO (100–500 ppm) at room temperature was investigated, revealing a response value of up to 6.8 % for 400 ppm CO detection when the composite material was deposited on a ceramic interdigital electrode. The material exhibited good selectivity and responsiveness to CO detection at room temperature, attributed to the heterojunction formed between Cu(II)‐racemic glutamate nanofibers and PANI, which enhanced carrier migration. Consequently, the Cu(II)‐racemic glutamate nanofiber/PANI composite(Cu(II)‐RGlu/PANI) material shows promise as a high‐performance sensing material for CO detection at room temperature and as a low‐power, integrable sensor material for underground coal mines. This research contributes to the development of a theoretical framework for such applications.

Synergistic combination of 2-D MXene and MoO3 nanoparticles for improved gas sensing at room temperature

Abstract MXene Ti3C2Tx (with 30% HF-etched, named Ti3C2Tx-30) plays a pivotal role in the substantial enhancement of the structural modification of molybdenum trioxide (MoO3). Additionally, as the surface MoO3 molecules come in contact with reducing gas moieties, they actively participate in gas sensing at room temperature. The percentage of Ti3C2Tx-30 in the MoO3 matrix was varied as 10%, 20%, and 40%, denoted as MM-10, MM-20, and MM-40, respectively. Structural analysis confirmed the composition of the basic elements, and evolution of TiO2 at higher percentage of Ti3C2Tx-30. Spectroscopy analysis shows the interactions between Ti3C2Tx-30 and MoO3, showcasing work functions of 6.91 eV, 6.75 eV, and 7.21 eV for MM-10, MM-20, and MM-40, respectively, confirming the MM-20 to be an optimum composition. When the samples were exposed to ammonia gas, MM-20 showed high response (93% for 100 ppm) at room temperature, with the response time ~ 10 s. As compared to bare MoO3 these samples showed ten-fold improvement. The excess electrons on the surface of Ti3C2Tx-30 facilitate the formation of O2- species, which also provides stability to the, otherwise-highly-reactive, MXene surface. These species actively react with ammonia molecules in the presence of adsorbed MoO3, thereby changing the resistance of the system. This can be a significant step towards imparting high gas sensitivity to metal oxides at room temperature via incorporation of optimum percentage of optimised Ti3C2Tx.

An Analytical Method for Timely Predicting of Coal Seam Pressure during Gas Production for Undersaturated Coalbed Methane Reservoirs

Coal seam pressure is an important parameter for production performance evaluation and prediction of coalbed methane (CBM). CBM production from undersaturated CBM reservoirs can be divided into two stages according to critical desorption pressure. At present, few prediction models of coal seam pressure performance consider the comprehensive influence of critical desorption pressure, dissolved gas, matrix shrinkage, and stress sensitivity. For the purpose of accurately predicting coal seam pressure during gas production for an undersaturated coalbed methane reservoir, the material balance principle is used to establish the analytical method for predicting coal seam pressure, considering the comprehensive influence of the critical desorption pressure, dissolved gas, matrix shrinkage, and stress sensitivity. Then, the proposed method is verified against a numerical simulation case using a computer modelling group (CMG) and two actual coalbed methane wells. Finally, the sensitivities of influencing factors on the coal seam pressure are analyzed. The results show that good agreements were obtained between the calculated coal seam pressures using the proposed method and those from the CMG-GEM simulation case and actual CBM wells, with the relative errors all being less than 1%. When ignoring the influence of critical desorption pressure and mistaking pd for pi as well as ignoring Cs, the relative error can reach as high as 31.3%. The main factors affecting the coal seam pressure are the critical desorption pressure and free gas saturation. The proposed method is simple to use, and without shutting-in the well, it can provide an important basis for production performance evaluation and development strategies.

In Situ-Derived N-Doped ZnO from ZIF-8 for Enhanced Ethanol Sensing in ZnO/MEMS Devices.

