CO Gas Sensor Research Articles

Improved Sensing Properties of CO2 Gas Sensor Based on Li3PO4-Li2SiO3 Thin Film Compared with Li3PO4

A potentiometric CO2 gas sensor was fabricated using the compound Li3PO4-Li2SiO3 thin film as electrolyte, and its sensing performances were compared with the conventional Li3PO4-based sensor. The Li3PO4-Li2SiO3 electrolyte was prepared by RF magnetron sputtering while the Li3PO4 electrolyte by thermal evaporation. The microstructures and phase composition of both sensors were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The sensors were examined in CO2 atmosphere at a large temperature range from 350°C to 500°C. As the testing results revealed, both sensors’ electromotive force (emf) have a good linear relationship with logarithmic gas concentrations, and the Li3PO4-Li2SiO3-based sensor showed higher sensitivity, shorter response and recovery times, and more stable output emf. The novel sensor exhibited sensitivity as high as 90.80 mV/dec, response and recovery times as short as 6.5 s and 17 s at 500°C. After comparison, it is quite clear that the characteristics of the electrolyte have great influence on the sensor's properties. The improvement is considered to be caused by the electrochemical properties of the Li3PO4-Li2SiO3 thin film, whose micro morphologies and higher ionic conductivity help to enhance lithium-ion transmission in the chemical reactions.

Controlled synthesis of Pt and Co3O4 dual-functionalized In2O3 nanoassemblies for room temperature detection of carbon monoxide

Innovative Pt and Co3O4 nanostructure co-decorated In2O3 nanobundles have been successfully developed and demonstrated as high-performance room-temperature CO gas sensors.

Optical CO2 Gas Sensing Based on TiO2 Thin Films of Diverse Thickness Decorated with Silver Nanoparticles

The fabrication, characterization, and CO2 gas detection performance of single component‐based and hetero‐nanostructure‐based optical gas sensors are reported in the present work. Single component‐based structures include (i) TiO2 thin films with varied film thickness (37.45 nm, 51.92 nm, and 99.55 nm) fabricated via the RF sputtering system for different deposition times and (ii) silver nanoparticles (AgNPs) deposited on the glass substrate by the wet chemical method. Hetero‐nanostructures were achieved by decorating the AgNPs on the predeposited TiO2 thin films. The structural, morphological, and optical characteristics of prepared samples were studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and ellipsometry, respectively. XRD analysis of AgNPs confirmed the crystalline nature of prepared particles with average crystallite size of 21 nm, however, in the case of TiO2 films XRD results suggested amorphous structure of all as‐deposited films. size 21 nm. The SEM micrographs confirmed the deposition of AgNPs on the TiO2 thin films. With increasing sputtering time, TiO2 films were found to be denser and more compact, indicating a reduced porosity and higher film thickness. CO2 gas‐sensing properties were investigated by measuring the optical transmission spectra in alone air and in CO2 gaseous atmosphere at room temperature. It was observed that neither TiO2 thin films even with higher thickness nor alone AgNPs could demonstrate any substantial gas‐sensing activity. Nevertheless, TiO2/AgNP hetero‐nanostructured substrates exhibited excellent CO2 gas‐sensing performance as indicated by a huge change in the transmission spectra. The enhanced sensing efficiency of TiO2/AgNP nanostructures owing to synergistic effects suggests a promising role of our manufactured sensors in practical applications.

A first-principles study of gas molecule adsorption on borophene

Borophene, a new two-dimensional material, was recently synthesized. The unique anisotropic structure and excellent properties of borophene have attracted considerable research interest. This paper presents a first-principles study of the adsorption of gas molecules (CO, CO2, NH3, NO, NO2 and CH4) on borophene. The adsorption configurations, adsorption energies and electronic properties of the gas molecules absorpted on borophene are determined, and the mechanisms of the interactions between the gas molecules and borophene are evaluated. We find that CO, CO2, NH3, NO and NO2 are chemisorbed on borophene, while CH4 is physisorbed on borophene. Furthermore, our calculation also indicate that CO and CO2 are chemisorbed on borophene with moderate adsorption energy and NO, NO2 and NH3 are chemisorbed on borophene via strong covalent bonds. Moreover, CO is found as an electron donor, while CO2 an electron acceptor. The chemisorption of CO and CO2 on borophene increases the electrical conductivity, so It seems that borophene has the potential to be used in high-sensitivity CO and CO2 gas sensors.

