Graphene-CeO2 based flexible gas sensor: Monitoring of low ppm CO gas with high selectivity at room temperature

The metal-oxide semiconductor-based gas sensor has enthralled many researchers worldwide over past few decades. These sensors offer many advantages such as good selectivity, high sensitivity, and reliable and rapid detection of numerous pollutants. Among the pollutants, CO gas is highly toxic, and CO gas concentration of 9 ppm causes harmful effect on human health; thus, high sensitivity of CO gas detection is extremely significant. Herein, we present the room temperature detection of low concentration CO gas by utilizing cerium oxide microflowers anchored on graphene nanoplatelets (GNPs). The GNPs-CeO2 nanocomposite was synthesized using solvothermal method and followed by structural and morphological characterizations were performed using various analytical techniques. The chemiresistive gas sensor was fabricated with a nanocomposite solution drop-casted on cellulose paper as a substrate and silver paste as an electrode. The as-fabricated gas sensor explored for its applicability on CO gas detection with various concentrations and displayed good selectivity over NO2, SO2, NH3, and CO2. The gas sensing response of the device is due to large number of oxygen vacancies in the nanocomposite and the heterojunction between CeO2 and GNPs. The sensor offers a potential platform for metal oxide-based gas sensors operated at room-temperature and displayed good repeatability and stability

CdS based chemiresistor with Schottky contact: Toxic gases detection with enhanced sensitivity and selectivity at room temperature

Surmounting the selectivity issue of gas sensors and detecting low ppm concentration of gases is highly significant for widespread deployments of sensors to build networks in applications including vehicular emission, fuel-based household appliances, and industrial emissions. Herein, a strategy is proposed to improve the selectivity and sensitivity of the cadmium sulfide (CdS) based sensor via changes in contact material by utilizing different metals. CdS was deposited via the SILAR method on three different glass substrates which have Au, ITO, and Ag contacts, respectively, through which Schottky barrier height (SBH) was adjusted between CdS and metal contact. CdS was thoroughly verified by structural and morphological characterization techniques. As-fabricated devices were tested, and gas sensing results suggest that Au and ITO contacts have significantly superior selectivity towards NO2 and CO gases over other gases. Further, experimental values reveal that sensors can detect up to 0.3 ppm and 1.25 ppm, respectively. Good selectivity can be attributed to the regulation of the SBH. Additionally, as-fabricated devices displayed good long-term stability and short response and recovery times. The present study may provide a rational design for fabricating a high-performance chemiresistive gas sensor for the detection of sub-ppm levels of hazardous gases present in the environment. © 2022 Elsevier B.V

Single-Phase High-Entropy Oxide Nanoparticles for Wide Dynamic Range Detection of CO2

Monitoring wide-range carbon dioxide (CO2) levels with superior sensing performance is extremely important for environmental, human health, safety, and space applications. The reported chemiresistive sensors in the literature have critical drawbacks such as high-temperature operation and long response and recovery times (∼25 min), which remains a challenge for developing CO2sensors. Against these drawbacks, we report Gd0.2La0.2Y0.2Hf0.2Zr0.2O2(Y-HEC)-based sensors obtained by depositing Y-HEC on a glass substrate with different electrodes such as gold (Au), indium tin oxide (ITO), and silver (Ag) for CO2gas detection. The as-fabricated Y-HEC sensor with an ITO electrode displayed a maximum sensing response (46.7%) to 10000 ppm CO2gas at room temperature over other electrodes, which is attributed to the optimized Schottky barrier height between the ITO and Y-HEC. Furthermore, the experimental findings of the sensor with an ITO electrode revealed superior sensing characteristics such as wide-range CO2gas detection (250-10000 ppm), faster response and recovery times (49-200 s), high repeatability, strong selectivity to CO2over other gases, good long-term stability, and room temperature operation. Improvements in the CO2-sensing performance are attributed to nonagglomerated nanoparticles leading to the porous structure and high surface area, and intrinsic oxygen vacancies. We present an easy strategy to synthesize sensing materials and improve the desirable sensing performance for the development of practical applications of CO2sensors. © 2022 American Chemical Society. All rights reserved

Single-phase high-entropy oxide-based chemiresistor: Toward selective and sensitive detection of methane gas for real-time applications

Detecting methane (CH4) with good selectivity is one of the most important safety precautions to prevent catastrophic incidents in the current industrial environment. Detection of small molecular size, inert and nonpolar characteristic gases at trace levels using chemiresistive technique at room temperature is still challenging because of weak adsorption between gas and sensing material. Therefore, we fabricated a single-phase high entropy oxide based chemiresistor and tested it towards the various gases and several hydrocarbons at room temperature, but the sensor displayed a higher selectivity to CH4 gas than other gases. Further, the sensor characteristics revealed a significant response to CH4 gas, good response and recovery time, good long-term stability, and an experimental detection limit of 25 ppm. Besides, the as-fabricated sensor is low-cost, small in size and consumes 50 nW power, much lower than the other commercialized light-based sensors. As proof of concept, the fabricated sensor was utilized to measure CH4 gas in a real-time atmosphere. The sensor reflected response characteristics similar to the controlled environment and recovered without carrier gas. This facile approach sheds light on the rational design of high-entropy oxides, paving the way for mass production and commercialization of ultra-trace gas detection sensors with superior sensing capability. © 2022 Elsevier B.V

Humidity-Independent Methane Gas Detection in Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2-based Sensor Using Polynomial Regression Analysis

Chemiresistive gas sensors (CGS) are continuously being developed over other methods for detecting gas/vapor concentrations because of their simplicity of fabrication, compatibility with conventional DC circuits and high accuracy measurement convenience. However, humidity strongly influences sensing response, while the trade-off between humidity independence and gas response is one of the major barriers to limiting CGS for practical applications. In this regard, highly selective methane (CH4) gas sensor is fabricated using Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 (Ce-HEC) as a sensing material and the relative humidity (RH) effect on sensing response has been investigated. Indeed, the RH effect on the sensor response is high and can be seen in all gas concentrations at various RH levels. Therefore, humidity compensation model (HCM) is developed by fitting multivariate polynomial regression techniques to reduce the anti-interference humidity effect. HCM estimates the gas concentrations with a mean absolute percentage error of 5.81%, and a mean absolute error is 3.43 ppm. This study offers a simple and novel strategy for humidity-independent detection of gas/vapors in CGS and estimates gas concentrations with minimum error. IEE