Microelectromechanical systems (MEMS) gas sensors have numerous advantages such as compact size, low power consumption, ease of integration, etc., while encountering challenges in sensitivity and high resistance because of their low sintering temperature. This work utilizes the in situ growth of Zeolitic Imidazolate Framework-8 (ZIF-8) followed by its conversion to N-doped ZnO. The results obtained from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate that the in situ derivation of ZIF-8 facilitates the adhesion of ZnO particles, forming an island-like structure and significantly reducing the interfaces between these particles. Furthermore, powder X-ray diffraction (XRD) analysis, elemental mapping, and X-ray photoelectron spectroscopy (XPS) analysis confirm the conversion of ZIF-8 to ZnO, the successful incorporation of N atoms into the ZnO lattice, and the creation of more oxygen vacancies. The ZIF-8-derived N-doped ZnO/MEMS sensor (ZIF (3)-ZnO/MEMS) exhibits remarkable gas sensitivity for ethanol detection. At an operating temperature of 290 °C, it delivers a substantial response value of 80 towards 25 ppm ethanol, a 13-fold enhancement compared with pristine ZnO/MEMS sensors. The sensor also exhibits an ultra-low theoretical detection limit of 11.5 ppb to ethanol, showcasing its excellent selectivity. The enhanced performance is attributed to the incorporation of N-doped ZnO, which generates abundant oxygen vacancies on the sensor's surface, leading to enhanced interaction with ethanol molecules. Additionally, a substantial two-order-of-magnitude decrease in the resistance of the gas-sensitive film is observed. Overall, this study provides valuable insights into the design and fabrication strategies applicable to high-performance MEMS gas sensors in a broader range of gas sensing.

Adsorption and gas sensitive behavior of Co2+ doped TiO2(101) crystal planes

Density functional theory (DFT) and Electrochemical Impedance Spectroscopy (EIS) were used to study the molecular adsorption behavior of the Co2+ doped TiO2(101) crystal plane, and the ethanol molecular gas sensitivity test was performed. Theoretical models indicate that doping leads to oxygen defects on the crystal plane and further chemisorption of two oxygen molecules, resulting in reduced electrical conductivity and improved oxygen storage capacity on the crystal plane. Ethanol molecules do not compete with N2, O2, and H2O molecules on doped crystal planes because of their different adsorption active sites, which means that the response time of gas-sensitive detection of ethanol molecules is short and is not interfered with the air molecules in the test environment. These results were confirmed by EIS and gas sensitivity experiments. The change of electrical conductivity after the adsorption of molecules on the crystal plane was confirmed by EIS. The enhanced oxygen storage capacity of the doped crystal plane was confirmed by the expansion of the linear response range of gas-sensitive detection from 20-100 ppm before doping to 20–1200 ppm. This provides a scientific basis for effectively shortening the gas-sensitive response time, increasing the concentration range, improving the oxygen-carrying capacity, and enhancing the catalytic and gas-sensitive properties of the material.

Improved ammonia sensitivity and broadband photodetection by using PBTTT-C14/WS2-QDs nano-heterojunction based thin film transistor

An ambient temperature broadband photo-detector and ammonia (NH3) gas sensor devices are developed with PBTTT-C14/WS2-QDs heterojunction thin film. Gas and photo-sensitive semiconducting composite thin layer of PBTTT-C14 conjugate polymer and hydrothermally synthesized WS2-QDs have been deposited by high yield and cost-effective ‘floating film transfer method’ (FTM), which works as a channel (p-type) of the thin film transistor (TFT). To determine the NH3 sensing behavior of the TFT, different concentrations have been exposed of NH3 (0.5-20 ppm) on the channel of the TFT, which shows the response of ~ 50% at 10 ppm ammonia concentration, which is significantly higher than PBTTT-C14 only TFT. This improvement is made possible by the NH3-responsive depleted layer of polymer/QDs heterojunction, which varies widely in the presence of ammonia. As a consequence, the ON/OFF ratio, carrier mobility and threshold voltage (Vth) of the device changes in a wider range. Besides, this TFT based gas sensor is also highly selective to the other interfering gases. In addition to NH3 gas sensitivity, This TFT also shows very high photosensitivity under white light illumination that enhances ‘ON’ and ‘OFF’ current of the device by ~ 2.2 and 70 times, respectively under one sun white light illumination, whereas Vth of the device is shifted by ~ 22V. Besides, the device shows quite fast response/ recovery time under NH3 gas exposure and light illumination.

