High-performance Hydrogen Sensor Research Articles

Pd-based eye-readable H2 sensors: Principles, developments, and perspectives

Hydrogen gas is considered as the ultimate energy carrier to solve the energy crisis, but safely handling hydrogen energy relies on the development of high-performance hydrogen sensors. Compared with widely investigated electric sensors, eye-readable hydrogen sensors (EHSs) have the advantage of higher safety coefficient and lower cost. Therefore, EHSs are more promising to provide basic sensing services for broader application scenarios in daily life, and they have attracted ever-increasing attention recently. However, comprehensive summaries of recent developments in EHSs are rarely reported. In this review paper, three types of Pd-based EHSs with the sensing mechanisms of localized surface plasmon resonance (LSPR), mechanical deformation, and PdO reduction are presented. The development, working principles, sensing performances, and relative merits of each type of EHS are summarized and discussed. This review not only attempts to expound the present strategies for fabricating EHSs, but also aims to inspire the design of more ingenious sensors to pursue higher sensing performance and promote further development in this field. Furthermore, a perspective and some unsolved challenges in EHSs are discussed in the end.

Highly sensitive fiber grating hydrogen sensor based on hydrogen-doped Pt/WO3

Hydrogen sensors are key to the emerging clean hydrogen economies and fiber-optic hydrogen sensors play a unique role owing to their inherent safety and high sensitivity. Currently Pt/WO3 has been employed as the mainstream hydrogen-sensitive material in high performance hydrogen sensors. Here we develop an ultrasensitive fiber-optic hydrogen sensor with fast response by coating pretreated Pt/WO3 nanomaterial on fiber Bragg grating. We observe a great enhancement in sensitivity by the hydrogen-doping of the Pt/WO3 nanomaterials. The generation of HxWO3 composite material is confirmed by XRD, FTIR and Raman analysis. Compared with pure Pt/WO3, a 184-fold improvement in sensitivity is achieved by hydrogen doping, with a fast response of 25 s. An impressive limit of detection (LOD) of 30 ppm is demonstrated by employing both the narrowband weak FBGs and the hydrogen-doped Pt/WO3. The immunity to ambient temperature fluctuation is demonstrated by self-calibration through detecting the wavelength difference between a pair of FBGs. Good specificity is also demonstrated. This technology shows great potential in high spatial-resolution quasi-distributed hydrogen sensing.

Enhanced H2 sensing performance of Pd-modified ZnO nanorods under visible light excitation

High-performance room-temperature hydrogen (H2) sensors are the optimal choice for practical applications. Light excitation, especially visible light, is safer and requires less power compared to ultraviolet (UV) light. This makes it an effective method for achieving room temperature operation. In this study, different mass ratios of Pd-modified ZnO nanorods were synthesized using a combination of hydrothermal and impregnation methods, and their sensing performance to H2 under visible light excitation was investigated. Material characterization results demonstrated that the localized surface plasmon resonance (LSPR) effect of Pd broadened the absorption in the visible light region, increasing the generation of high-energy hot electrons. Notably, the 2.5 wt% Pd/ZnO exhibited excellent sensing performance towards 5000 ppm H2 at room temperature under visible light excitation, with a high response value of 5906.78. The LSPR effect and the catalytic activity of Pd nanoparticles significantly enhance the sensing performance of H2. Based on our current knowledge, there have been no explicit reports on the detection of H2 using visible light excitation with Pd/ZnO, thus highlighting a new direction for the study of room temperature H2 sensors.

Printed, Flexible, Ionic Liquid-Based Hydrogen Sensor via Aerosol Jet Printing of Nanomaterials

Low-cost, high-performance hydrogen sensors are highly demanded in hydrogen leakage detection. To increase the sensitivity and reliability of the hydrogen sensor, an ionic liquid (IL)-based electrochemical gas sensor is fabricated with bimetallic Platinum–Nickel (Pt-Ni) nanoparticles (NPs) with aerosol jet printing technology for continuous monitoring of hydrogen concentration. The Pt-Ni NPs covering the top surface of the metal electrodes can accelerate the catalysis and expand the sensing surface area. When hydrogen gas is sensed at room temperature, the uniquely reversible and rapid redox reactions of hydrogen at the IL/Pt electrode interface, thereby creating continuous measurement capability in a real-time manner with little signal drift. The full coverage of the sensor electrodes will increase the robustness and accuracy of the device. The fabricated sensors demonstrate excellent analytical sensing performance, reaching a limit of detection up to 19.3 ppm. The device takes advantage of an easy fabrication process, simple structure, high sensing response, and low cost, providing a promise for hydrogen sensing at room temperatures.

