Sensitive Hydrogen Gas Sensor Research Articles

Highly sensitive and selective hydrogen gas sensor using sputtered grown Pd decorated MnO2 nanowalls

Two-dimensional (2D) materials have attracted significant attention for device applications due to their unique structural, electronic and catalytic properties. Here, we have deposited a vertically aligned, highly ordered Pd decorated MnO2 nanowalls directly on a porous anodic alumina (AAO) by reactive sputtering and then it used as a gas sensor without additional processing. The nanowalls sensor shows remarkably high and selective responses to hydrogen gas with low detection range 10–10000ppm. Our results demonstrate the potential application of Pd decorated MnO2 nanowalls for fabricating highly sensitive and selective gas sensors.

Highly Sensitive Hydrogen Gas Sensors Based on Gold Nanoparticle Decorated Zinc Oxide Nanosheets

Highly sensitive gold nanoparticle decorated zinc oxide nanosheet gas sensors have been fabricated using simple and rapid chemical methods capable of producing a normalised current gain of 2.54 (at 10V) in dry air containing 2.5ppm of hydrogen gas at 200C and a current gain of 382.53 under 125ppm. Compared to undecorated sheet based sensors where a response of 1.24 was observed under 125ppm at 200C a massive relative increase in signal is observed. The zinc oxide nanosheets are produced via a previously reported simple microwave assisted hydrothermal growth method and gold nanoparticles with mean diameter of 5nm synthesized via a simple sodium borohydride reduction of hydrogen tetrachloroaurate in the presence of polyvinylpyrrolidone (PVP) followed by drop casting onto a pre-patterned aluminium oxide substrate.

Hydrogen Sensing Properties of Copper-Doped Zinc Oxide Thin Films

A highly sensitive hydrogen gas sensor has been developed utilizing 3% copper-doped zinc oxide thin films. These films were deposited using pulsed laser deposition technique on quartz substrates with predeposited interdigitated platinum electrodes. The deposited films were characterized by X-ray diffraction and atomic force microscopy. The hydrogen sensing properties of the sensor were studied at three operating temperatures, viz., 50 °C, 100 °C, and 150 °C. We observed that the sensor shows good performance even at a low operating temperature of 50 °C for a very small concentration of hydrogen (10 ppm).

Highly sensitive dual-FET hydrogen gas sensors with a surface modified gate electrode

Low-power dual-FET type H2 sensors were fabricated, and surface modification techniques were developed to control the morphology of the catalytic metal gate. The differential outputs between the sensing FET and the reference FET were preserved even under a thermal change (from 50 °C to 150 °C) due to the same dependence of the electrical characteristics. The proposed sensor design showed low power consumption (45.5 mW 150 °C) by complete heat isolation. The sensors gave stable responses to H2 gas over a wide temperature range, and the temperature of optimal response in micro-heater operation was approximately 150 °C. The surface of the catalytic metal gate was modified with solution based methods using a poly-styrene (PS) nano-beads suspension. The maximum drain current changes of the FET sensors with a nano-bumpy Pd film and a flat-surface Pd film were 164.6 μA and 128.2 μA to 5000 ppm hydrogen, respectively. The gas sensing characteristics of the FET sensor with the nano-bumpy Pd film were much higher than those of the FET sensor with the thin film due to the nano-porosity of the catalytic metal film.

Highly sensitive hydrogen gas sensor based on a suspended palladium/carbon nanowire fabricated via batch microfabrication processes

We present a highly sensitive H2 sensor based on a single Pd-functionalized carbon nanowire suspended ∼10μm above a substrate while monolithically bridging two carbon posts. The carbon nanowire and posts were fabricated using a batch carbon-microelectromechanical system (MEMS) process consisting of photolithography and pyrolysis. The pyrolysis process resulted in a significant volume reduction in which the nanowire diameter was reduced to ∼120nm from the original 1μm×1.5μm photoresist wire. Because of SiO2 eaves formed by isotropic etching of the Si substrate, as well as the suspended geometry of the carbon nanowire, a single palladium evaporation process enabled selective palladium coating on the carbon nanowire without any nano-patterning processes. The electrical conductivity of the carbon nanowire was modulated by varying the pyrolysis temperature so that the electrical resistance along the suspended Pd/C nanowire was affected predominantly by hydrogen chemisorption onto the thin Pd layer enclosing the carbon core. The suspended functionalized wire showed better sensing capability compared to a Pd nanowire fabricated on the substrate with similar dimensions, because of enhanced mass transport. The suspended nanowire-based H2 sensor quantified from 10 to 500ppm H2 with percentile resistance changes of 5.9–129%.