In-situ constructing Se/SnO2/SnS2/SnSe2/SnSe nanocomposites for rapid detection and highly-sensitive H2S gas sensor

The bare SnS2 usually exhibits many undesirable gas-sensing performances such as low selectivity, slow response/recovery, and poor stability in the application field of gas sensors. Heterojunction and morphology engineering are crucial for achieving high-performance SnS2-based gas sensors. Here, we firstly fabricated SnS2 nanoflowers, and subsequently on the SnS2 nanoflowers’ microstructure in-situ constructed Se/SnO2/SnS2/SnSe2/SnSe nanocomposites by two-step solvothermal methods. In contrast to the pure SnS2 and SnSe2 samples, the Se/SnSe2/SnS2-based composites display a remarkable improvement in the H2S sensing properties. The phase composition, microstructure, and gas-sensing properties of the composites are well modulated by varying the S/Se ratio. The test results reveal that the S/Se-0.2 (SnS2/SnSe2 ratio = 1:5) sensor exhibits a high gas response of Ra/Rg = 11.07 and a fast response and recovery of 6 s/148 s toward 200 ppm H2S at 200 °C. More importantly, the S/Se-0.2 sensor shows remarkable selectivity, good reproducibility, and excellent long-term stability to H2S with a low detection limit of 250 ppb. The sensing mechanism is also investigated based on XRD, XPS, and SEM analysis. The strengthened gas sensitivity for the S/Se-0.2 sensor is the synergistic effects of the microstructure, defects, and multiple heterojunctions. Our work paves a new road for the design and optimization of SnS2-based gas sensors.

Adsorption Properties of Dissolved Gas Molecules in Transformer Oil on the ReSe2 Monolayer: A DFT Study.

Based on density functional theory, the adsorption behavior of seven typical dissolved gas molecules (CO, CO2, H2, CH4, C2H2, C2H4, and C2H6) and H2O molecule on the ReSe2 monolayer was systematically investigated. The interactions between the ReSe2 monolayer and eight gas molecules were investigated by calculating the adsorption energies, charge transfer, density of states (DOS), and deformation charge density (DCD) for eight different adsorption systems. The gas sensitivity of the ReSe2 monolayer toward these gases was studied using frontier molecular orbital theory and work function analysis. The results demonstrate that compared to other gas molecules, the ReSe2 monolayer exhibits a stronger interaction with CO with an adsorption energy of -1.49 eV. It also displays excellent sensitivity and selectivity toward CO making it a promising candidate for CO gas sensing applications. We aspire that this research will offer theoretical guidance for the development of ReSe2-based gas sensors and contribute to state monitoring technology in oil-immersed power equipment.

Highly sensitive Pt-functionalized In2O3/SnS2 nanoflowers to realize the rapid detection of H2S gas

