Recovery Time Of Sensor Research Articles

The effect of simultaneous Al-doping and Pt-decoration on the sensitivity of a ZnO nanocluster toward acetone

In 2019, Koo et al. have experimentally shown that the sensitivity of ZnO nanostructures is increased toward acetone gas by simultaneous Al-doping and Pt-decoration. Here, we performed a density functional theory study to explore the origin of the experimental observations on the molecular level in terms of orbital, density of states, electronic, energetic, and charge transfers. We defined a relationship between the sensor response (R) and its HOMO-LUMO energy gap, which indicates a good agreement with the experimental results. The acetone interacts weakly with the pristine ZnO with the adsorption energy (Ead) of -15.6 kcal/mol. By Al-doping, the Ead increases to -38.4 kcal/mol and the R value is predicted to be 246. By Pt-decoration, the number of adsorbed acetone and charge transfer are increased, increasing the R value to 447, which is close to the experimental value of 421. The sensor recovery time is predicted to be 383 s, being close to the experimental value of 440 s.

Hydrogen detection on black phosphorene doped with Ni, Pd, and Pt: Periodic density functional calculations

This article reports predicted hydrogen sensing performance data for black phosphorene (BP) monolayer doped with group 10 elements (Ni, Pd, and Pt) at the HSE06/Def2-TZVP level of theory. Different among others, the H2 molecule adopted a parallel configuration over the Ni-BP surface in the armchair direction. The stabilization of hydrogen over the four BP sensors led to small adsorption energies (up to −0.27 kcal/mol). The BP modification led to an indirect bandgap and n-type doping behavior. The reported results confirmed that nickel doping could transform the pristine BP to a sensitive, reusable sensor (recovery time up to 1.6 ps) with reasonably high response of 28.2 at room temperature. In selectivity terms, however, the Ni-BP was found to be an efficient sensor for hydrogen purification. The Ni-BP material was the best work function sensor in this series as well. However, the Pt-BP sensor demonstrated a higher selectivity (4.56) in nitrogen. The results were also discussed in terms of the quantum theory of atoms in molecules (QTAIM), non-covalent interactions (NCI), formation energy, and surface diffusion. These data would be quite relevant to the rational design of novel sensors of hydrogen.

Nanostructured Spin Ladder Compound CaCu2O3 based Gas Sensor for the Detection of Volatile Organic Compounds

Several volatile organic compounds (VOCs) are found in human breath and the concentrations of such VOCs are usually measured to be at sub-ppm level or even lower for healthy human beings. Abnormal concentrations of the breath VOCs are reported to correlate with unhealthy/injurious body/organ conditions; for instance, acetone gas for diabetes, trimethylamine for uremic patients and ammonia gas for renal disease. Hence, VOCs can potentially be used as disease-specific biomarkers for non-invasive early detection or monitoring from breath. Acetone can be produced via the fatty acid oxidation in diabetes and ketoacidosis lack of insulin. Excessive acetone circulating in the blood system is excreted from the lungs. Higher acetone concentration ranges from 1.7 ppm to 3.7 ppm could be detected in breath for those who are diabetic, while the breath of healthy human typically contains less than 0.8 ppm. Gas sensors with sub-ppm acetone detection capacity play an important role in the development of non-invasive monitors or early diagnosis of potential diabetic patients. Up to date, various gas sensors have been successfully developed to detect acetone by controlling the morphology of nanomaterials or introducing the noble metals into nanoparticles. Although, these sensors had achieved the purpose to detect acetone gas, the high operating temperature, higher-energy cost, and the long response time still limit their further applications in practice. Great effort has been made to improve that, by choosing novel material. In order to solve these problems, the present work will focus on the design and development of gas sensors based on new nanomaterials CaCu2O3 offer extremely large surface-to-volume ratio, and the possibility to modify their surface reactivity to attain high sensitivity at low concentration (ppt or lower) required for detection of acetone.CaCu2O3 nanoparticles were synthesized by microwave irradiation method. The structural, morphological, electrical properties were studied by HRSEM, XRD and electrical measurements. The response of CaCu2O3 sensors to acetone at different operating temperatures is reported. It can be noted that the maximum of response to acetone observed at 200°C. The resistance change of the sensor to temperature change is quick and the baseline stabilization is attained in a brief time. The response of the sensor to acetone pulses is reversible and fast (τres ~ 5 seconds). Further, a considerable decrease has been observed in the recovery time (τrec ~ 20 seconds), which is another key advantage of this CaCu2O3.The reproducibility and repeatability are other important factors for a acetone gas sensor. The cycling performance of the fabricated sensor at 200°C shows that the response to 100 ppm of acetone is the same when the measurements were repeated for 10 times consecutively, indicating the excellent reproducibility. Furthermore, the long-term stability of the sensor was also evaluated for many months, and the responses are nearly the same, demonstrating the good stability of the developed sensor.CaCu2O3 nanorods have been prepared by microwave irradiation method and their gas sensing properties towards acetone and ethanol are investigated. All the fabricated sensors show reversible resistance changes while exposed to acetone. The gas sensing measurements of CaCu2O3 sensor exhibited high sensitivity and good selectivity towards acetone. Further, the fabricated sensor showed remarkable increase in sensor response and recovery times. The developed CaCu2O3 sensor is most promising candidate for highly sensitive and selective detection of acetone for medical applications.

