CO Gas Sensor Research Articles

A catalytic combustion-type CO gas sensor incorporating aluminum nitride as an intermediate heat transfer layer for accelerated response time

Abstract. A catalytic combustion-type carbon monoxide gas sensor exhibiting good sensing performance even at moderate temperatures was previously developed by employing a Pt loaded CeO2–ZrO2–SnO2 solid solution as the CO oxidizing catalyst. The addition of aluminum nitride as an intermediate heat transfer layer between the Pt coil and the CO oxidizing catalyst drastically accelerated the response of this device to CO at temperatures as low as 70 °C.

Novel CO2 and CO gas sensor based on nanostructured Sm2O3 hollow microspheres

Sm2O3 microspheres were prepared by the coprecipitation method, using samarium nitrate and formic acid. The size of the microspheres was in the range 1–6μm; however, extensive fragmentation was observed. An outstanding improvement of the microstructure was achieved by using an aqueous solution of pectin. In this case, hollow and nanoporous microspheres, having little fragmentation, were produced. The evolution of the crystal structure with calcination temperature revealed the formation of single-phase cubic Sm2O3, at 600°C. The effects of the calcination temperature and the concentration of samarium nitrate, on the microstructure of Sm2O3, were investigated. For the gas sensing characterization, thick films were prepared with the as-prepared Sm2O3 microspheres. The gas sensing performance of Sm2O3 sensor devices was enhanced when gold electrodes were used. Transient impedance measurements revealed a reproducible and reliable detection of carbon dioxide and carbon monoxide at 400°C. The increase of the applied frequency produced stable and noiseless graphs. Furthermore, quantitative detection of the test gases was revealed by impedance and polarization measurements.

WO3 nanomaterials synthesized via a sol-gel method and calcination for use as a CO gas sensor

Carbon monoxide is a poisonous and hazardous gas and sensitive sensor devices are needed to prevent humans from being poisoned by this gas. A CO gas sensor has been prepared from WO3 synthesized by a sol-gel method. The sensor chip was prepared by a spin-coating technique which deposited a thin film of WO3 on an alumina substrate. The chip samples were then calcined at 300, 400, 500 or 600 °C for 1 h. The sensitivities of the different sensor chips for CO gas were determined by comparing the changes in electrical resistance in the absence and presence of 50 ppm of CO gas at 200 °C. The WO3 calcined at 500 °C had the highest sensitivity. The sensitivity of this sensor was also measured at CO concentrations of 100 ppm and 200 ppm and at operating temperatures of 30 and 100 °C. Thermogravimetric analysis of the WO3 calcined at 500 °C indicated that this sample had the highest gas adsorption capacity. This preliminary research has shown that WO3 can serve as a CO gas sensor and that is should be further explored and developed.

CO Sensor Using ZnO Thin Film Derived by RF Magnetron Sputtering Technique

In this paper, the fabrication and results of zinc oxide (ZnO) thin-film CO gas sensor are discussed. The thin film of c-axis oriented ZnO is deposited on Si/SiO2 substrate at room temperature using RF magnetron sputtering technique. The deposited ZnO film is annealed at different temperatures starting from 200 °C to 400 °C. The crystalline structural properties are analyzed by X-ray diffraction technique and the preferred orientation of ZnO thin film (along 002 direction) is found at 400 °C. Further, ZnO thin film is characterized by scanning electron microscopy and surface profilometer to analyze the surface properties and thickness. The deposited ZnO film is supported by Au electrodes and Pt microheater to couple the sensing signal with outer circuitry. A measurement system is also developed to measure the gas sensing properties and the results are discussed in detail.

