Detection Of H2 Research Articles

High response and low concentration hydrogen gas sensing properties using hollow ZnO particles transformed from polystyrene@ZnO core-shell structures

High quality, closely packed nanorods (NRs) textured ZnO hollow particles were prepared via thermal treatment of polystyrene@ZnO core-shell structures at 300 °C. Polystyrene@ZnO core-shell structures were synthesized using a chemical route. These hollow ZnO particles were investigated for hydrogen gas sensing properties. Morphological properties were studied using field emission scanning electron microscope (FE-SEM). Structural parameters and molecular fingerprint confirmation were carried out by x-ray diffraction (XRD) and Raman analysis respectively. The elemental compositions and atomic species of sensor materials were studied using energy dispersive spectrometer (EDS) analysis and x-ray photoelectron spectroscopy (XPS) spectra respectively. The study of atomic planar arrangements and crystalline nature were examined by using a high-resolution transmission electron microscope (HR-TEM) micrograph and selected area electron diffraction (SAED) pattern respectively. Hollow ZnO particles sensor was revealed remarkable selectivity towards hydrogen (H2) gas. The lowest H2 detection limit of ZnO sensor was at 2 ppm with the response of 7%, whereas 89% gas response was recorded for 100 ppm at optimized temperature 225 °C with response time 139 s. Gas response as a function of operating temperatures as well as gas concentrations was tested along with good sensor stability. The transient gas response and selectivity studies were carried out and analyzed. ZnO growth and gas sensing mechanisms were elucidated.

Hydrogen sensing performance of atmospheric plasma sprayed tin dioxide coating

Abstract As a potential source of clean energy, hydrogen (H2) is considered as a promising fuel for internal combustion engines. Being colorless, odorless, and highly explosive gas; detection of H2 using a cost effective sensor is important. In the present work, atmospheric plasma sprayed (APS) tin dioxide (SnO2) coating on alumina substrate was used for hydrogen (H2) sensing. For steam reforming of ethanol, its decomposition on metal surface leads to the formation of CH4 and CO as well. Therefore, sensing characteristics of plasma sprayed SnO2 coating were also investigated for carbon monoxide (CO) and methane (CH4) gases. The plasma sprayed coating exhibited satisfactory H2 sensing characteristics in terms of response %, response time, and repeatability over elongated duration. Up to 250 °C, SnO2 coating was found to be insensitive towards CH4 sensing and cross sensitive only to CO gas. Assuming Langmuir adsorption isotherm we have fitted the conductance transients of H2 and CO to estimate the heat of adsorption (Q) and activation energy (Ea) as a function of concentration for these gases. Irrespective of the test gas concentration, the estimated activation energy towards H2 sensing was lower as compared to that of CO. As compared to CO, the higher response % of SnO2 sensor towards H2 sensing was explained to be due to its lower activation energy of adsorption. To the best of authors’ knowledge, this is the first report highlighting the H2 sensing performance of plasma sprayed SnO2 coating. We have proposed that atmospheric plasma sprayed large area SnO2 coating can be utilized as a catalyst in ethanol reforming process together with the detection of H2, CO and CH4 gases as reaction products.

Enhancement mechanism of H2 sensing in metal-functionalized GaN nanowires

We use density functional theory to evaluate the metals adsorption on the surface of Gallium Nitride (GaN) nanowire (NW) and propose a model to explore H2 sensing enhancement mechanism of metal-functionalized GaN nanowire in theory. The adsorption energy is negative when the metal atoms move closed to the surface of GaN NWs, which reflect the feature of exothermic reaction. Moreover, the simulation indicate the metal-functionalized GaN have much stronger sensing to H2 by forming chemisorption between H2 molecules and metal atoms on the surface, rather than the conventional van der Waals forces between H2 molecules and the pure GaN surface. The latter can only lead to a poor response to H2 since the weak interactions. Comparing with Au, Ag and Cu-functionalized surface, H2 molecules are adsorbed at Pt-functionalized surface, with the lowest adsorption energy, which indicate it is expect to be the most suitable for H2 detection. It should be originated from the largest band gap change and most significantly surface charge reconstruction of Pt-functionalized surface. Our results present an enhancement mechanism of gas sensing from the reduction of the surface potential by the metals effect, which can be applied to design and advance gas-sensing materials.

