Selective Detection Of Hydrogen Research Articles

Metal organic framework-derived porous Ni-doped In2O3 for highly sensitive and selective detection to hydrogen at low temperature

Achieving high sensitivity and selective detection at low temperature is of great significance for hydrogen leakage monitoring and early warning. As a very promising hydrogen sensitive material, In2O3 still faces great challenges in achieving high-performance hydrogen sensing at low temperatures due to inherent defects such as low specific surface area and limited active sites. Here, we prepared Ni-doped In2O3 mesoporous nanomaterials using metal organic framework (MOF) as sacrificial templates. The prepared Ni-doped In2O3 exhibited mesoporous structures with small diameters (2–3 nm), which could be used as effective molecular sieves for the selective detection of hydrogen. The high specific surface area (72.0 m²/g) provided numerous active sites for surface redox reactions, resulting in a remarkable hydrogen sensing response. Notably, gas sensitivity tests demonstrated that the Ni-doped In2O3 gas sensor achieved optimal hydrogen detection performance at 100°C. Particularly, the 3 at% Ni-doped In2O3 nanomaterials exhibited a high response of 12.5–100 ppm hydrogen, along with favorable response/recovery time and a practical limit of detection down to 5 ppm. Furthermore, the Ni-doped In2O3 sensor exhibited excellent reversibility, reproducibility, selectivity and long-term stability. In addition, simulation calculations based on molecular dynamics (MD) and density functional theory (DFT) show that molecular sieve effect is the main reason for the enhanced selectivity, and Ni doping induced oxygen vacancy (OV) defects could enhance gas adsorption. This work could provide technical support for leak detection and warning during hydrogen use, storage and transportation in the future.

First principles study of Rh-doped SnO2 for highly sensitive and selective hydrogen detection

Tin dioxide is a low-cost and efficient material with large potential in applications of hydrogen detection. Doping metals in SnO2 is a solution to further improve its electrical performance, however, atomic-scale understanding of detection mechanism of doped SnO2 is very limited. In this work, first principles and molecular dynamics method are applied to investigate adsorption properties and diffusion effects of CH4, CO2, H2, N2 on Rh-doped SnO2. By calculating adsorption energy, adsorption distance, charge density difference, density of states, it is concluded that Rh-SnO2 shows a strong sensing characteristics towards H2, which is consistent with experiment result. After adsorption of H2, the main energy bands of DOS shift to a lower level of energy, and the Fermi level move to higher level of energy. H2 shows a strong chemical adsorption effect on Rh-SnO2, while CH4, CO2 and N2 only present weak physical adsorption on Rh-SnO2. Furthermore, the diffusion of H2 in Rh-SnO2 is easier than those of other gases. Our study provides a fundamental and new perspective for designing highly sensitive hydrogen gas sensor from atomic and electronic level.

Fiber optic localized surface plasmon resonance hydrogen sensor based on gold nanoparticles capped with palladium

We propose an optical fiber-based localized surface plasmon resonance sensor to overcome limitations with hydrogen gas explosions in various types of hydrogen sensors and minimize human damage caused by exposure to hazardous environments. For selective detection of hydrogen, a simple palladium-capping process was applied on a fiber-optic localized surface plasmon resonance. After the palladium-capping, the sensor was exposed to various refractive index solutions to confirm the linearity of the response. Hydrogen gas reactivity was measured at concentrations from 0.8% to 4%; the reaction time at each concentration was observed as 116 s until the signal stabilized. The coefficient of variation (CV) and limit of detection (LOD) were calculated based on the results obtained through repeated measurements. The reproducibility was verified with an average CV of 11%. In addition, the developed sensor showed a low LOD of 0.086%. The hysteresis characteristic was observed within 1% in the output change, which was similar to the fluctuation range allowed by the light source per time. The proposed sensor based on the optical principle is expected to reduce the risk of explosions and has advantages in a simple configuration and low-cost production based on optical fiber.

