Solid-state Gas Sensors Research Articles

An amperometric solid-state NO 2 sensor with a solid polymer electrolyte and a reticulated vitreous carbon indicator electrode

Reticulated vitreous carbon (RVC) was tested as a material for the preparation of the indicator electrode in solid-state gas sensors. The test planar sensor contained a RVC indicator, a platinum auxiliary and a Pt/air reference electrode, with a solid polymer electrolyte (SPE) of 10% PVC, 3% tetrabutylammonium hexafluorophosphate (TBAHFP) and 87% of 2-nitrophenyloctyl ether (NPOE). The analyte, gaseous nitrogen dioxide in air, was monitored by reduction at −500 mV vs. the Pt/air electrode. The reduction current was linearly dependent on the analyte concentration over the whole test range, from 0.2 to 2.2 ppm (v/v). The sensitivity of determination amounted to 277 nA/ppm, the limit of detection was 80 ppb (at a relative humidity, RH, of 54%) and 90% of the steady-state signal was attained within 19 s. The measuring sensitivity depended on the temperature, the gas flow rate and the RH with slopes of 1.04% per 1°C, 32% per 1 ml/s and 0.16% per 1% RH, respectively. It has been demonstrated that RVC can successfully replace noble metals in gas solid-state sensors.

Memory effect and its switching by electric field in solid-state gas sensors

The Au/n-SnO 2/SiO 2/p-Si/Al heterostructures were grown using aerosol-gel and spray pyrolysis methods. The effect of capacitance memory was discovered in the presence of polar gas molecules: C 2H 5OH, NH 3, H 2O. The mechanism of gas sensitivity, capacitance memory and its switching was associated with the process taking place on the SnO 2/SiO 2 interface.

Materials for solid-state gas sensors

The major problems in the development of inorganic gas-sensor materials are discussed. The general principle of semiconductor gas sensors is considered, and the band-structure parameters sensitive to the gas-phase composition are determined. Ways of improving sensor selectivity are examined. The composition, microstructure, and gas sensitivity of nanocrystalline SnO2 and ZnO are investigated. The dopant content and grain size of Ni-doped SnO2 are optimized for H2S detection. The prospects of employing systems of two or more nanocrystalline oxides (nanocomposites) for gas detection are discussed

SO2 gas sensor utilizing stabilized zirconia and sulfate salts with a new working mechanism

A solid-state gas sensor for sulfur dioxide with a new working mechanism was fabricated and its sensing properties investigated. The sensor was constructed using yttria-stabilized zirconia as the oxygen ion conductor, silver sulfate based salts as the auxiliary phase, a silver sensing electrode and a platinum reference electrode. When sulfur dioxide was detected, the potential of the sensing electrode changed to negative with the new working mechanism. The 90% response time of the sensor to 100 ppm SO2 was ca. 40 s at 600°C, and the electromotive force (EMF) value obtained was perfectly linear to the logarithm of SO2 concentration over a wide range (1 to 1000 ppm). The Nernst’s slope corresponded exactly to the theoretical value based on a two-electron electrochemical reaction.

Integrated solid-state gas sensors based on SnO 2(Pd) for CO detection

Thin films of polycrystalline Pd-doped tin dioxide SnO 2(Pd), widely used as sensitive element in gas sensors devices for atmospheric pollutant as CO, have been deposited on Si substrates through the ultrasonic aerosol pyrolysis technique. It is firstly shown that the sensitivity S=( G− G 0)/ G 0 to CO at low temperature (80–120°C), measured on steady state regime by conductance–temperature characteristics, depends on the concentration x of Pd incorporated into the film and on the SnO 2 grain size D. The highest sensitivity S corresponds to a very sharp ( x, D) domain. Secondly, the films synthesised under these optimal conditions have been integrated to a silicon-based prototype of micro-sensor. This device provides stable response in dynamic regime ( S=17) at low temperature (∼100°C) to 50 ppm CO by using a short-term annealing ( T annealing=350°C, t annealing=5 min) before each measurement.

5841021 Solid state gas sensor and filter assembly : De Castro Emory S; Genders J Davi; Weinberg Norman L Nahant, MA, United States

5841021 Solid state gas sensor and filter assembly : De Castro Emory S; Genders J Davi; Weinberg Norman L Nahant, MA, United States

Study of the interferences of NO 2 and CO in solid state commercial sensors

Commercial solid state gas sensors have been used to measure NO 2 and CO concentrations in the range of the first alarm thresholds for urban environments. Their mutual interference has been studied at three operating temperature ranges. The results showed that different sensitivities and selectivities can be obtained with the same type of sensors. This fact is used to make a multisensorial system based on commercial solid state gas sensors. Using artificial neural networks analysis, we detect the presence of NO 2 and CO gases, and even measure the concentration of both gases with a sufficient accuracy.