A SILAR fabrication of nanostructured ZnO thin films and their characterizations for gas sensing applications: An effect of Ag concentration

Gas sensing device development is a key field of research in the recent scenario, Hence, in this work, facile fabrication of ZnO films with diverse content of Ag was accomplished as a vapor sensor using a cost-effective successive ionic layer adsorption and reaction (SILAR) process. X-ray diffraction (XRD) analysis provides evidence about the good crystalline nature of grown ZnO: Ag films and crystallite size was decreased from 38 to 27 nm with Ag content increased from 0 to 5 wt.%. Scanning electron microscope (SEM) analysis revealed the remarkable modification in morphology from nanograins (undoped) to nanorods (5 wt.% Ag). Energy dispersive analysis of X-rays (EDX) supports the Zn, O, and Ag content present in the final film. The prepared Ag-doped ZnO films exhibited good optical nature and an improvement in the energy gap from 3.04 to 3.29 eV was noticed. The responsivity, response and recovery time of ammonia vapor sensor were remarkably enhanced to 8260 %, 27 s, and 7 s respectively, for the 5 wt.% Ag doped ZnO nanofilm. The responsivity of 5 wt.% Ag doped film was 15 times that of undoped ZnO film. These results make low cost grown Ag-doped ZnO nanorod a good candidate for high quality vapor sensor.

Development of ZnO-based sensors for fuel cell cars equipped with ethanol steam-reformer for on-board hydrogen production

In this paper, pure (ZnO) and doped-zinc oxide (Mo- and Cr-ZnO) samples were prepared, characterized and investigated as sensing material with the main objective to develop a conductometric sensor platform that can detect hydrogen and ethanol, for application in fuel cell cars equipped with ethanol steam-reformer for on-board hydrogen production. ZnO-based nanomaterials were synthesized by a simple wet chemical method and characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. ZnO sample was found to possess a well defined dumbbell-like morphology, while Mo- and Cr-ZnO samples showed non ordered structures at micrometric level. Sensing tests revealed that the sensor response to H2 and ethanol is largely dependent on the temperature, nature and loading of dopant. ZnO-based sensor showed very good performance in terms of sensor response (R0/R = 10–@2000 ppm of hydrogen), response and recovery time (5 and 7 s, respectively) at the operating temperature of 400 °C, which are promising characteristics for developing an hydrogen leak sensor. The ZnO sensor showed also good characteristics for detecting selectively ethanol when operating at lower temperature (250 °C). On the other hand, the detection of both gases can be also accomplished using two sensors, namely ZnO and Mo-ZnO, operating both at the same temperature of 250 °C. On the basis of the results reported, a single conductometric platform based on these sensors, can be proposed for detecting leak hydrogen as well as both ethanol fuel and hydrogen, for monitoring the steam reforming process efficiency in fuel cell cars.

Self-standing MWCNTs based gas sensor for detection of environmental limit of CO2

In this work, we have demonstrated multi walled carbon nanotubes (MWCNTs) based CO2 gas sensor using a reliable and low cost gel-cast method with MWCNT concentration of 0.6, 1.0, 1.5, 2.0 and 3.0 by wt% in alumina Al2O3 sol which acts as a host matrix for the composite. Sensing response of the as prepared highly uniform self-standing MWCNTs film was measured at room temperature by exposure to different CO2 concentrations, ranging from 50 ppm to 450 ppm. The adsorption effect of CO2 on the varying concentration of CNTs was investigated by measuring a significant change in the resistance. Upon exposure to CO2 molecules, the device shows a drastic increase in resistance attributed to the charge transfer between CNTs and CO2 molecules. High sensor response of 7.3% with a response time of 53.7 s exhibited by sensor S3 (1.5 wt% of MWCNTs) is reported when the concentration of CO2 is 450 ppm in ambient conditions. In addition, different recovery modes were examined and the results reveal that there is a significant decrease in the recovery time of sensor upon UV light exposure and heat application. Besides being fast recoverable with heat energy, the fabricated gas sensor shows favorable stability in response over multiple exposure of analyte gas.