Hot Charge Carriers in Quantum Dots: Generation, Relaxation, Extraction, and Applications

AbstractThis article discusses the hot charge carriers in semiconductor quantum dots (QDs): their generation, relaxation, extraction and applications in different technologically relevant areas. It has been reported that the most common ways to generate hot charge carriers are photo‐excitation by energy more than the band gap energy. However, recently the other means to generate hot charge carriers such as doping, and semiconductor plasmon interaction have also been evolved and their advantages over the conventional method have been discussed. Relaxation dynamics of hot charge carriers and different processes related to this such as multiple exciton generation, Auger recombination, phonon vibrations and ligand assisted charge carrier relaxation are mentioned. It was shown that the relaxation mechanism of hot charge carriers (both hot electron and hot hole) follow different pathways and either of the mechanism is playing a role depending on the QDs structure and the surrounding conditions. Studies pertaining to interaction of QDs with other semiconductors, metal nanoparticles or with different molecular adsorbates suggest that the hot charge carrier extraction is possible in these heterojunctions with extraction time in sub‐ps scale. Application of hot charge carriers in different fields such as photovoltaics, photo‐catalysis, infrared detectors, and H2 detection have been shown and it was observed that the efficiency of the above‐mentioned processes is much higher when the hot charge carriers are involved, suggesting their importance in these areas.

UV-activated gold decorated rGO/ZnO heterostructured nanocomposite sensor for efficient room temperature H2 detection

Extended surface area in addition to higher conductivity and abundant free electrons/holes generation has been key players for any efficient sensor design. Therefore, contribution from graphene as highest conductive material and plasmonics from gold (Au) were expected to facilitate efficient zinc oxides (ZnO) nanostructures-based Hydrogen gas detection. We have presented herewith a facile route to synthesize ZnO nanosheets from elongated nanoblocks of the same in presence of reduced graphene oxide (rGO) under laser ablation environment. Au decorated such rGO/ZnO heterostructured nanosheets were found to be highly selective and sensitive to H2 detection under ultraviolet radiation at room temperature (RT). A detailed investigation was carried out to confirm topographic evolution through high resolution scanning electron microscopy. Optical band gap and infrared absorption of as-synthesized specimens at different stages were investigated further in addition to structural confirmation using X-ray diffraction analysis. Raman spectroscopy, a complementary technique was utilized to investigate the specimens at different stages too. SEM-aided elemental analysis inferred that gold nanoparticles were homogeneously distributed over the rGO/ZnO heterostructure. A custom-made setup designed at our disposal were utilized to understand the selectivity and sensitivity of as-fabricated heterostructure for H2 detection. The H2 gas sensing properties of Au nanoparticles decorated rGO/ZnO heterostructure were investigated at RT under UV irradiation and compared with those observed using pristine ZnO nanostructure at high working temperature. A plausible mechanism was illustrated with reference to well-known ‘spell-over’ scenario usually observed in plasmonic sensors.

Evidence for diffuse molecular gas and dust in the hearts of gamma-ray burst host galaxies

Context. Damped Lyman-α (DLA) absorption-line systems at the redshifts of gamma-ray burst (GRB) afterglows offer a unique way to probe the physical conditions within star-forming galaxies in the early Universe. Aims. Here we built up a large sample of 22 GRBs at redshifts z > 2 observed with VLT/X-shooter in order to determine the abundances of hydrogen, metals, dust, and molecular species. This allows us to study the metallicity and dust depletion effects in the neutral interstellar medium at high redshift and to answer the question of whether (and why) there might be a lack of H2 in GRB-DLAs. Methods. We developed new methods based on the Bayesian inference package, PyMC, to FIT absorption lines and measure the column densities of different metal species as well as atomic and molecular hydrogen. The derived relative abundances are used to FIT dust depletion sequences and determine the dust-to-metals ratio and the host-galaxy intrinsic visual extinction. Additionally, we searched for the absorption signatures of vibrationally-excited H2 and carbon monoxide. Results. We find that there is no lack of H2-bearing GRB-DLAs. We detect absorption lines from molecular hydrogen in 6 out of 22 GRB afterglow spectra, with molecular fractions ranging between f ≃ 5 × 10−5 and f ≃ 0.04, and claim tentative detections in three additional cases. For the remainder of the sample, we measure, depending on S/N, spectral coverage and instrumental resolution, more or less stringent upper limits. The GRB-DLAs in our sample have on average low metallicities, [X/H]¯ ≈ −1.3, comparable to the population of extremely-strong QSO-DLAs (log N(H I) > 21.5). Furthermore, H2-bearing GRB-DLAs are found to be associated with significant dust extinction, AV > 0.1 mag, and dust-to-metals ratios DTM > 0.4, confirming the importance of dust grains for the production of molecules. All these systems exhibit neutral hydrogen column densities log N(H I) > 21.7. The overall fraction of H2 detections in GRB-DLAs is ≥ 27% (41% including tentative detections), which is three to four times larger than in the general QSO-DLA population. For 2 < z < 4, and considering column densities log N(H I) > 21.7, the H2 detection fraction is 60–80% in GRB-DLAs and in extremely strong QSO-DLAs. This is likely due to the fact that both GRB- and QSO-DLAs with high neutral hydrogen column densities are probed by sight-lines with small impact parameters, indicating that the absorbing gas is associated with the inner regions of the absorbing galaxy, where the gas pressure is higher and the conversion of H I to H2 takes place. In the case of GRB hosts, this diffuse molecular gas is located at distances ≳ 500 pc from the GRB and hence is unrelated to the star-forming region where the event occurred.