Development of an Indoor Photovoltaic Energy Harvesting Module for Autonomous Sensors in Building Air Quality Applications

A 50 mm ${\times } \,\, 20$ mm ${\times } \,\, 15$ mm indoor photovoltaic (PV) energy harvesting power module (IPEHPM) has been developed for powering an Internet of Things (IoT) sensor node containing a low-power CO2 sensor for automatic building ventilation. It is composed of a high efficiency PV energy harvesting module and a supercapacitor to produce 3.6–4.2 V output voltage with 100 mA pulse current for up to 600 ms. Storage efficiency analysis and storage efficiency tests of the IPEHPM have demonstrated that with the adopted simple power management scheme, which exempts the commonly used power management blocks of the voltage regulator and the maximum power point tracking to save power, 88.7% average storage efficiency has been achieved at 200 lux. With the newly established PV powering model, the power consumption requirements of an IoT node can be directly converted into the illumination requirements of the PV energy harvester, making the IPEHPM easy to use. IPEHPM powered IoT experiments with a low-power CO2 gas sensor have demonstrated that the IPEHPM is suitable for IoT-based building ventilation applications, where the CO2 concentration level is measured every 150 s at the indoor lighting condition down to 200 lux.

A first-principles study of gas adsorption on monolayer AlN sheet

The monolayer AlN is one of graphene-like 2D material. On the basis of density functional theory (DFT) calculations, the adsorption of CO2, CO, H2, N2, CH4, O2 and NO on the monolayer AlN was investigated. Due to the dipole moment of the Al-N bond, the gas molecules can be adsorbed directly on the AlN sheet. This avoids the problem about formation of metal clusters using metal decorated carbon nanostructures as gas storage materials. Among all the gas molecules, only CO2 on the AlN sheet has strong interaction with adsorption energy of 0.91 eV. While other gas molecules bind to the AlN sheet much weakly with the adsorption energy being less than 0.5 eV. Due to the charge transfer between gas molecules and the AlN sheet, the AlN sheet can be used to gas sensors for CO2, CO, H2, O2 and NO. Moreover, the AlN sheet can be taken potential applications as sorbent materials for CO2 separation and capture from gas mixture.

Utilization of ZnO nanorods growth on a tip of plastic optical fiber toward the realization of low-cost CO and CO2 gas sensor

This study experimentally demonstrates the feasibility of utilizing zinc oxide nanorods for CO and CO2 gas detection via optical scattering. ZnO nanorods are grown on a plastic optical fiber to measure the effect of gas flow on the optical scattering at room temperature. The presence of nanorods minimizes the coupling of the Fresnel reflection. Placing the optical setup in a home-built gas chamber, an obvious distinguished change of the total reflection was observed when different gas concentrations were present. Reduction of reflection due to the presence of gas indicated that forward scattering leak has a dominant effect on the process. In addition, the results demonstrated that detection of CO gas at a concentration as low as 200 ppm had a higher response in comparison with CO2 gas.

Organometallic Synthesis of CuO Nanoparticles: Application in Low-Temperature CO Detection.

A metal-organic approach has been employed for the preparation of anisotropic CuO nanoparticles. These nanostructures have been characterized by transmission and high resolution transmission electron microscopy, field-emission scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The CuO nanoparticles have been deposited as gas-sensitive layers on miniaturized silicon devices. At an operating temperature of 210 °C, the sensors present an optimum response toward carbon monoxide correlated with a fast response (Rn) and short recovery time. A high sensitivity to CO (Rn≈150 %, 100 ppm CO, RH 50 %) is achieved. These CuO nanoparticles serve as a very promising sensing layer for the fabrication of selective CO gas sensors working at a low temperature.

Reducing N2O induced cross-talk in a NDIR CO2 gas sensor for breath analysis using multilayer thin film optical interference coatings

Carbon dioxide (CO2) gas sensing is an important aspect in the biomedical field of capnography, where cheap, fast and accurate measurement of exhaled CO2 vs. time is crucial in the evaluation of lung and tracheal function during surgical anaesthesia and is an under-used bio-marker for underlying respiratory conditions. Current detection methods do not adequately meet these requirements and suffer from considerable cross-talk associated with the commonly used anaesthetic gas nitrous oxide (N2O). In this work, we report how cross-talk can be reduced in a commercially available, low power (35mW) non-dispersive infrared (NDIR) CO2 gas sensor using thin film multilayer optical filters. Current sensor spectral response, spans 2500nm–5000nm via use of a pentanary alloy LED/photodiode optopair grown by molecular beam epitaxy (MBE), resulting in sensor sensitivity to gases with absorption bands in this region, including N2O. To reduce the effective spectral response of the sensor, capturing only CO2, a multilayer thin film optical interference bandpass filter has been designed and deposited directly onto the diode epi-structures using microwave plasma assisted DC magnetron sputtering. Three different coating configurations have been explored; LED-only coated, photodiode only coated and both coated. Gas sensor response to N2O for each coating configuration has been explored. It was found that application of an optical bandpass filter onto both the sensor LED and photodiode only was the most effective method of reducing sensor response to N2O, however no signal was observed in one of the two “LED and PD coated”, therefore optimal coating configuration for cross-talk reduction is subject to further investigation.