Low Power Consumption CO2 Gas Sensor Using Ionic Liquid

Recently, various gas sensors are investigated. Specially, CO2 gas sensor is worthy of the notice, because monitoring of CO2 gas concentration is important for energy-saving. For example CO2 gas concentration is required for 1000 ppm or less in space, such as office buildings, a building management method, a production plant, and an IT-related server room. An exhaust gas periodically compulsory in order to make the present condition and CO2 gas concentration below into a steady value. By minimizing the displacement volume of the air which is carrying out air-conditioning management using CO2 sensor, an air-conditioning system carries out efficient operation, and it aims at development of CO2 sensor corresponding to the low consumption power high integration interlocked with a sensor network system efficiently. However the conventional CO2 gas sensors have the following problems, 1) large power consumption, 2) large size and 3) long detection time. These problems are mainly caused by usage of a light source and heater. We are interested in the ionic liquids because the ionic liquids are 1) the conductivity is high at room temperature, 2) thermal and chemical property is high stable, 3) volatility is high and 4) adsorb polarity molecule gases as like CO2, NH3, SO2, and NO2. Therefore we develop CO2 sensor which converted CO2 concentration into ionic liquid which adsorbed CO2 specifically by impedance. Our sensor feature is that it isn't used light source and heater, it is used ionic response. It compares with conventional CO2 sensor, 1) low consumption power, 2) miniaturization, 3) high-speed response and 4) low consumption CO2 gas sensor using ionic liquids. We use ionic liquids of imidazolium salts, EMIMBF4, EMIMTFSI and DEMEBF4. The impedance of ionic liquids decreases along with increase of CO2 gas concentration. By measuring the impedance of ionic liquids, we can estimate CO2 gas concentration of the atmosphere. From the experiment, measurement resolution of CO2 gas concentration was 100 ppm. The power consumption of our proposed CO2 gas sensor is several tens of microwatts, and this value is 1/1000 smaller compared with conventional CO2 gas sensors (NDIR and Solid state electrolyte cell).

Carbon dioxide resistive sensor based on titanium oxide nanowires doped with potassium

Potassium-doped titanium oxide (TiO2) nanowires are fabricated by the moisture-assisted, direct oxidation of a thin film of titanium at 650°C. The influence of the fabrication conditions on the structure and morphology of the nanowires was investigated. It was shown that the presence of potassium (K) is necessary for the formation of the nanowires. The density of growth of the nanowires was high, and the lengths of the nanowires were tens of micrometres. The K-doped TiO2 nanowires showed the possibility of use as a sensing material because of their significant and consistent response to responding to carbon dioxide (CO2) gas. In addition, H2 plasma treatment improved the sensitivity of the CO2 gas sensor made of K-doped TiO2 nanowires. Although the sensing mechanism is not clear, this development suggests opportunities for the fabrication of simple and inexpensive CO2 microsensors with low power consumption.

Response characteristics of a potentiometric CO2 gas sensor based on Li3PO4 solid electrolyte using Au film as the electrodes

A potentiometric CO2 gas sensor based on Li3PO4 film with the thickness of 0.8 μm prepared by thermal evaporation method was developed. Au thin film with the thickness of 400 nm deposited by sputtering method was used as the metal electrodes of the sensor. Li2CO3 and Li2TiO3 with 10 mol. % TiO2 were used as the sensing and reference electrodes by screen printing the materials on the Au thin film electrodes, respectively. Response characteristics of the sensor to CO2 in the range of 250 ppm to 5000 ppm at different working temperatures were investigated. The electromotive force (EMF) values of the sensor were linearly dependent on logarithm of CO2 partial pressure at the temperatures between 420 °C and 530 °C. Dependence of response and recovery time, initial EMF, ΔEMF/dec on working temperature was presented. It can be found that the response time and recovery time reduced with the enhancement of working temperature and gradually reached to the limit when the temperature is above 500 °C. However, the maximum ΔEMF/dec value was obtained at the temperature of 440 °C. The dependence of ΔEMF/dec on working temperature was newly found and different from previous research. The results suggest potential use of thin film metal electrodes in solid electrolyte gas sensors for lower temperature and miniature applications.