La3+ doped SnO2 nanofibers for rapid and selective H2 sensor with long range linearity

Catalytic lanthanum ions (La3+), beneficial for fast dissociative adsorption of hydrogen on its surface, were chosen and introduced into SnO2 nanofibers with different atomic molar ratio to Sn (AMR: 0.5%, 1.0% and 3%) via electrospinning and calcination technique. The sensitivity of LaSnO2 metastable solid solution nanofibers (LSMSSNs) for H2 detection is 9.9 against 100 ppm H2 at 300 °C, which is 2.5 times and 1.6 times higher than that of SnO2 nanofibers and La2O3@SnO2 p-n heterojunction nanofibers (LSPNHNs), respectively. More importantly, LSMSSNs achieved both rapid response and recovery behavior of ∼ 1s, long range detectable linearity from 1000 to 25,000 p.m. against H2 and good selectivity towards ethanol, toluene, carbon monoxide and butane, which is very useful for the practical application. A plausible sensing mechanism based on p-type La3+ doping has been established and the relationship with La2O3@SnO2 p-n heterojunction has been investigated. This work provides a basis for understanding and optimizing the high sensitive metal oxide based gas sensors.

Twofold Porosity and Surface Functionalization Effect on Pt-Porous GaN for High-Performance H2-Gas Sensors at Room Temperature.

The achievement of H2 detection, up to 25 ppm, at room temperature using sulfur-treated, platinum (Pt)-decorated porous GaN is reported in this study. This achievement is attributed to the large lateral pore size, Pt catalyst, and surface treatment using organic sulfide. The performance of H2-gas sensors is studied as a function of the operating temperature by providing an adsorption activation energy of 22 meV at 30 ppm H2, confirming the higher sensitivity of the sulfide-treated Pt–porous GaN sensor. Furthermore, the sensing response of the sulfide-treated Pt–porous GaN gas sensor increases with the increase in porosity (surface-to-volume ratio) and pore radii. Using the Knudsen diffusion–surface reaction equation, the H2 gas concentration profile is simulated and fitted within the porous GaN layer, revealing that H2 diffusion is limited by small pore radii because of its low diffusion rate. The simulated gas sensor responses to H2 versus the pore diameter show the same trend as observed for the experimental data. The sulfide-treated Pt–porous GaN sensor achieves ultrasensitive H2 detection at room temperature for 125 nm pore radii.

Au decoration of a graphene microchannel for self-activated chemoresistive flexible gas sensors with substantially enhanced response to hydrogen.

Graphene is one of the most promising materials for high-performance gas sensors due to its unique properties such as high sensitivity at room temperature, transparency, and flexibility. However, the low selectivity and irreversible behavior of graphene-based gas sensors are major problems. Here, we present unprecedented room temperature hydrogen detection by Au nanoclusters supported on self-activated graphene. Compared to pristine graphene sensors, the Au-decorated graphene sensors exhibit highly improved gas-sensing properties upon exposure to various gases. In particular, an unexpected substantial enhancement in H2 detection is found, which has never been reported for Au decoration on any type of chemoresistive material. Density functional theory calculations reveal that Au nanoclusters on graphene contribute to the adsorption of H atoms, whereas the surfaces of Au and graphene do not bind with H atoms individually. The discovery of such a new functionality in the existing material platform holds the key to diverse research areas based on metal nanocluster/graphene heterostructures.