Catalyst-type-an optical fiber sensor for hydrogen leakage based on fiber Bragg gratings

A highly sensitive hydrogen gas sensor based on a fiber Bragg grating (FBG) has been developed. Various potential hydrogen sensor materials were screened by assessing the catalytic activities of oxide-supported platinum particles prepared by a sol–gel method. It was determined that a Pt/SiO2 film was the most appropriate sensor material; exposure of this film to 4vol% H2 in humid air for 30s at room temperature produced a temperature change of 65K. In addition, the Pt/SiO2 was able to respond to a concentration as low as 0.1vol% H2 in dry air. Two types of sensor structures were fabricated and evaluated. The device incorporating a quartz glass substrate covered with the sensor film on one side was able to detect 0.4vol% H2 in dry air at room temperature with a response time of approximately 25min. The other device, in which the sensor film was immobilized on the periphery of the FBG section, exhibited rapid response to 0.6vol% H2 within 20s.

Trace level detection of hydrogen gas using birnessite-type manganese oxide

A new, highly sensitive and selective hydrogen gas (H2) sensor based on birnessite-type manganese oxide (δ-MnO2) nanoflakes was prepared. The δ-MnO2 nanoflakes sensor selectively detected H2 with detection limits in air of 150ppb at 200°C and 7.5ppm at room temperature. In addition, the sensor also exhibited a considerable response to H2 in an N2 atmosphere. The sensor rapidly responded to trace levels of H2 gas and displayed reversible recovery, while the detected H2 concentrations could be accurately calculated using a modified Langmuir isotherm adsorption equation. The influence of the temperature and humidity on the sensing performance of the sensor was also investigated. The mechanism of the sensor is based on the oxidation of H2O and H2 accompanied by the formation and oxidation of MnOOH. It is believed that the low detection limit, high selectivity and fast reversible response of the δ-MnO2 nanoflake sensor are important benefits that make this sensor a promising candidate for H2 leak detection.

Hydrogen sensor using the Pd film supported on anodic aluminum oxide

Highly sensitive hydrogen gas sensors were fabricated using a microelectromechanical system (MEMS) and anodic aluminum oxides (AAOs) process. MEMS based gas sensor platform was designed with the multi-layer type for Pd film morphology manipulations. The operating temperature of the micro heater was positively correlated with the heater. Hydrogen sensing response of the sensor showed a good positive linearity as the gas sensitivity increased with increasing hydrogen concentration. The hydrogen sensitivity (defined as ratio of sensor resistances in air and after the hydrogen gas injection) was 0.638% at hydrogen concentration of 2000 ppm. The H2 sensitivity was very dependent on the thickness and morphology of Pd-nanosized film. The gas sensitivity and response properties showed different behaviors when palladium film was deposited on the anodic aluminum oxide (AAO) layer. The hydrogen sensitivity for the Pd on AAO layer was about 0.783% at the hydrogen concentration of 2000 ppm. The sensitivity of the Pd-AAO layer improved with respect to the pure Pd thin film due to nanoporous nature of AAO.

Asymmetric electron hole distribution in single-layer graphene for use in hydrogen gas detection

We demonstrate a highly sensitive hydrogen gas sensor using single-layer graphene exfoliated from highly oriented pyrolytic graphite, which one side of it was covered by palladium. In this asymmetric graphene sensor, the electrons generated from reaction between palladium and hydrogen accumulate at the interface between palladium and graphene, and these accumulated electrons changed the carrier density of graphene beneath the palladium film from hole-dominated to neutralized graphene. This half-neutralized and half hole-dominant graphene showed asymmetrical I–V characteristics in a hydrogen atmosphere. Moreover, this device showed promising sensing performance in hydrogen gas including good sensitivity, a few second response time, and a few minute recovery time from 50 to 20,000ppm hydrogen depending on the current direction. The fact that the response of the sensor satisfies Sievert’s law, suggests that graphene with lithographically patterned palladium on one half can exhibit direction dependent asymmetrical electric current performance in a hydrogen atmosphere and also can act as a highly sensitive sensor for the quantitative detection of hydrogen molecules over broad concentration ranges.