Gas Sensors Fabricated by Aerosol Deposition

Zinc oxide (ZnO) is a low toxicity and environmentally friendly material, and it is applied on devices, sensors or actuators for trending towards green-life. A porous ZnO film deposited by a rapid process of aerosol deposition (AD) was employed as the gas-sensitive material in a CO gas sensor for reducing the manufacturing cost and time, further extending the AD application. A relative resistance change (R / R) of the ZnO gas sensor was used for CO gas measurement. The sensitivity of the fabricated ZnO gas sensors had a more outstanding performance about 49%, compared to the literature data reported by Joshi.

CO gas-sensing properties of CuO-TiN and CuO-TiO2 prepared via an oxidizing process of a Cu-TiN composite synthesized by a mechanically induced gas-solid reaction

A Cu-TiN composite powder was synthesized by ball milling a Ti2Cu alloy for 25 h in an N2 pressurized atmosphere for use in CuO-TiN and CuO-TiO2 p-type sensing materials. The sensing materials were prepared via a two-step oxidizing process following an investigation of their CO gas-sensing properties. The resistances of both sensing materials increased as CO was introduced, which is typical for a p-type semiconductor at temperature higher than 200 °C. It was found that the CuO-TiN powder shows a better response above 200 °C when compared to the CuO-TiO2 powder. The highest response shown by CuO-TiN was 3.18, while CuO-TiO2 shows a response of 2.20 for 1000 ppm of CO gas at 250 °C. It is believed that the lower responses of CuO-TiO2 at temperature higher than 200 °C was due to the falloff of p-type resistances by simultaneous operation of p- and n-type semiconductors in the presence of CO gas.

Effect of an Au Nanodot Nucleation Layer on CO Gas Sensing Properties of Nanostructured SnO2 Thin Films

Effect of an Au Nanodot Nucleation Layer on CO Gas Sensing Properties of Nanostructured SnO2 Thin Films

Lanthanum Dioxide Carbonate La2O2CO3 Nanorods as a Sensing Material for Chemoresistive CO2 Gas Sensor

Lanthanum dioxide carbonate La2O2CO3 nanorods with high crystallinity were successfully prepared from La(OH)3 nanorods. The structural and morphological characterizations of the products were performed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS). La(OH)3 nanorods were shape-preserved transformed to La2O2CO3 nanorods at 400 oC for 2h. TEM images indicate that the as-obtained La2O2CO3 entirely consists of uniform nanorods in high yield with diameter of 13-15nm and length of 100-150nm. The indirect-heating sensor using La2O2CO3 nanorods as sensitive material was fabricated on an alumina tube with Au electrodes and platinum wires. The sensing properties of the sensor based on La2O2CO3 nanorods were investigated. It is shown that the sensor exhibits high gas response for CO2 gas at operating temperature of 325oC, making it to be potential candidate for practical detectors for CO2 gas.

Al-doped ZnO for highly sensitive CO gas sensors

Al-doped ZnO (AZO) nanoparticles have been prepared using a modified sol–gel technique. The as-prepared AZO nanoparticles were annealed at 400°C, and their morphologies and microstructural characteristics were investigated using transmission electron microscopy (TEM) and x-ray powder diffraction (XRD) analyses. Crystallites with an average size of approximately 60–70nm and ZnO as a primary phase were observed in all samples. In addition, smaller nanoparticles (less than 5nm) with an Al-rich structure covering the surface of larger ZnO crystallites were also noted on the Al-doped samples.Chemoresistive devices consisting of a thick layer of AZO nanoparticles on interdigitated alumina substrates have been fabricated, and their electrical and sensing characteristics for carbon monoxide were investigated. Al-doping provided a remarkable decrease in the electrical resistance of the sensing layer at the working temperature of the sensors (250–300°C). The sensors based on Al-doped ZnO exhibited a higher response than the pure ZnO sample, allowing the detection of CO at sub-ppm concentrations in air. The enhancement in sensing properties was discussed in terms of the characterization and electrical data.