Highly Sensitive and Selective Detection of Hydrogen Using Pd-Coated SnO2 Nanorod Arrays for Breath-Analyzer Applications.

We report a breath hydrogen analyzer based on Pd-coated SnO2 nanorods (Pd-SnO2 NRs) sensor integrated into a miniaturized gas chromatography (GC) column. The device can measure a wide range of hydrogen (1–100 ppm), within 100 s, using a small volume of human breath (1 mL) without pre-concentration. Especially, the mini-GC integrated with Pd-SnO2 NRs can detect 1 ppm of H2, as a lower detection limit, at a low operating temperature of 152 °C. Furthermore, when the breath hydrogen analyzer was exposed to a mixture of interfering gases, such as carbon dioxide, nitrogen, methane, and acetone, it was found to be capable of selectively detecting only H2. We found that the Pd-SnO2 NRs were superior to other semiconducting metal oxides that lack selectivity in H2 detection. Our study reveals that the Pd-SnO2 NRs integrated into the mini-GC device can be utilized in breath hydrogen analyzers to rapidly and accurately detect hydrogen due to its high selectivity and sensitivity.

Self-Assembled 1-Octadecanethiol Membrane on Pd/ZnO for a Selective Room Temperature Flexible Hydrogen Sensor.

A layer of self-assembled 1-octadecanethiol was used to fabricate a palladium (Pd)/zinc oxide (ZnO) nanoparticle-based flexible hydrogen sensor with enhanced response and high selectivity at room temperature. A palladium film was first deposited using DC sputtering technique and later annealed to form palladium nanoparticles. The formation of uniform, surfactant-free palladium nanoparticles contributed to improved sensor response towards hydrogen gas at room temperature. The obtained sensor response was higher than for previously reported room temperature Pd/ZnO sensors. Furthermore, the use of the polymer membrane suppressed the sensor’s response to methane, moisture, ethanol, and acetone, resulting in the selective detection of hydrogen in the presence of the common interfering species. This study shows a viable low-cost fabrication pathway for highly selective room temperature flexible hydrogen sensors for hydrogen-powered vehicles and other clean energy applications.

Synergistic Acceptor-Donor Interplay of Nd2Sn2O7 Pyrochlore based Sensor in Selective Detection of Hydrogen

Nanostructured thin film of Nd2Sn2O7 pyrochlore obtained by solution processing of a single molecular precursor with Nd-Sn ratio of 1:1 was found to show unprecedently high selectivity towards hydrogen sensing in the temperature range 200 °C–450 °C. Formation of crystalline Nd2Sn2O7 upon annealing the xerogel in air at 800 °C was confirmed by powder X-ray diffraction analysis. The heat-treated pyrochlore films exhibited a porous structure with interconnected grains confirmed by scanning electron microscope images. The gas sensing behavior of the device towards various analyte gases (H2, CO, CH4, NO2, NH3) showed remarkably high selectivity towards H2, while no sensor response against other reducing and oxidizing gases was monitored. The highest sensitivity towards H2 was detected at 300 °C with a linear trend observed in the sensitivity values and H2 concentration (5%–30%). Intercorrelated analysis of sensor characteristics, surface spectroscopy before and after hydrogen treatment and implications of unique crystallographic features of the pyrochlore lattice demonstrated a novel defined subsequent detection mechanism, which strongly differs from conventional binary oxides like SnO2. The significant increase in operating temperature upon H2 exposure is apparently caused by the exothermic reaction between pyrochlore and molecular hydrogen to generate highly reactive hydride species during the detection mechanism. The high efficiency and reproducibility of the investigated sensor devices indicates the potential of Nd2Sn2O7 based sensors for hydrogen safety applications.