Nano lily-buds garden like ZnO nanostructures based gas sensor for H2 detection

Nano lily-buds (NL-buds) garden like ZnO nanostructure synthesized by simple single step thermal decomposition method. XRD result confirmed the hexagonal (Wurtzite phase) crystal structure, and FESEM micrograph shows the formation of NL-buds like ZnO nanostructure. The chemical states and elemental composition of the elements were studied using XPS and EDS respectively. The maximum sensitivity ∼178 was recorded for ZnO sample at 180 °C for 80 ppm of H2 exposure with a fast response time of the order of ∼1–2 s. ZnO NL-buds sensor attained a reversible, and high response towards H2 gas signifying it as a potential candidate for H2 sensor application.

High‐Performance, Transparent Thin Film Hydrogen Gas Sensor Using 2D Electron Gas at Interface of Oxide Thin Film Heterostructure Grown by Atomic Layer Deposition

AbstractA high‐performance, transparent, and extremely thin (<15 nm) hydrogen (H2) gas sensor is developed using 2D electron gas (2DEG) at the interface of an Al2O3/TiO2 thin film heterostructure grown by atomic layer deposition (ALD), without using an epitaxial layer or a single crystalline substrate. Palladium nanoparticles (≈2 nm in thickness) are used on the surface of the Al2O3/TiO2 thin film heterostructure to detect H2. This extremely thin gas sensor can be fabricated on general substrates such as a quartz, enabling its practical application. Interestingly, the electron density of the Al2O3/TiO2 thin film heterostructure can be tailored using ALD process temperature in contrast to 2DEG at the epitaxial interfaces of the oxide heterostructures such as LaAlO3/SrTiO3. This tunability provides the optimal electron density for H2 detection. The Pd/Al2O3/TiO2 sensor detects H2 gas quickly with a short response time of <30 s at 300 K which outperforms conventional H2 gas sensors, indicating that heating modules are not required for the rapid detection of H2. A wide bandgap (>3.2 eV) with the extremely thin film thickness allows for a transparent sensor (transmittance of 83% in the visible spectrum) and this fabrication scheme enables the development of flexible gas sensors.

Pd-doped MoS2 monolayer: A promising candidate for DGA in transformer oil based on DFT method

Density functional theory (DFT) method was carried out to simulate the adsorption of three dissolved gases on Pd-doped MOS2 (Pd-MoS2) monolayer. We initially studied the possible structures of Pd-MoS2 monolayer and found that the Pd dopant preferred to be adsorbed onto the surface by TMo site. The adsorption and desorption performance, along with the sensing principle of Pd-MoS2 towards three typical gases, including H2, CH4 and C2H2, were analyzed. These analysis indicated that Pd-MoS2 could be a satisfied material for C2H2 and H2 sensing at specific condition; while it is unsuitable for detection of CH4 due to the weak interaction and extremely short recovery time. All these give a first insight into the application of Pd-MoS2 for DGA, evaluating the working operation of the transformer through sensitive detection of H2 and C2H2. We are hopeful that this work would support informative knowledge for experimentalists to realize the potential of Pd-MoS2 in the field of electrical engineering in the near future.

An amperometric hydrogen sensor based on Pt nanoparticles supported multi-wall carbon nanotubes

An amperometric H2 gas sensor was fabricated on microporous PTFE sheet using Pt NP-decorated on multiwalled carbon nanotubes (MWNTs) via wet chemical synthesis and vacuum filtration processes. The various material analysis methods such as SEM coupled with EDS, TEM, and XRD were employed in order to characterize microstructures, morphologies and elemental composition of the prepared Pt-MWNTs material. The electrode showed the nanoporous structures with intricate surface morphology as a consequence of Pt agglomerates bonded to MWNTs. The TEM and XRD results confirmed the small Pt nanoparticles (Pt NPs) sizes of 0.5–4.7nm and the polycrystalline face-centered cubic (fcc) structures. The measured electrochemical surface area (ESA) of the Pt-MWNTs-modified glassy carbon electrode was 235.2cm2/mg by using cyclic voltammetry (CV) which was 1.2 times higher than that of commercial 20wt% Pt-C (E-Tek). Furthermore, amperometric gas sensing measurements were performed to evaluate the gas sensing properties of sensor. The Pt-MWNTs electrode shows high sensitivity of 0.269μA/ppm in H2 detection, an excellent linear response, reproducibility and long term stability. Moreover, this electrode was also evaluated in terms of response and recovery times, high detective limit of cross-selectivity to interfering species such as CO, NH3. Therefore, the obtained results show good sensing performance of Pt-MWNTs electrode of H2 detection.