Modified Transport Properties Of LiNbO3 Dispersed Li2CO3 Composite System For Electrochemical CO2 Sensor

In the present investigation, LiNbO3 dispersed Li2CO3 composite of varying volume fraction is prepared. Its validity of placement in ionic conductor is verified by determining ionic transference number by Wagner’s dc polarization technique and bulk electrical conductivity is estimated with complex impedance spectroscopy. Two different conduction mechanisms are revealed by the complex impedance plots at low and high frequencies. Significant enhancement in the ionic conductivity has resulted due to enhancement in vacancies at the grain boundary interface facilitated by the localized polarization of carbonate grains due to the presence of ferroelectric phase. The effect on electrode kinetics is studied by characterizing an electrochemical CO2 gas sensor with this composite as sensing electrode which showed significant reduction in response time and recovery time (<10 sec). The use of such composite systems will benefit the development of fast electrochemical devices.

Research on a Highly Sensitive Magnetic-Catalytic CMOS-MEMS Compatible Gas Sensor

This letter proposes a new magnetic-catalytic sensing mechanism designed to increase the sensitivity of a gas sensor with mesh-stacked sensing electrodes. Beyond the conventional power dissipation of heating to maintain a certain working temperature, the novel gas sensor with a magnetic-catalytic mechanism operates at an ambient temperature, and heating power does not need to be considered. The standard 0.35 μm CMOS process was used to fabricate a gas sensor with mesh-stacked electrodes. To prepare the magnetic sensing material, a SnO2 solution, prepared using the sol-gel method, was mixed with Fe3O4 at a ratio of SnO2:Fe3O4=3:1 and was deposited onto mesh-stacked electrodes. When the CO gas sensor was introduced, the sample was tested and verified inside a CO gas chamber using a magnetic field generator composed of solenoidal coils. According to a careful investigation of the measurement results, the highest sensitivity, 1.73%/ppm, was obtained under 12 G in a horizontal magnetic field, indicating that the mechanism is applicable for use in an ultralow power chemical microsensor with high sensitivity.

CO2 Gas Sensor Based on MIS Structure with LaF3 Layer

Abstract The aim of this research is to find a CO 2 sensor with high value of the response to CO 2 concentrations in a range of several hundreds of ppm. The sensor investigated in this work is based on metal/solid electrolyte/insulator/silicon structure with fluorine conducting solid electrolyte LaF 3 layer. It is characterized by rather with short response and recovery time of about 1 min (t 90 ) at room temperature. The application of such gas sensor seems to be very promising for the measurement of CO 2 concentration in a range from atmospheric background (300 ppm) to maximum permissible concentration (2000 ppm).

Gold-catalytic green synthesis of Cu2O/Au/CuO hierarchical nanostructure and application for CO gas sensor

Hierarchical Cu2O/Au/CuO nanostructures have been achieved by water-based green fabrication at a low temperature. Precluding the requirement of the template removal, the generation of hierarchical architecture relied on the catalytic activity of gold nanoparticles attached on the Cu2O nanocubes. Notably, we creatively developed the dual-roles catalytic ability of gold, which not only remarkably increased the specific surface area of this architecture, but also provided the enhanced performance for gas sensing.

Effective decoration of Pd nanoparticles on the surface of SnO2 nanowires for enhancement of CO gas-sensing performance

Decoration of noble metal nanoparticles (NPs) on the surface of semiconducting metal oxide nanowires (NWs) to enhance material characteristics, functionalization, and sensing abilities has attracted increasing interests from researchers worldwide. In this study, we introduce an effective method for the decoration of Pd NPs on the surface of SnO2 NWs to enhance CO gas-sensing performance. Single-crystal SnO2 NWs were fabricated by chemical vapor deposition, whereas Pd NPs were decorated on the surface of SnO2 NWs by in situ reduction of the Pd complex at room temperature without using any linker or reduction agent excepting the copolymer P123. The materials were characterized by advanced techniques, such as high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The Pd NPs were effectively decorated on the surface of SnO2 NWs. As an example, the CO sensing characteristics of SnO2 NWs decorated with Pd NPs were investigated at different temperatures. Results revealed that the gas sensor exhibited excellent sensing performance to CO at low concentration (1–25ppm) with ultrafast response-recovery time (in seconds), high responsivity, good stability, and reproducibility.