Facile synthesis of Al–Mg co-doped ZnO nanoparticles and their high hydrogen sensing performances

Recently hydrogen has received a great attention as a renewable, clean and high-efficiency source of energy. However, its high explosiveness and leakage increased demand for sensors to monitor hydrogen during production, transport, storage and use. This paper presents a new nanostructured material for hydrogen monitoring. Indeed, to our knowledge, the aluminum/magnesium co-doped ZnO nanoparticles are used in the first time for hydrogen sensing. Al(5%)-Mg(1,3,5%) co-doped ZnO nanoparticles were effectively synthesized by facile sol-gel method in supercritical conditions. The structural, morphological and optical properties have been examined by different techniques. X-ray diffraction data confirmed the hexagonal wurtzite structure and showed a good enhancement of crystallinity with introduction of Al and Mg dopants. Transmission electron microscopy observations showed the nanometric size of the nanoparticles (15–25 nm) and the prismatic like shape of the crystallites. The TGA study proves the stability of the samples and the BET analysis illustrate that the isotherm of the 5A1MZO sample is belong to type II. Ultraviolet–Visible spectroscopy measurements evidenced the narrowing of the band gap energy for the co-doped samples which range between 3.14 and 3.19 eV. Photoluminescence spectra of all samples consist of two major components: a narrow ultraviolet emission band and a broad visible emission band (above 500 nm). Electrical properties were also studied. The synthesized samples have been screen printed and investigated as active layer for conductometric gas sensor devices. Their sensing characteristics towards wide range of hydrogen concentrations (100–30,000 ppm) were tested at various temperatures ranging from 200 to 400 °C in dry air. The Al(5%)-Mg(1%) co-doped ZnO sensor displayed the best sensing performances, showing a fast (3 s) and high (larger than 70) response towards 2000 ppm hydrogen at 250 °C. In addition, it showed low detection limit, good repeatability and high selectivity against various interfering gases. Compared to others recent works, the sensor showed competitive performances and by considering the facile, fast and low cost synthesized method of nanoparticles, it represents a promising material for the selective detection of hydrogen.

Selectivity improvement towards hydrogen and oxygen of solid electrolyte sensors by dynamic electrochemical methods

Solid electrolyte sensors (SES) based on yttria-stabilized zirconia (YSZ) can exhibit improved selectivity to redox active gases when they are operated with dynamic electrochemical methods like cyclic voltammetry (CV) or impedance spectroscopy (IS). To clarify basic electrochemical processes at the measuring electrode, experiments in the temperature range 650–750 °C with precise control of hydrogen, oxygen, and water vapor concentrations in non-equilibrated gas mixtures have been conducted. The results show that it is possible to detect hydrogen and oxygen selectively in oxidizing and in reducing gas mixtures with SES operated with CV at different scan rates and polarization ranges.Hydrogen-related peaks appear during anodic scan direction at potentials between -0.4 and -0.2 V vs. Pt/air reference and scan rates between 10 and 100 mV/s. Their heights increase with H2-concentration, temperature, and negative shift of the negative CV limit, providing a lower limit of detection below 5 vol.-ppm and an upper limit of detection at around 100 vol.-ppm at 700 to 750 °C. Oxygen-related peaks arise in cathodic scan direction at potentials between -0.1 and -0.4 V and scan rates between 100 and 1000 mV/s. Their heights also increase with O2-concentration and temperature, providing a lower limit of detection below 5 vol.-ppm and an upper limit of detection above 200 vol.-ppm at 650 °C. Water vapor causes decreasing H2-related peak heights, suggesting an occupation of electrode surface places needed for H2 reaction. In contrast to that, additionally conducted impedance spectroscopy experiments in the frequency range from 0.2 to 105 Hz did not provide further information about the selective detection of hydrogen and oxygen in non-equilibrated gas mixtures.

Temperature dependent selective detection of hydrogen and acetone using Pd doped WO3/reduced graphene oxide nanocomposite

Reduced graphene oxide (RGO) and Pd doped WO3 nanocomposites were fabricated by employing electrostatic interactions between poly (diallyldimethylammonium chloride) (PDDA) modified Pd doped WO3 nanostructures and graphite oxide (GO) and studied for their gas sensing application. XRD, Raman, FTIR, FESEM-EDX, TEM, TGA, XPS and Photoluminescence techniques were used for characterization of as-synthesized samples. Gas sensing studies revealed that the sensor with optimized doping of 1.5 mol% Pd and 1 wt% GO shows temperature dependent selectivity towards hydrogen and acetone. The role of WO3, Pd and RGO has been discussed in detail for enhanced sensing performance.