Realization of an H2/CO dual-gas sensor using CoPd magnetic structures

We demonstrated the application of CoPd magnetic devices in single (H2) and dual (H2 and CO) gas detection by varying the thin-film structure. The anomalous Hall effect provided the read-out signal of the devices. The dual-gas sensor was particularly useful for examining whether methane reformation by steam was completed during H2 production where CO is a byproduct. Through in situ Fourier transform infrared and X-ray absorption spectroscopy, we discovered that H2 detection involved a charge-transfer effect between Co and Pd in addition to a surface-adsorption process, for both multilayer and alloy structures; however, CO detection was solely associated with a surface-adsorption process, which only occurred in the alloy structure. The proposed devices demonstrated performances exceeding those of current commercial models (solid-state based) regarding power consumption (<5 mW) because they were not required to undergo a heating process. An Arduino prototype platform was employed to test the modularization of the device, and adequate feasibility was demonstrated.

Nano-bitter gourd like structured CuO for enhanced hydrogen gas sensor application

Hydrogen gas sensing were investigated using nano-bitter gourd like structured CuO material synthesized via a chemical route. Morphology of CuO was revealed using FE-SEM and TEM image analysis. CuO phase confirmation and molecular structural fingerprint were verified by XRD and Raman analysis respectively. Elemental composition and atomic states of elements were investigated by EDS and XPS techniques respectively. A remarkable high gas response of 175% was recorded by CuO sensor towards 100 ppm hydrogen (H2) at the operating temperature 200 °C with response time 150 s. The lowest detection of H2 was observed at 2 ppm concentration with the gas response of 5%. The gas response was studied as functions of different operating temperatures and concentrations. Transient gas response and stability were also confirmed for CuO sensor. Hydrogen sensing mechanism of CuO sensor was elucidated.

High-Temperature Hydrogen Gas Sensor Based on Three-Dimensional Hierarchical-Nanostructured Nickel–Cobalt Oxide

The design of hierarchical metal oxide nanostructured systems has emerged as an effective strategy for improving the performance of hydrogen (H2) gas sensing to facilitate a H2 economy. H2 gas sensors that can operate at elevated temperatures (≥500 °C) are necessary for advanced combustion monitoring and emission control in the automotive industry. Here we report on a hierarchical three-dimensional nickel and cobalt oxide nanomaterial as an efficient high-temperature gas sensor for H2 detection. Our study reveals that the response of the nickel–cobalt oxides strongly depends on the morphology and ratio of Ni/Co. The flower-like NiO nanomaterial demonstrates a p-type response to H2 at 300–500 °C and an n-type response to H2 gas at 600 °C. The developed nickel–cobalt oxide sensor exhibits a unique performance and superior sensitivity at elevated temperatures of ∼500 °C but a negligible response at 300–400 °C. A high surface area with small nanopores and a sensitive change in the crystalline nature at >500 °...

MEMS-based microheaters integrated gas sensors

In the present work efforts have been made to develop microheater integrated gas sensors with low power consumption. The design and simulation of a single-cell microheater is carried out using ANSYS. Low power consumption (<35 mW) platinum micro-heater has been fabricated using bulk micromachining technique on silicon dioxide membrane (1.5 μm thin), which provided improved thermal isolation of the active area of 250 × 250 μm2. The micro-heater has achieved a maximum temperature of ∼950 °C at an applied dc voltage of 2.5 V. Fabricated mircro-heater has been integrated with SnO2 based gas sensors for the efficient detection of H2 and NO2 gases. The developed sensors were found to yield the maximum sensing response of ∼184 and ∼2.1 with low power consumption of 29.18 and 34.53 mW towards the detection of 1 ppm of NO2 gas and 500 ppm of H2 gas, respectively.