Catalytic Filter for Continuous and Selective Ethanol Removal Prior to Gas Sensing.

Ethanol is a major confounder in gas sensing because of its omnipresence in indoor air and breath from disinfectants or alcoholic beverages. In fact, most modern gas sensors (e.g., graphene, carbon nanotubes, or metal oxides) are sensitive to ethanol. This is challenging because ethanol is often present at higher concentrations than target analytes. Here, a simple and modular packed bed filter is presented that selectively and continuously removes ethanol (and other alcohols like 1-butanol, isopropanol, and methanol) over critical acetone, CH4, H2, toluene, and benzene at 30-90% relative humidity. This filter consists of catalytically active ZnO nanoparticles (dBET = 55 nm) made by flame aerosol technology and annealing. Continuous oxidation of ethanol to CO2 and H2 was observed at filter temperatures above 260 °C while below that, unwanted acetaldehyde was formed. Most remarkably, ethanol concentrations up to 185 ppm were removed from exhaled breath in preliminary tests with an alcohol intoxicated volunteer, as confirmed by mass spectrometry. At the same time, almost 4 orders of magnitude lower (e.g., 0.025 ppm) acetone concentrations were preserved. This was superior to previous catalyst filters (e.g., CuO, SnO2, and Fe2O3) with overlapping ethanol and acetone conversions and related to ZnO's surface basicity. The ZnO filter performance was stable (±2.5% conversion variability) for, at least, 21 days. Finally, when combined with a Si-doped WO3 sensor, the filter effectively mitigated ethanol interference when sensing acetone without compromising the sensor's fast response and recovery times. Such catalytic filters can be combined readily with all gas sensors.

Polymer/Graphene oxide nanocomposite thin film for NO2 sensor: An in situ investigation of electronic, morphological, structural, and spectroscopic properties

The higher operating temperature of metal oxide and air instability of organic based NO2 sensor causes extremely urgent for development of a reliable low cost sensor to detect NO2 at room temperature. Therefore, we present a fabrication of large area Polymer/GO nano hybrid thin film for polymer thin film transistors (PTFTs) based NO2 sensors assisted via facile method named ‘spreading-solidifying (SS) method’, grown over air/liquid interface and successive investigation of effect of NO2 on film via several characterizations. The PTFTs sensor has demonstrated swift and high response towards low concentration of NO2 gas with air stability and provided real time non-invasive type NO2 sensor. Herein, we are reporting the nanohybrid PBTTT/GO composite based PTFT sensor with good repeatability and sensor response for low concentration NO2. The thin film grown via SS technique has reported very good adsorption/desorption of target analyte having response/recovery time of 75 s/523 s for 10 ppm concentration of NO2 gas. It has been observed that % change in drain current (sensor response) saturated with increasing concentration of NO2. The transient analysis demonstrates the fast sensor response and recovery time. Furthermore, in order to understand the insight of high performance of sensor, effect of NO2 on nanohybrid film and sensing mechanism, an in situ investigations was conducted via multiple technique viz. spectral, electronic, structural, and morphological characterization. Finally, the performance of sensor and the site of adsorption of NO2 at polymer chains were argued using schematic diagram. This work shows the simple fabrication process for mass production, low cost and room temperature operated gas sensors for monitoring the real-time environment conditions and gives an insight about the sensing mechanism adsorption site of NO2.