Vertical ZnO nanorod array as an effective hydrogen gas sensor

We report a vertical ZnO nanorod array as a highly sensitive hydrogen gas sensor. The vertical ZnO nanorod array on an Nb/Si substrate was fabricated using an anodized aluminum oxide nanotemplate and an atomic layer deposition method. The vertical ZnO nanorod array hydrogen gas sensor exhibited a high sensitivity for hydrogen in a wide concentration range.

Design and fabrication of micro hydrogen gas sensors using palladium thin film

A highly sensitive hydrogen gas sensor of the multi-layer, micro heater type was designed and fabricated using a microelectromechanical system (MEMS) process. A sensing layer (Pd thin film) was fabricated by radio frequency (R.F.) magnetron sputtering. The electrothermal properties of the designed H2 sensor were analyzed by the finite elements method (FEM). When the heater voltage was 3.0, 3.5 and 4.0, the simulation data were 98.56, 124.46 and 154.34°C and the measured data were 101.28, 124.20 and 149.42°C, respectively. In both data, the operating temperature of the micro heater was positively correlated with the heater voltage. The results of sensitivity and response time after application of the heater voltage demonstrated an optimal heater voltage for this sensor of 4.0V. The H2 sensor provided sensitivity (Rs) of 0.267% for 500ppm – hydrogen gas at a heater voltage of 4.0V. The gas sensitivity was positively correlated with the hydrogen concentration.

Ultra Sensitive Fiber-Optic Hydrogen Sensor Based on High Order Cladding Mode

We demonstrate a simple but sensitive hydrogen gas sensor composed of a palladium-coated long-period fiber grating (LPG). By writing an LPG in a low core index fiber, high-order cladding modes are excited. As the palladium thin layer absorbs hydrogen, the effective refractive indexes of the cladding modes are affected, thus the resonant wavelengths of the LPG are changed with a high sensitivity. With 70-nm-thick coating, 7.5 nm of the hydrogen-induced spectral shift was achieved. The spectral response of the proposed sensor to hydrogen gas and its recovery with nitrogen gas are presented.

Highly sensitive hydrogen gas sensors using single-walled carbon nanotubes grafted with Pd nanoparticles

We have investigated the hydrogen gas sensing performance of single-walled carbon nanotubes (SWCNTs) grafted with Pd nanoparticles (NPs). The SWCNTs, modified with dendrimers before grafting, were found to have a much faster response time (3 s) and better recovery but lower response (8.6%) at 10,000 ppm hydrogen gas than those prepared without the dendrimer template (253 s, 25%). This can be ascribed to the dipole moments induced by the dendrimers. Removal of the dendrimers by heat treatment resulted in high response (25%), a fast response time (7 s) at 10,000 ppm hydrogen gas, and an ultra-low concentration H 2 detection of 10 ppm at room temperature. In addition, this sample was found to satisfy Sievert's law. Our results demonstrate that SWCNTs grafted with Pd-NPs through a dendrimer-mediated process can be used to fabricate highly sensitive hydrogen gas sensors that exhibit a broad dynamic detection range, fast response times, and excellent recovery.

Structure of palladium nanoclusters for hydrogen gas sensors

Palladium nanoclusters produced by inert gas aggregation/magnetron sputtering are used as building blocks for the construction of nano electronic devices with large surface to volume ratios that can be used as sensitive hydrogen gas sensors in fuel cells and in petrochemical plants. X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), and high resolution transmission electron microscopy (HRTEM) have been used to characterise the structure, lattice constant, particle diameter and oxide thickness of the palladium nanoclusters in order to understand the operation of these sensors. Grazing incidence XRD (GIXRD) of heat treated Pd clusters has shown that the palladanite structure forms at elevated temperatures.