A Robust Electrochemical CO2 Sensor Utilizing Room Temperature Ionic Liquids

Next generation CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensors require an enhancement of sensitivity and invariance with regards to CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> detection and environmental factors. For this study, we report and discuss the effective application of room temperature ionic liquids (RTILs) toward the development of a stable electrochemical CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor that provides increased valuation toward commercial applications. We have investigated two RTILs on both gold and carbon paste electrodes on printed circuit boards over four different CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentrations. We also have investigated another RTIL on a gold electrode for initial repeatability effects at two CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentrations. Using electrochemical impedance spectroscopy and chronoamperometry, we compare and contrast the initial response behaviors for these RTILs for these sensors. This analysis has aided in the identification of robust combinations of RTIL/electrode toward environmental CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors.

The effects of excess carbon on the surface area and crystallinity of TiO2 powders prepared by oxidizing mechanically-synthesized TiC and their CO gas-sensing properties

Abstract TiC-ec (with 20 at% excess carbon), with TiC and TiN powders as comparative samples, were synthesized via ball milling. TiO 2 -ec and TiO 2 -n, TiO 2 -c sensing materials were prepared by oxidizing the synthesized TiC-ec, TiC, and TiN powders at 600 °C. Structural characterization was performed via X-ray diffraction, field emission scattering electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The mean particle size of TiO 2 -ec was the smallest (40.8 nm), and its SSA was the largest (14.3 m 2 /g). The anatase crystallinity of the TiO 2 -ec powder was higher than those of the TiO 2 -n and TiO 2 -c samples, although the particle size was the smallest. The response of TiO 2 -ec to 1000 ppm CO gas at a working temperature of 550 °C was the highest (4.0) while the TiO 2 -c and TiO 2 -n samples showed a smaller response (1.2 and 1.4, respectively). The improved sensing properties of the TiO 2 -ec samples were due to a better crystallinity and larger surface area. Therefore, the enhanced surface area and crystallinity of the TiO 2 -ec are believed to be related to the presence of excess carbon.

Facile synthesis of La2O2CO3 nanoparticle films and Its CO2 sensing properties and mechanisms

In this paper, we presented a simple method to fabricate size-controlled La2O2CO3 nanoparticle by annealing La(OH)3 nanocrystallines in air atmosphere. The microstructures of the samples were analyzed by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and scanning electron microscope (SEM). TEM images indicate that the La(OH)3 precursors consists of uniform ellipsoids with width of 9–15nm and length of 15–30nm and La2O2CO3 are spheroidal particles with size of 12–25nm. XRD patterns indicate that La(OH)3 nanocrystallines are hexagonal phase and transform to monoclinic La2O2CO3 after annealing. And then, La2O2CO3 nanoparticle is printed on an interdigital electrode as a sensing material for CO2 detection. La2O2CO3 sensor exhibits good cycle stability performance and fast response and recovery (53s and 120s) over the wide range of 300–5000ppm CO2 in air condition. In addition, we also investigate the effect of oxygen concentration in the background atmosphere on CO2 response of La2O2CO3 sensor. The CO2 sensing mechanisms for La2O2CO3 sensor can be attributed to the interaction of CO2 with oxygen species on La2O2CO3 surface including chemisorption, surface reaction and desorption process, which also can be used to explain other metal oxide based CO2 gas sensor.

Electric field improved the sensitivity of CO on substitutionally doped antimonene

The geometrics and electronic structures of substitutionally doped antimonene and the interaction between CO molecule different substrates have been investigated using first-principles calculations to exploit the sensitivity of CO to antimonene. It is found that CO adsorption on pristine antimonene is physical adsorption, while it is converted to chemical adsorption after doping. The results indicate that an external electric field (V) ranges from −0.5eV/Å to 0.21eV/Å could improve the CO gas sensitivity of the antimonene, which is helpful to realize the use of CO gas sensor at room temperature. The adsorption and desorption of CO molecule could be controlled by external electric field too, which is helpful to collect and storage of CO gas.

Lightweight, Room-Temperature CO2 Gas Sensor Based on Rare-Earth Metal-Free Composites-An Impedance Study.

We report a light, flexible, and low-power poly(ionic liquid)/alumina composite CO2 sensor. We monitor the direct-current resistance changes as a function of CO2 concentration and relative humidity and demonstrate fast and reversible sensing kinetics. Moreover, on the basis of the alternating-current impedance measurements we propose a sensing mechanism related to proton conduction and gas diffusion. The findings presented herein will promote the development of organic/inorganic composite CO2 gas sensors. In the future, such sensors will be useful for numerous practical applications ranging from indoor air quality control to the monitoring of manufacturing processes.