Fabrication of ZIF-8 encapsulated ZnO microrods with enhanced sensing properties for H2 detection

As one of the most typical fault characteristic gases in transformer oil, the content of H2 is an important criterion for judging the operation state of power transformers; while online monitoring of such species through gas sensing technology could effectively detect latent faults and avoid accidents. Zinc oxide is a popular sensing material in recent years with limited sensitivity, selectivity and stability for gas detection, while zeolite imidazolate framework-8 (ZIF-8), one kind of metal–organic frameworks (MOFs) materials, possesses adjustable porosity, huge specific surface areas and good thermal stability, so it could perfectly remedy those defects. This paper studied gas-sensing properties of ZnO rods encapsulated by ZIF-8 (ZnO@ZIF-8) for H2. The morphologies, structures, and composition were characterized in detail by means of X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and energy disperse spectroscopy. H2 gas sensing properties of pure ZnO and ZnO@ZIF-8 composites were implemented based on gas sensing platform. Results suggested that the ZnO@ZIF-8 showed better sensitivity, selectivity and stability than pure ZnO rods, and meanwhile possessed lower optimum operating temperature upon H2 detection. Meanwhile the gas-sensing mechanism was analyzed comprehensively from three aspects of sensitivity, selectivity and stability. Our aim of this work is to propose a novel core–shell material with enhanced performance for H2 sensing and provide a new idea for developing high-performance materials to detect fault characteristic gases.

High-Performance Nanowire Hydrogen Sensors by Exploiting the Synergistic Effect of Pd Nanoparticles and Metal-Organic Framework Membranes.

Herein, we report the fabrication of hydrogen gas sensors with enhanced sensitivity and excellent selectivity. The sensor device is based on the strategic combination of ZnO nanowires (NWs) decorated with palladium nanoparticles (Pd NPs) and a molecular sieve metal-organic framework (MOF) nanomembrane (ZIF-8). The Pd NPs permit the sensors to reach maximal signal responses, whereas the ZIF-8 overcoat enables for an excellent selectivity. Three steps were employed for the fabrication: (i) coating of a miniaturized sensor with vapor-grown ZnO NWs, (ii) decoration of these NWs with Pd NPs by atomic layer deposition, and (iii) partial solvothermal conversion of the tuned NWs surface to ZIF-8 nanomembrane. The microstructure and composition investigations of the ZIF-8/Pd/ZnO nanostructured materials confirmed the presence of both metallic Pd NPs and uniform ZIF-8 thin membrane layer. The integration of these nanomaterials within a miniaturized sensor device enabled the assessment of their performance for H2 detection at concentrations as low as 10 ppm in the presence of various gases such as C6H6, C7H8, C2H5OH, and CH3COCH3. Remarkably high-response signals of 3.2, 4.7, and 6.7 ( Ra/ Rg) have been measured for H2 detection at only 10, 30, and 50 ppm, whereas no noticeable response toward other tested gases was detected, thus confirming the excellent H2 selectivity obtained with such a sensor design. The results obtained showed that the performance of gas sensors toward H2 gas can be greatly increased by both the addition of Pd NPs and the use of ZIF-8 coating, acting as a molecular sieve membrane. Furthermore, the presented strategy could be extended toward the sensing of other species by a judicious choice of both the metallic NPs and MOF materials with tuned properties for specific molecule detection, thus opening a new avenue for the preparation of highly selective sensing devices.

Study on simultaneous detection of CO and H2 with (Pd, Fe)-modified SnO2 and Pt-loaded SnO2 sensors

The (Pd, Fe)-modified SnO2 (S1) and Pt-loaded SnO2 (S2) are synthesized via a sol–gel method. As S1 has better selectivity to CO against H2 while S2 to H2 against CO at 400 °C. Thus S1 and S2 can be used to detect the concentration of CO and H2, respectively. However, neither S1 nor S2 can detect the concentration of CO and H2 when they coexist. In this paper, S1 and S2 sensors are used simultaneously for mixed gas of CO and H2 detection, and the respective concentration of CO and H2 is calculated. The calculation process is explained as follows: the response of S1 (R1) and S2 (R2) to a fixed concentration of mixed gas of CO and H2 is obtained in experiment, respectively. So we can calculate the concentration of CO and H2 by using simultaneous equations with the independent variable R1 and R2. Contrast real values with calculated values of CO and H2 concentration, the error margin are all less than 5%, which indicates that this method may be a promising candidate for enhancing the selectivity of semiconductor-based gas sensor to two or more gases.