Bilayer structures based on metal phthalocyanine and palladium layers for selective hydrogen detection

In this work, bilayer structures in which a Pd layer was deposited on the surface of palladium phthalocyanine film (PdPc/Pd) by a Metal-Organic Chemical Vapor Deposition technique were studied as active layers of chemiresistive sensors for selective detection of hydrogen. Surface morphology, microstructure and composition of Pd layers were investigated by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Three sets of bilayer structures with Pd layer thicknesses of 55–80 nm, 100–120 nm and 140–160 nm were obtained to examine the effect of the thickness on the electrical sensor response toward gaseous hydrogen (1–30 v.%). It has been shown that the bilayer structures with 55–80 nm thick Pd layers exhibit the maximal sensor response and can be effectively used for selective detection of hydrogen in the concentration range from 1 to 30% in the presence of gaseous ammonia, CO2, NO2, and chlorinated alkane vapours.

High temperature selective sensing of hydrogen with MgO-modified SrMoO4 micro-fibers

Micro-fibers of Mg-doped SrMoO4 (SrMoO4/MgO) were synthesized using a two-step hydrothermal technique. The SrMoO4/MgO micro-fibers were used as the sensing material within a solid-state, resistive-type sensor architecture. The material showed selective detection of hydrogen (H2) up to 1000°C with high sensor response and stability for the given concentrations. The maximum relative resistance change values (Rmax) for SrMoO4/MgO for 4000ppm H2 in a N2 atmosphere (1% O2) were −31, −85, and −87.5 for 600, 800 and 1000°C, respectively. At 1000°C, and the same background atmosphere, the Rmax was only −2.5 and −12.5 to 4000ppm CO and 2000ppm SO2, respectively. Chemical characterization showed that the Mg was dissolved into the SrMoO4 structure, in addition to residual MgO precipitate found within the final SrMoO4 powder. The surface MgO was shown to affect the H2 adsorption and dissociation processes in addition to high selectivity for H2 in comparison to SO2 and CO, while the dissolved Mg contributed to the alteration of the electronic properties, where the Schottky barrier height, band gap, and work function were all lowered. These combined effects resulted in the favorable sensitivity and high selectivity to H2, and also contributed to the increased stability at the elevated sensing temperatures.

Influence of CuO nanostructures morphology on hydrogen gas sensing performances

In this study, the impact of different morphologies of p-type copper oxide nanostructures on hydrogen gas response is investigated. Sensor structures based on CuO nanowire (NW) networks demonstrated much higher gas response (~340) than nanostructured films (~3) at operating temperatures of 300°C. Such a high gas response in the case of CuO NW networks is explained by percolating phase transition of CuO NW surface to metallic Cu. The phenomenon is observed at operating temperatures higher than 275°C, but show good reversibility at 300°C. At a higher operating temperature of 400°C, the gas response was found lower (~108) than at 300°C, even if the response time and percolating time were much shorter. On the other hand, the faster recovery time (~2s) to the initial value of electrical baseline was observed at an operating temperature of 300°C. This latter temperature is found the best regime for stable and highly sensitive and selective detection of hydrogen with high repeatability for sensor structures based on CuO NW networks. These results will help to take full advantage of these functional nanomaterials in the new generation of sensorial nanodevices for their larger scale utilization.