Recently, SnS2 sensing material has received lots of attention in the application of gas detection owing to its merits of high physical affinity and appropriate bandgap width. Nevertheless, the gas sensors based on SnS2 sensing materials are subjected to the shortcomings of poor selectivity and long response/recovery induced by the low conductivity of SnS2 material. This article employs a secondary solvothermal method to prepare flower-like In2O3/SnS2 heterostructures modified by noble metal Pt nanoparticles to realize the rapid detection of H2S for the first time. The gas-sensing tests indicate that this heterostructure greatly improves the pure SnS2 material’s conductivity and enhances the adsorption capacity for H2S gas molecules. Compared with pure SnS2 and In2O3/SnS2 sensors, the Pt-In2O3/SnS2 sensor presents superior repeatability during multiple measurement cycles and excellent selectivity towards H2S at the optimum operating temperature of 220 ℃. The sensor also exhibits a fast response/recovery of 10 s/506 s together with a large gas response of 11.98 toward 200 ppm H2S. The strengthened sensing characteristics are primarily attributed to the abundant active sites in the Pt-In2O3/SnS2 composites, the excellent carrier transfer ability caused by the In2O3/SnS2 heterojunction, the strong gas adsorption ability induced by noble metal platinum, and the modulated Schottky barrier. Our work provides an effective route for the improvement of the gas sensitivity of SnS2-based H2S gas sensors.

Ar plasma-engraved rGO/In2O3 hollow nanospheres with rich oxygen vacancies for enhanced triethylamine detection

We successfully constructed a high-performance In2O3 based triethylamine sensor using rGO combined with Ar plasma treatment (Ar-rGO/In2O3). The Ar plasma treatment and rGO doping did not cause significant changes to the crystal structure of In2O3 hollow nanospheres, but increased the content of oxygen vacancies in In2O3, while making the structure of In2O3 hollow nanospheres more porous and thin-walled. The gas sensitivity test results show that this new Ar-rGO/In2O3 based sensor has the advantages of high response (Ra/Rg = 172 to 100 ppm, 4.2 times that of pure In2O3 material), low detection limit (0.5 ppm), fast response speed (1 s), and good stability to triethylamine. It also has excellent selectivity, repeatability, and long-term stability. This work is of great significance for understanding the relationship between response and surface oxygen vacancies of sensitive materials, as well as promoting the development of new triethylamine sensors.

A formaldehyde gas sensor based on Ag-decorated ZnCo2O4/FF composite

Cobalt-containing spinel oxides are highly active materials for gas sensing and have shown promise in various applications. In this study, we prepared a series of gas-sensitive composites by doping Ag into ZnCo2O4/Phenylalanine dipeptide (ZCO/FF) and investigated their gas sensitivity to formaldehyde. The experiments showed that the response of ZCO/FF-3 wt%Ag to 20 ppm formaldehyde was 23 at an optimum operating temperature of 175 °C. Further experimental data show that the sensor has excellent selectivity and stability. These results provide basic knowledge for the practical use of spinel oxide gas sensors.

Combustion synthesis of spinel structured NiCo2O4 nanostructures: An efficient material for gas sensing and supercapacitor electrode applications

Nanostructured spinel NiCo2O4 powder has been effectively synthesized using the solution combustion technique. The synthesized material was annealed at 500 °C and further utilised for gas sensing and energy storage applications. The thermal, structural, optical, electrical, magnetic and morphological properties of synthesized material were investigated in detail. The annealed synthesized NiCo2O4 powder was tested for the electrochemical studies with galvanostatic charge-discharge (GCD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and cyclic stabilitytests for the supercapacitor electrode applications. The specific capacitance (CS), energy density (E) and power density (P) of the synthesized materials were estimated from the GCD plot and it was 730 F/g, 16.22 WhKg−1 and 398.71 Wkg-1 respectively at the current densities 2 A/g. The fabricated electrode from NiCo2O4 powder had an initial retention of capacitance value is 92.23 % after 5000 cycles. The synthesized material was further tested with different gases detection at various temperatures. The fabricated NiCo2O4 sensor was used for the estimation of gas sensing properties of acetone, carbon dioxide, ammonia and ethanol gases at various working temperatures. The gas-detection measurements illustrate that the NiCo2O4 material reacts differently to various gases at different temperatures and observes maximum sensitivity, superior selectivity, quick response and recovery ability for the ammonia gas as compared with other test gases. The feasible NH3 gas detection mechanism is pictorially presented in this manuscript. The present works conclude that nanostructured spinel NiCo2O4 is the promising material in the high performance electrode material for supercapacitor applications and ammonia gas sensing application.