Resistive- and capacitive-type humidity and temperature sensors based on a novel caged nickel sulfide for environmental monitoring

In this work for the first time, a new bis(4-benzylpiperazine-1-carbodithioato-k2S,Sʹ)nickel(II) complex (hereafter caged nickel sulfide) has been used to fabricate the capacitive-type and resistive-type sensor. The surface consisted of 2D plates, pores and pore-channels of various shapes and size. These 2D plates and pores played a pivotal role in the sensing mechanism of the sensor. The conduction mechanism is based on Von Grotthuss mechanism. In the relative humidity (RH) range 30–90%, the resistance of the sensor was decreased by two orders of magnitude (from 2.94 × 108 Ω at 30%RH to 2.34 × 106 Ω at 90%RH at operational frequency of 120 Hz). While at applied frequency of 120 Hz, capacitance of the sensor was increased from 15.95 pF to 38.1 pF in the range of 30–90%RH. At higher frequency (10 kHz) the capacitance of the sensor is reduced to 6.285 pF. The maximum hysteresis of 1.54% is noted which is less than the reported in the literature. The response and recovery time of the sensor were 25 and 30 s, respectively, which are either far smaller or greater than the response and recovery time of the various sensors reported in the literature.

Synthesis of sodium cholate mediated rod-like polypyrrole-silver nanocomposite for selective sensing of acetone vapor

Nanostructured conducting polymer provides higher surface area for analyte vapor sensing. This investigation aims to synthesize rod-like polypyrrole (PPY) silver nanocomposite tailored by sodium cholate surfactant as soft template for sensing of acetone vapor. During oxidative polymerization of pyrrole by ferric chloride Ag nanoparticle gets deposited on PPY by simultaneous reduction of silver nitrate. The crystal structure, surface morphology and nature of interfacial interactions between the two components of the prepared PPY-silver nanocomposite (PPY-Ag) are analyzed by standard characterization techniques. The Ag nanoparticles deposition on rod-like PPY increases with increasing silver nitrate concentration up to an optimum level. The PPY-Ag nanocomposites show chemiresistive type dynamic sensing responses toward methanol, ethanol and acetone vapor in a mixture with air. A comparative evaluation of typical vapor sensing parameters (% response, response time, recovery time, reproducibility, and selectivity) of PPY-Ag nanocomposite sensor obtained for different volatile organic compounds with those of the pristine PPY sensor is reported. Interestingly, the rod-like PPY-Ag nanocomposite is found to selectively sense acetone vapor showing better % response than that of the other analytes, viz., methanol, ethanol, propanol, water vapor and formaldehyde. The differences in their responses for the different analytes and the selectivity toward acetone vapor are established by considering the difference in their interactions with the nanocomposite.

Highly Sensitive and Stable NO2 Gas Sensors Based on SWNTs With Exceptional Recovery Time

Room temperature operable and highly sensitive NO2 gas sensors are fabricated based on (i) random and (ii) aligned networks of single-walled carbon nanotubes (SWNTs). The fabricated sensors are very sensitive, stable, and show shorter recovery time in the presence of UV light. Also, the variation of the response and recovery with network density is analyzed. The thin film resistor (TFR) of random network is fabricated by a reliable, cost-effective, and reproducible vacuum filtration method. The aligned network is fabricated using AC di-electrophoresis (DEP) technique. Electrodes spacing is optimized to avoid the chaining effect of aligned and bridged SWNTs between the gold electrode pair to enhance the stability and sensitivity of the sensor. Both the sensors based on random and aligned networks of SWNTs is tested with NO2 at room temperature. It is found that the sensor made of the aligned network shows ~3.5 times more sensitivity as compared to the random networks gas sensor but recovery time increases. It is also observed that sensors fabricated by TFR and aligned network techniques are stable and having less than 0.02 % and 0.15 % change in resistance with baseline, respectively. The TFR gas sensors fabricated using as prepared (AP) and purified and low functionality (P2) SWNTs show higher stability but less sensitive compared to the aligned network. The measured complete recovery time of sensors based on random and aligned SWNTs are 50 sec and 124 sec, respectively, for 0.5 ppm NO2. It is also observed that as the network density decreases response improves but the recovery time increases.

Facile one-step hydrothermal synthesis of SnO2 microspheres with oxygen vacancies for superior ethanol sensor

This work reports a facile one-step hydrothermal method to synthesize the microsphere SnO2 particles without using any organic agent. The experiment results show that the obtained SnO2 microspheres consisting number of nanocrystalline particles of 2–5 nm in size. Oxygen vacancies are also existing on the surface of the SnO2 microspheres. The as-prepared SnO2 microspheres possess mesoporous structure of remarkably high specific surface area (111.27 m2g-1). The gas sensing properties of the as-prepared SnO2 microspheres for ethanol was investigated. The response and recovery time of SnO2 sensor surprisingly reached to 3 s and 24 s respectively under 100 ppm flow of ethanol at an operating working temperature of 230 °C. The response of sensor for 100 ppm of ethanol is enhanced to 24.9 at 230 °C. The excellent ethanol-sensing performance of the fabricated sensor has been attributed to its small grain size, high specific surface area and number of oxygen vacancies of SnO2. These results indicating that the SnO2 microspheres obtained in this work is a promising and excellent ethanol-sensor material.