Room temperature CO2 gas sensors of AuNPs/mesoPSi hybrid structures

Mesoporous silicon (mesoPSi) layer prepared by a laser-assisted etching process in HF acid has been employed as CO2 gas sensors. The surface morphology of mesoPSi was modified by embedding gold nanoparticles AuNPs by simple and quick dipping process in different gold salts concentrations to form mesoPSi/AuNPs hybrid structures. Morphology of hybrid structures was investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrical characteristics of the prepared gas sensor were carried out at room temperature. It was found that the nanoparticles size, shape and the specific surface area of the nanoparticle strongly influence the current–voltage characteristics. Considerable improvement was noticed in sensitivity, response and recovery times of gas sensor with decreasing incorporated AuNPs into the mesoPSi matrix.

Amperometric CO2 gas sensor based on interconnected web-like nanoparticles of La2O3 synthesized by ultrasonic spray pyrolysis

Thin films of La2O3 were deposited onto glass substrates by ultrasonic spray pyrolysis. Their structural and morphological properties were characterized by X-ray diffraction, Fourier transform Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photo-electron spectroscopy, Brunauer-Emmett-Teller and optical absorption techniques. The sensor displays superior CO2 gas sensing performance at a low operating temperature of 498 K. The signal change on exposure to 300 ppm of CO2 is about 75%, and the signal only drops to 91% after 30 days of operation.

Enhanced sensitivity and selectivity of CO2 gas sensor based on modified La2O3 nanorods

La2O3 thin films are synthesized successfully by simple microwave assisted chemical method and characterized with structural and morphological characterisation techniques. CO2 gas sensing properties of La2O3 thin films are enhanced significantly by palladium (Pd) sensitization. La2O3 thin film shows maximum sensitivity of 25% at temperature of 723 K and concentration of 400 ppm CO2 gas, which enhanced to 64% at temperature of 523 K after Pd sensitization.

CO2 gas sensors based on Yb1−xCaxFeO3 nanocrystalline powders

In this study, the Yb1–xCaxFeO3 (0≤x≤0.3) nanocrystalline powders were prepared by sol-gel method. We used the method of quantitative analysis to research the gas-sensitive properties for Yb1–xCaxFeO3 to CO2. Also, we investigated the effects of various factors on gas sensing properties by simple variable method. The doping of Ca could not only decrease the resistance of YbFeO3, but also enhance its sensitivity to CO2. When the Ca content x=0.2, Yb1–xCaxFeO3 showed the best response to CO2. The response Rg/Ra to 5000 ppm CO2 for Yb0.8Ca0.2FeO3 at its optimal temperature of 260 °C with the room temperature humidity of 28%RH was 1.85. The response and recovery time decreased with an increase of the operating temperature for Yb0.8Ca0.2FeO3 sensor to 5000 ppm CO2. Furthermore, with an increase of CO2 concentration from 1000 to 50000 ppm, the response time of Yb0.8Ca0.2FeO3 became shorter, and meanwhile the recovery time was longer. CO2-sensing response for Yb0.8Ca0.2FeO3 increased with the increase of relative humidity. The response for Yb0.8Ca0.2FeO3 in the background of air (with the room temperature humidity of 39%RH) at 260 °C could reach 2.012 to 5000 ppm CO2, which was larger than the corresponding value (1.16) in dry air.

비분산 적외선 이산화탄소 가스센서 특성의 온·습도 영향

비분산 적외선 이산화탄소 가스센서 특성의 온·습도 영향

Carbon monoxide gas sensing at room temperature using copper oxide-decorated graphene hybrid nanocomposite prepared by layer-by-layer self-assembly

A sub-ppm-level CO gas sensor based on copper oxide (CuO)-decorated graphene hybrid nanocomposite was reported in this paper. The CuO/graphene hierarchical nanocomposite was successfully deposited on a substrate with interdigital microelectrodes via layer-by-layer self-assembly technique. The morphologies, microstructures and compositions of the as-prepared CuO/rGO film were sufficiently characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The gas sensing properties of the CuO/graphene nanocomposite was investigated at room temperature over a wide range concentration of CO gas from 0.25ppm to 1000ppm. The experimental results exhibited not only an unprecedented detection abilities, but also fast response and recovery times, excellent repeatability, good stability and selectivity. The superior sensing mechanism for the presented sensor was ascribed to the hierarchical porous nanostructure and the formed heterojunction at the interfaces between CuO nanoflowers and rGO nanosheets.