SO x solid state gas sensors: A review

The performance of any solid state electrochemical gas sensor is always rated on its response time, thermodynamic stability, operating temperature, gas sensing ability, sensitivity and gas concentration range which is sensed. Here, we have reviewed the factors contributing towards a gradual development of electrochemical solid state SO x sensor in terms of a continuous tailoring of its two basic components, i.e. solid electrolyte and reference electrode with high ionic and mixed (ionic + electronic) conductivities, respectively.

Nafion-based solid-state gas sensors: Pt / Nafion electrodes prepared by an impregnation-reduction method in sensing oxygen

The influences of the reductant concentration of NaBH4 and the quantity of Pt loading on the active surface area and the sensitivity of the Pt/Nafion electrodes prepared by an impregnation-reduction method in detecting oxygen were investigated in this study. The Pt/Nafion electrodes with a Pt loading of 4.99 mg/cm2, obtained at 0.0107 M Pt(NH3)4Cl2 and 0.06 M NaBH4, show maximum sensitivities of 0.0528 A/ppm and 0.0538 A/ppm obtained in O2 concentration regions of 0–5000 and 5000–50 000 ppm, respectively. A sensing model was also proposed to illustrate the sensing phenomenon.

Stability and oxidation of the sandwich type gas sensors based on thin metal films

Abstract The stability of the properties is investigated in the new family of the solid-state gas sensors based on various thin metal films (Pt, Au, Ni, Mo) with the modifying top layer of tin oxide. The resistance response to exposure to gas is demonstrated being stable within certain interval of temperatures. The limits of the interval depend on the metal selected for the basic layer. The variation of the chemical composition is also studied in the sensors after overheating in the clean or contaminated air. The drift of the electric resistance and the mechanism of gas sensitivity are discussed on the basis of the oxidation of the metal film.

Comparison of light emission from room temperature light emitting diodes with InAs active regions grown by LPE

InAs and InAsSbP are promising materials for the fabrication of mid-infrared light sources for use in solid state gas sensors. In this paper, we report work on n-i-p and p-i-n. InAs light emitting diode structures grown using liquid phase epitaxy (LPE) on InAs substrates. These homoepitaxial diodes were compared to double heterojunction InAsSbP/InAs LEDs with InAs active regions. Room temperature emission at wavelengths between 3.3 µm and 3.7 µm (dependent on structure) was readily obtained. Electroluminescence spectra of these devices are presented, and a comparison with photoluminescence spectra of the epitaxial material is used to determine the region of the diode giving rise to the light emission. At room temperature, in the double heterojunction LEDs, the light emission was observed to originate from the InAs active region. However, in the homoepitaxial LEDs, the light was generated both in the undoped and p+ regions of the device, depending on the precise structure.

Vitality protection solid-state gas sensors based on macrocyclic cobalt(III) complexes

The electrochemical low-cost sensors for the quantitative analysis of toxic and explosive gases in workplace air are being reported. The sensors are of voltammetric (galvanic) type based on proton conductive solid-state electrolyte with high conductivity at an ambient temperature and are fabricated as pellets with the dimensions 12 × 5 mm. The implementation of macrocyclic cobalt(III) complexes with different ligands as the counter electrode materials allows the development of the sensors with good output linearity, stability and high selectivity towards the gases measured, and long operating lifetime, up to several years.

Hydrogen sensor based on antimonium pentoxide-phosphoric acid solid electrolyte

A solid composite electrolyte with high proton conductivity based on antimonium pentoxide with additives of phosphoric acid has been obtained. A potentiometric solid-state gas sensor using this electrolyte has been developed for detecting small amounts of hydrogen (10–2000 ppm) in gas mixtures at ambient temperature. The sensor consists of the reference electrode: Ag or Ag/(Ag + Ag 2SO 4), the solid composite electrolyte and H 2-sensitive electrode: Pt or Pd. The electromotive force (e.m.f.) of the sensor varies logarithmically with H 2 concentration for hydrogen partial pressures in the range 100–2000 ppm and depends on the oxygen partial pressure. The slope of e.m.f.-log( pH 2) dependence is 170 and 200 mV for Pt and Pd, respectively, which exceeds the Nernst value, presumably due to the formation of a mixed potential. The sensor can operate at a wide range (20–95%) of a relative humidity.