Optical fiber coated Zinc Oxide (ZnO) nanorods decorated with Palladium (Pd) for hydrogen sensing

A novel hydrogen (H2) sensor was developed using acid-etched optical fiber coated with zinc oxide (ZnO) nanorods. The sensing performance was done by comparing the acid-etched fiber coated with ZnO nanorods with and without decorated Palladium (Pd). The conventional optical single-mode fiber (SMF) with a diameter of 125 μm has been modified as a transducing platform by etching it to 11 μm diameter using hydrofluoric acid (HF) to enhance the evanescent field of the light propagates in the fiber core. The etched fiber was coated with ZnO nanorods via hydrothermal process by using seeding and growth solution method. The sensing layer was characterized through Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) to verify the properties of ZnO. Catalyst Palladium (Pd) was sputtered onto the ZnO nanorods to improve H2 detection. The developed sensor operating temperature was found to be 150 °C that produces 6.36 dBm increase in response towards the 1% concentration of H2 in synthetic air. It was then tested with different concentration of H2. The sensor decorated with Pd has better performance in sensing compared to non-decorated Pd based on the output power versus time. The sensor best response and recovery times is 6 and 5 min respectively, for acid-etched optical fiber coated with ZnO nanorods decorated with Pd for 0.75% of H2 concentrations at 150 °C. The results indicate the optical fiber sensor might improve the performance towards H2 as oppose to the conventional electrical sensor.

Room-temperature high-performance ammonia gas sensor based on hydroxyapatite film

A room-temperature high-performance ammonia (NH3) gas sensor based on hydroxyapatite (HAp) film with three-dimensional network structure was reported in this paper. The gas sensor was fabricated on the indium tin oxide glass (ITO) interdigital electrode via simple electrochemical deposition technique. The HAp film gas sensor shows good sensitivity, high reproducibility and excellent selectivity to NH3 gas under dry and relative humidity (RH) conditions at room temperature. The response and recovery time of the HAp film gas sensor to 1000 ppm NH3 gas are 23 s and 14 s under N2 (dry) condition, and are 4 s and 11 s under air (RH ≈ 30) condition, respectively. The HAp film gas sensor has no considerable deviation in the 1000 ppm NH3 gas for 3 cycles under N2 (dry), and so is air (RH ≈ 30) conditions. The HAp film gas sensor shows excellent selectivity to methanol, acetone and ethanol under N2 (dry) and air (RH ≈ 30) conditions. Above all, two sensing mechanisms of the HAp film gas sensor to NH3 gas have been also researched in this work.

High sensitive and low-concentration sulfur dioxide (SO2) gas sensor application of heterostructure NiO-ZnO nanodisks

This paper reports the synthesis and characterization of NiO-ZnO nanodisks synthesized through a facile hydrothermal method. The morphological characterizations confirmed the formation of well-defined nanodisks in high density with an average thickness of 60 ± 5 nm. The x-ray diffraction analysis confirmed the well incorporation of the NiO into the matrix of ZnO crystal and the average crystallite size for the NiO-ZnO nanodisks was found to be 39.71 nm. The compositional analysis revealed the formation of pure NiO-ZnO nanostructures. The synthesized NiO-ZnO nanodisks were used as electrode materials to fabricate Sulfur dioxide (SO2) gas sensors and the gas sensor response and recovery times were systematically analyzed with respect to the operating temperatures and the SO2 gas concentration. The observed sensor gas response, response time and recovery time of the fabricated NiO-ZnO nanodisks based gas sensor were 16.25, 52 s and 41 s, respectively, towards 20 ppm SO2 gas at an optimized temperature of 240 °C. Thus, it is believed that the NiO-ZnO nanodisks could be a promising candidate for the fabrication of efficient gas sensors towards toxic and hazardous gases.