Tuning H2 Sensing Performance of Zirconia-based Sensor using ZrSiO4(+Au) Sensing-electrode

We are reporting here a potentiometric sensor by using yttria-stabilized zirconia (YSZ) as a solid electrolyte as well as zirconium silicate (ZrSiO4) added with Au as a sensing electrode (SE), for achieving sensitive and selective detection of hydrogen (H2). The addition of 10wt.%Au into ZrSiO4-SE increased the sensitivity toward 100ppm H2 at 500°C, while lower responses to other examined gases were observed. The ability to detect H2 selectively was elucidated via polarization-curve measurements in air and in N2 and confirmed via gas conversion test. It was found that the sensitive and selective H2 behavior was due to a lower catalytic activity against the gas-phase oxidation of H2 than that of C3H6, in combination with a higher catalytic activity to anodic reaction of H2 than that of C3H6. The good agreement between the observed sensitivity and the estimated value from the polarization-curve measurements confirmed that the sensing mechanism is based on mixed potential model. The sensor using ZrSiO4(+ 10wt.%Au)-SE demonstrated a linear relationship between sensitivity and H2 concentration on a logarithmic scale and was capable of detecting H2 concentration as low as 20ppm at 500°C under humid conditions.

N- to p- type carrier reversal in nanocrystalline indium doped ZnO thin film gas sensors

Selectivity has been the central issue in the research area of semiconducting metal oxide gas sensors and still remains a challenge for the researchers. In the present work, we report a promising hydrogen (reducing gas) sensing characteristics of nanocrystalline indium doped zinc oxide thin film sensing elements. At sensor operating temperature in the range (200–300) °C, ‘n’ to ‘p’ type carrier reversal is detected in the measured resistance transients. Furthermore, for a given operating temperature the type of carriers remain unaltered for each concentrations of gas. Thus, temperature plays a crucial role for this transition irrespective of the gas concentration. However, such carrier reversal is not observed in NO2 (oxidizing gas) environment even with the variation of operating temperature and gas concentration. This is attributed to the gas sensing mechanism related to the surface conductivity and the underlying variations of the carrier type. It is argued that, it can pave the way for selective detection of hydrogen at lower operating temperatures.

Strongly coupled hybrid nanostructures for selective hydrogen detection – understanding the role of noble metals in reducing cross-sensitivity

Noble metal-semiconductor hybrid nanostructures can offer outperformance to gas sensors in terms of sensitivity and selectivity. In this work, a catalytically activated (CA) hydrogen sensor is realized based on strongly coupled Pt/Pd-WO3 hybrid nanostructures constructed by a galvanic replacement participated solvothermal procedure. The room-temperature operation and high selectivity distinguish this sensor from the traditional ones. It is capable of detecting dozens of parts per million (ppm) hydrogen in the presence of thousands of ppm methane gas. An insight into the role of noble metals in reducing cross-sensitivity is provided by comparing the sensing properties of this sensor with a traditional thermally activated (TA) one made from the same pristine WO3. Based on both experimental and density functional theory (DFT) calculation results, the cross-sensitivity of the TA sensor is found to have a strong dependence on the highest occupied molecular orbital (HOMO) level of the hydrocarbon molecules. The high selectivity of the CA sensor comes from the reduced impact of gas frontier orbitals on the charge transfer process by the nano-scaled metal-semiconductor (MS) interface. The methodology demonstrated in this work indicates that rational design of MS hybrid nanostructures can be a promising strategy for highly selective gas sensing applications.

Selective Hydrogen Detection in a Highly Contaminated Background Using only a Single Generic Metal Oxide Gas Sensor

Detection of highly ppm range hydrogen concentration in atmospheres contaminated with various volatile organic compounds is in demand for numerous applications. Different devices and techniques have been applied for the problems which are mostly based on utilization of hydrogen permeable membranes. Here, we have used a single generic metal oxide gas sensor for this task. No filter or membrane is utilized. The operating temperature of the sensor is modulated with a voltage waveform specifically designed for producing step-like temperature changes on the oxide pallet. By applying four different step-like temperature jumps, each of 1s duration, the sensor produces response patterns which are processed with common pattern recognition techniques. The technique was examined by its practical use for the ~10 ppm (volume) hydrogen measurement in a background containing ~1000 ppm ethanol. The analysis takes only 4s, and the obtained patterns are reproducible.