Structure of palladium nanoclusters for hydrogen gas sensors

Palladium nanoclusters produced in an inert gas aggregation/magnetron sputtering source are being used as building blocks for the construction of nano electronic devices with large surface to volume ratios that can be used as sensitive hydrogen gas sensors in fuel cells and in petrochemical plants. Grazing incidence X-ray diffraction (GIXRD) at the Stanford Synchrotron Radiation Laboratory (SSRL) and high resolution transmission electron microscopy (HRTEM) have been used to characterise the structure, lattice constant, particle diameter and oxide thickness of the palladium nanoclusters in order to understand the operation of these sensors.

Room-Temperature Hydrogen Sensing Properties of SnO2 Thin Films Fabricated by the Photochemical Deposition and Doping Methods

SnO2 thin films were fabricated by photochemical deposition (PCD) method for application as a hydrogen gas sensor. The aqueous growth solution contained 10 mmol/L SnSO4, and the pH was adjusted to 2 by addition of HNO3. The growth solution was dropped onto the glass substrate and irradiated using an ultrahigh-pressure mercury arc lamp. To enhance the sensitivity to hydrogen, Pd was doped by a novel photochemical doping method, in which PdCl2 solution was dropped onto the film and irradiated. The photo-Pd-doped films showed an increase in current of about five orders of magnitude at room temperature in 0.5% hydrogen ambient compared with in vacuum. Thus, photo-Pd-doped PCD-SnO2 films operate as a highly sensitive room-temperature hydrogen gas sensor.

Micro-bead of nano-crystalline F-doped SnO 2 as a sensitive hydrogen gas sensor

Gas sensor system was designed and fabricated using micro-electro mechanical system (MEMS) technology, coating the nano-crystalline F-doped SnO 2-based material as a micro-bead on a silicon substrate with Pt electrode and heater by screen-printing method. Gas sensing properties of the sensor were tested against combustible gases like H 2, CO, CH 4, C 3H 8. Nano-crystalline F-doped SnO 2 micro-sensor showed maximum sensitivity for hydrogen gas and little sensitivities for other gases at a heater voltage of 0.7 V. The present micro-sensor showed higher sensitivity and better stability for hydrogen gas in comparison to commercially available SnO 2, and is a low energy consuming portable sensor module that can be mass-produced with nano-crystalline gas sensing material using MEMS technology.

Improved Response Time of Al–Al2O3–Pd Tunnel Diode Hydrogen Gas Sensor

An Al–Al2O3–Pd tunnel diode acts as a sensitive hydrogen gas sensor. A serious drawback, however, of this hydrogen gas sensor operating at room temperature was a very long response time, typically 30 min. To overcome this disadvantage, the Pd tunnel diode was operated at elevated temperatures, resulting in a marked reduction of the response time, less than 1 min at 83°C. A microheater attached to the back surface of the substrate could be an efficient power source to heat the hydrogen sensor to the required temperature.

A highly sensitive and selective hydrogen gas sensor from thick oriented films of MoS2

A new process is developed to fabricate a highly sensitive and selective hydrogen sensor by depositing a partially crystalline and highly oriented film of MoS2 from its single layer suspension on an alumina substrate. When these films are promoted with some catalysts selected from Pt-group metals (Pt, Pd, Ru or any combination of these metals) they exhibit a high sensitivity and selectivity to hydrogen gas. Unlike other metal oxide sensors which are sensitive to many reducing and oxidizing gases and operate at a temperature of 350 °C or higher; this sensor is highly selective to hydrogen gas and its operating temperature is from 25 to 150°C. The lower operating temperature enhances safety when dealing with hydrogen gas. The sensor response to hydrogen at 120 °C is linear in concentration from 30 to 104 ppm with a 10 to 30 second response time and a 45 to 90 second recovery time. Above 104 ppm the sensor is still linear but the slope of conductance versus hydrogen concentration changes.

A highly sensitive and selective hydrogen gas sensor from thick oriented films of MoS 2

A highly sensitive and selective hydrogen gas sensor from thick oriented films of MoS 2