Hollow In2O3 microcubes for sensitive and selective detection of NO2 gas

Herein, we report a facile approach for the synthesis of hollow Indium oxide (In2O3) microcubes (HIMC) by two step process which consist of hydrothermal method and followed by air annealing. Kirkendall effect has been employed to transform Indium hydroxide In(OH)3 microcubes (IHMC) to HIMCs. Particularly, the formation of HIMC was studied as function of annealing time. The evolution of hollowness was discussed through Kirkendall effect. Fabricated HIMC films were used to detect NO2 gas up to 100 ppm of concentration. We found that synthesized HIMC had a huge sensing response (S = 1401) towards 100 ppm NO2 gas, which demonstrates the effect of HIMC over simple microcubes. Response (Rs = 16s) and recovery (Rc = 165s) time of sensor were very short, which enables sensor to work rapidly. Also, HIMC sensor found selective for NO2 gas rather ammonia, acetone and carbon dioxide gases. NO2 sensing mechanism for the case of HIMC based sensor was described as per well known oxide based chemiresistive theory. From observations, it is found that the fabricated (HIMC)3hr based sensor is highly selective and sensitive towards NO2 gas at ppm level of concentration and could be undertaken for gas sensing application at various fields.

Experimental Analysis of the Influence of Olfactory Property on Chemical Plume Tracing Performance

In this letter, we investigated the relationship between the performance of chemical plume tracing (CPT) and odor sensing property. Tracking of chemical plumes plays an important role because it facilitates the identification of an odor source. Conventional research has focused on the development of CPT algorithms, whereas the influence of the performance odor sensors on CPT performance has not been investigated. Therefore, in this letter, we first compared the olfactory characteristics of an insect (silkworm moth, Bombyx mori ), which has high CPT performance and the characteristics of an artificial odor sensor. In particular, we focused on and compared the recovery times of the two types of sensors, which plays an important role in the acquisition of odor information. As a result, it was determined that the recovery time for the insect olfactory sensor was ten times faster than that of the artificial odor sensor. We also experimentally evaluated the effect of this difference in the recovery time on CPT performance. CPT experiments using silkworm moths and a robot revealed that there was a correlation between the CPT performance and sensor recovery time. As such, it was demonstrated that it is necessary to improve not only the algorithm but also the sensor recovery time to improve the CPT performance.

Bio-compatible organic humidity sensor based on natural inner egg shell membrane with multilayer crosslinked fiber structure

In this paper, we propose a novel bio-compatible organic humidity sensor based on natural inner egg shell membrane (IESM) with multilayer cross linked fiber structure that can be used as a substrate as well as a sensing active layer. To fabricate the proposed sensors, two different size inter digital electrodes (IDEs) with 10 mm × 4 mm for sensor 1 and 12 mm × 6 mm for sensor 2 are printed on the surface of the IESM through Fujifilm Dimatix DMP 3000 inkjet material printing setup, which have finger width of 100 μm and space of 100 μm. The fabricated sensors stably operates in a relative humidity (RH) range between 0% RH to 90% RH, and its output impedance and capacitance response are recorded at 1 kHz and 10 kHz. The response time (Tres) and recovery time (Trec) of sensor 1 are detected as ~1.99 sec and ~8.76 sec, respectively and the Tres and Trec of sensor 2 are recorded as ~2.32 sec and ~9.21 sec, respectively. As the IESM for the humidity sensor, the natural materials can be implemented in our daily life as they open a new gate way for bio-compatible devices.

Hydrogen sensors: palladium-based electrode

Hydrogen sensors are transducer devices and able to convert the hydrogen concentration in the environment to an electrical signal. The detection and monitoring of hydrogen gas under the explosive limit is the essential issue for its applications as the chemical reactant and energy resource. In this study, the sensing mechanism and principle of the palladium-based hydrogen gas sensors are firstly reported. Then, the physical sensing parameter, measuring range, response time and recovery time of the different hydrogen gas sensors are also reviewed. Moreover, the high response speed hydrogen sensors are introduced for practical usages.

Gas adsorption on the pristine monolayer GeP3: A first-principles calculation

Monolayer GeP3 has promising applications due to a small indirect band gap and high carrier mobility (Nano Lett, 2017, 17, 1833–1838). By employing the first-principles calculation, we investigate the adsorption behavior of five representative gas molecules (CH4, N2, H2, CO, and H2S) on the surface of monolayer GeP3. Our calculations indicate that GeP3 monolayer can directly adsorb these gas molecules. Also, there are impressive adsorption energies and notable charge transfers between GeP3 monolayer and gas molecules. After adsorbing these gas molecules, the electronic property of GeP3 monolayer can be changed dramatically. In addition, the calculated recovery time of monolayer GeP3-based sensor at 300 K is also suitable for CH4, N2 and H2. These results suggest that monolayer GeP3 might have a potential application in molecule sensor for CH4, N2 and H2.