Precise measurement of methane in air using diode-pumped 3.4-μm difference-frequency generation in PPLN

volume multi-pass absorption cell with an 18-m path length. The methane mixing ratio was determined by comparing the direct optical absorption measured in the sample with that measured in a reference gas at 100 torr and room temperature. Relative accuracy of better than 1 ppb (parts in 109, by mole fraction) was achieved in measurements of natural air that contained 1700–1900 ppb methane. The typical measurement time for each sample was 60 seconds. The accuracy was limited by residual interference fringes in the multi-pass cell that resulted from scattering. Without the use of reference samples, the relative accuracy was 20 ppb; it was limited by the long-term reproducibility of the spectroscopic baseline, which was affected by drift in the optical alignment coupled to changes in the ambient temperature. This work demonstrates the use of diode-pumped difference-frequency generation (DFG) in PPLN in a high-precision infrared spectrometer. Compact, room-temperature solid-state gas sensors can be built based on this technology, for accurate real-time measurements of trace gases in the 3–5 μm spectroscopic region.

Nernstian and non-nernstian potentiometry

It is possible to perform a potentiomeric measurement in the gas phase in such a way that the formation of charge transfer complex between the gaseous species and semiconducting electrode results in chemical modulation of the Fermi level. In such a case the functional relationship is a generalized form of the Nernst equation in which the slope of the dependence of measured potential on partial pressure of gas assumes fractional values. It is shown that an entire new class of solid state gas sensors can be based on this principle.

Optical recognition of CO and H2 by use of gas-sensitive Au–Co3O4 composite films

M. Ando, T. Kobayashi, S. Iijima and M. Haruta, J. Mater. Chem., 1997, 7, 1779 DOI: 10.1039/A700125H

Optimized temperature-pulse sequences for the enhancement of chemically specific response patterns from micro-hotplate gas sensors

Microfabricated solid-state gas sensors have been of continuing interest because of the potential for arrays of devices with low power consumption. Devices based on a micromachined ‘hotplate’ offer the additional advantage of a wide operating temperature range with a rapid thermal time constant of order 1 ms. By operating the device in a temperature-programmed mode, reaction kinetics on the sensing film surface are altered, producing a time-varying response signature that is characteristic of the gas being sensed. Approaches to optimizing such temperature programs to maximize the differences in response signatures for gases of interest or to enhance the sensitivity of the device are discussed.

An automatic low-level gas blender

The design and construction of a new automated low-level gas mixing apparatus is described which is intended for use in the testing and characterisation of solid-state and other gas sensors. This apparatus will blend gases such as carbon monoxide with clean air to produce mixtures of 1 to 1000 parts per million and is based upon the volume proportioning principle, where a gas sample is prepared by mixing a pre-determined volume of pure gas with a known volume of clean air. The instrument is capable of producing repeatable gas mixtures at a series of specified concentrations with accuracies better than ±0.5% for the low range (1-100 ppm) and ±0.2% for the high range (100-1000ppm) as compared with concentrations measured using two calibrated commercial monitors.

Physics, Chemistry & Technology of Solid State Gas Sensor Devices

Physics, Chemistry & Technology of Solid State Gas Sensor Devices

Development and testing of a solid-state CO 2 gas sensor for use in reduced-pressure environments

A planetry instrument called the thermal and evolved analyzer (T/EGA) is currently being developed, consisting of a combined differential scanning calorimeter (DSC) and evolved gas analyzer (EGA) to subject regolith samples to a temperature ramp and monitor gas-evolution events. This paper reports the development and testing of a miniature carbon dioxide (CO 2) solid-state electrochemical gas sensor (SSEGS) for use in the EGA portion of the instrument. A miniature potentiometric CO 2 sensor has been developed that is configured in a planar geometry. The sensor uses solid-state reference and measuring electrodes co-located one one side of a beta alumina electrolyte substrate, and a thick-film platinum heater on the opposite side. Experiments are performed under reduced-pressure conditions to characterize the sensor response in terms of heater power, sensor temperature, total pressure, and gas-composition parameters. The sensor response to carbon dioxide (CO 2) is found to be a complex function of these variables, and to act through two separate and independent mechanisms to influence the sensor output. The sensor oxygen sensitivity is also measured in the presence of CO 2. A sensor temperature of 530°C is found to result in an oxygen-response slope coefficient of zero. Operation of the sensor at this temperature results in selective carbon dioxide response, and an output that is independent of oxygen partial pressure.