Potentiometric carbon dioxide sensor based on thin Li3PO4 electrolyte and Li2CO3 sensing electrode

Potentiometric CO2 gas sensors with thin-film lithium phosphate (Li3PO4) electrolytes were developed by using radio frequency (RF) magnetron sputtering. Li2CO3 and a mixture of Li2TiO3 and TiO2 were used as sensing and reference electrodes, respectively. By using the RF sputtering deposition process, we obtained a dense, crystalline, thin-film Li3PO4 electrolyte with good adhesion on the Al2O3 substrate. The thin-film Li3PO4 electrolyte had good ionic conductivity, i.e., 2.15 × 10−6 S cm−1 at 500 °C, and its activation energy was 0.97 eV. The thin-film Li3PO4 electrolyte was suitable for the miniaturization of potentiometric CO2 sensors. The thin-film potentiometric CO2 sensor provided relatively good sensing response for overall CO2 concentrations (500 to 3,000 ppm and 5 to 20 %) at 500 °C. The Nernstian slope of 78.2 mV/decade obtained for CO2 concentrations from 5 to 20 % at 500 °C was close to the theoretical value (76.6 mV/decade). Although the sensor’s reading deviated from the theoretical value at low CO2 concentrations (500 to 3,000 ppm), the sensor provided better sensing performance than a potentiometric CO2 sensor with a thick electrolyte. As a result, it was assumed that the thin-film sensor could be used to monitor the overall concentration of CO2 in the environment.

Semiconductor-Type MEMS Gas Sensor for Real-Time Environmental Monitoring Applications

Low power consuming and highly responsive semiconductor-type microelectromechanical systems (MEMS) gas sensors are fabricated for real-time environmental monitoring applications. This subsystem is developed using a gas sensor module, a Bluetooth module, and a personal digital assistant (PDA) phone. The gas sensor module consists of a NO2 or CO gas sensor and signal processing chips. The MEMS gas sensor is composed of a microheater, a sensing electrode, and sensing material. Metal oxide nanopowder is drop-coated onto a substrate using a microheater and integrated into the gas sensor module. The change in resistance of the metal oxide nanopowder from exposure to oxidizing or deoxidizing gases is utilized as the principle mechanism of this gas sensor operation. The variation detected in the gas sensor module is transferred to the PDA phone by way of the Bluetooth module.

PdO Nanoflake Thin Films for CO Gas Sensing at Low Temperatures

We prepared PdO nanoflake thin films by reactive sputter deposition and studied their gas-sensing response to CO at temperatures below 250 °C. The PdO thin film, which has a large open surface area allowing for rapid and extensive CO adsorption, exhibits a complicated CO sensing behavior. At temperatures below 150 °C, the electrical conductance of the thin film drops upon the exposure of the CO/dry air gas mixture. The CO sensing mechanism in this temperature range is described by the oxygen ionosorption model. At 150 °C, oscillatory response occurs when the CO concentration is larger than 2000 ppm. The oscillatory response is due to the reactivity switching between the PdO reduction and reoxidation reactions. In addition, the PdO thin film shows a rapid increase in the conductance before and after the oscillatory response regime. The conductance increase is ascribed to the positive charge accumulation at the interface between the PdO thin film and metal Pd nanoislands, which are formed during the PdO reduction. At temperatures higher than 150 °C, the conductance drops when the PdO thin film is exposed to CO. Besides the ionosorption model, the oxygen vacancy model is used to account for the CO sensing response of the thin film in the high-temperature range. On the basis of the inverse change in the CO sensing sensitivity at 150 °C, a CO sensor of high selectivity, which integrates two PdO sensing elements operating independently at 150 °C and a lower temperature, is proposed.