Stabilized zirconia-based sensor utilizing SnO2-based sensing electrode with an integrated Cr2O3 catalyst layer for sensitive and selective detection of hydrogen

A highly selective hydrogen (H2) sensor has been successfully developed by using an yttria-stabilized zirconia (YSZ)-based mixed-potential-type sensor utilizing SnO2 (+30 wt.% YSZ) sensing electrode (SE) with an intermediate Al2O3 barrier layer which was coated with a catalyst layer of Cr2O3. The sensor utilizing SnO2 (+30 wt.% YSZ)-SE was found to be capable of detecting H2 and propene (C3H6) sensitively at 550 °C. In order to enhance the selectivity towards H2, a selective C3H6 oxidation catalyst was employed to minimize unwanted responses caused by interfering gases. Among the examined metal oxides, Cr2O3 facilitated the selective oxidation of C3H6. However, the addition or lamination of Cr2O3 to SnO2 (+30 wt.% YSZ)-SE was found to diminish the sensing responses to all examined gases. Therefore, an intermediate layer of Al2O3 was sandwiched between the SE layer and the catalyst layer to prevent the penetration of Cr2O3 particles into the SE layer. The sensor using SnO2 (+30 wt.% YSZ)-SE coated with a catalyst layer of Cr2O3 as well as an intermediate layer of Al2O3 exhibited a sensitive response toward H2, with only minor responses toward other examined gases at 550 °C under humid conditions (21 vol.% O2 and 1.35 vol.% H2O in N2 balance). A linear relationship was observed between sensitivity and H2 concentration in the range of 20–800 ppm on a logarithmic scale. The results of sensing performance evaluation and polarization curve measurements indicate that the sensing mechanism is based on the mixed-potential model.

Selective hydrogen detection at high temperature by using yttria-stabilized zirconia-based sensor with coupled metal-oxide-based sensing electrodes

A selective and sensitive hydrogen (H2) sensor capable of working at a high operating temperature was developed by using a pair of metal-oxide-based SEs formed on a yttria-stabilized zirconia (YSZ) tube, operating as a mixed-potential type sensor. The utilization of SnO2 (+30wt.% YSZ) electrode together with NiO-TiO2 electrode configured as a combined-type sensor, successfully diminished the response of the examined interfering gases (especially propene), while maintaining high response toward H2 at an operating temperature of 600°C under humid operating conditions. The developed sensor exhibited quick response to 100ppm H2, as the 90% response time was observed to be 9s. The sensing performance of the combined-type sensor was barely affected by changes in water vapor concentration within the range of 1–4vol.%, suggesting the resilience of the sensor to function in realistic working conditions. This sensor exhibited a linear relationship between sensitivity and H2 concentration on a logarithmic scale.

Development of Thin Film and Nanorod ZnO-Based LEDs and Sensors

ABSTRACTThe development of new etching and contact metallurgies for the ZnO/ZnMgO/ZnCdO materials system and various approaches for realizing ZnO LEDs are reviewed. ZnO nanorod MOSFETs and pH sensors have been demonstrated. In addition, selective detection of hydrogen with Pt-coated single ZnO nanorods is discussed discussed. The Pt-coated single nanorods show a current response approximately a factor of three larger at room temperature upon exposure to 500ppm H2 in N2 than thin films of ZnO. The power consumption of these sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The ZnO nanorods are insensitive to oxygen in the measurement ambient.

Pt-coated InN nanorods for selective detection of hydrogen at room temperature

Single crystal InN nanorods were successfully grown on c-Al2O3 by hydride-metalorganic vapor phase epitaxy. The measured resistance of bare InN nanorods does not change upon exposure to hydrogen ambient. The addition of sputter-deposited clusters of Pt onto the surface of the InN nanorods, however, produced a significant change in the measured room temperature resistance. The measured resistance changed systematically by 0.5%–12% as the ambient hydrogen concentration in N2 was varied between 10 and 250 ppm after 15 min exposure time. Importantly, a relatively low power consumption of ∼0.3mW was measured under these conditions. There was no response at room temperature to O2, N2O, or NH3 exposures.