Ru modulates the catalytic activity of Pt to modify WO3 nanowires for high-performance hydrogen sensing at near room temperature

Hydrogen is the cleanest fuel, but the safe storage and transportation of hydrogen is a relatively troublesome task, thus, developing high-performance hydrogen sensors has certain challenges. In this paper, high-performance hydrogen sensing material at near-ambient temperatures was prepared by using platinum and ruthenium co-modified the surface of WO3 nanowires obtained via electrospinning. When the atomic percentages of platinum (Pt) & ruthenium (Ru) to tungsten (W) is 7:4, the response value of sensors to 1 ppm hydrogen at near room temperature (70 °C) is 1010, making it suitable for practical application. Particularly, the sensor has a low detection limit of 252 ppt, good repeatability, selectivity and long-term stability. In addition, the electrocatalytic dehydrogenation (HER) performance of the samples was investigated and combined with the Raman study to explore the hydrogen sensing mechanism in this work. This work demonstrated that the modification of double noble metals could significantly improve the hydrogen sensing performance of WO3 nanowires, and it is expected to be extended to the practical application of metal oxide semiconductors based chemiresistive hydrogen sensors, which is of great significance for the large-scale safe use of hydrogen energy in the future.

Ultrasensitive hydrogen detection by electrostatically formed silicon nanowire decorated by palladium nanoparticles

Developing high performance hydrogen (H2) sensors is of utmost importance to facilitate the safe usage of H2 as the alternative source of clean and renewable energy. We present an ultra-sensitive H2 sensor operating in air and based on electrostatically formed nanowire (EFN) sensor decorated by palladium nanoparticles (Pd NPs). By appropriate tuning of the various gate voltages of the EFN, an extremely high sensor response of ∼2 × 106 % (0.8 % H2 exposure) and a sensitivity of ∼400 % ppm−1 is obtained at room temperature (20 ± 2 °C). This sensor outperforms, to the best of our knowledge, most of the reported resistive and field effect transistor (FET) based H2 sensors. The EFN power consumption varies from few pW to ∼436 nW at maximum current operation thus enabling ultra-low power usage at room temperature. In addition, the sensor exhibits fast response and recovery times, retains good sensing performances even at 50 % relative humidity (RH) and exhibits reproducibility over time. Combining Pd NPs with the unique features of the EFN platform makes Pd-EFN a versatile, robust, low power, rapid, and highly sensitive H2 sensor.

Fe-doped MoO3 nanoribbons for high-performance hydrogen sensor at room temperature

A series of novel ribbon-like Fe-doped orthorhombic MoO3 (α-MoO3) nanoribbons was synthesized using a facile hydrothermal method. The results showed that the size of the prepared α-MoO3 nanoribbons was inversely related to the concentration of the Fe dopant. The hydrogen sensing performance of the modified nanoribbons improved after increasing the content of the Fe dopant from 2 at% to 6 at% but deteriorated at higher concentrations. The α-MoO3 doped with 6 at% Fe exhibited promising gas sensing performance to 500 ppm H2 at room temperature, with a high sensor response of 19.7 s and a short response time of 21.4 s. The sensor based on Fe-doped α-MoO3 nanoribbons was sensitive to 10–1500 ppm H2 and showed outstanding repeatability, response stability, and selectivity to H2. The experimental results and first-principles DFT calculations indicated that the high specific surface area and Fe dopant atoms were the main factors responsible for the promising hydrogen sensing performance of the modified MoO3. Our study indicates that Fe-doped α-MoO3 nanoribbons can be applied as a gas sensor with excellent hydrogen gas sensing properties at room temperature.

Machine learning-enabled textile-based graphene gas sensing with energy harvesting-assisted IoT application

Flexible gas sensing is attracting more attention with the development of machine learning and Internet of Things (IoT). Herein, we report flexible and foldable high-performance hydrogen (H2) sensor on all textiles substrate-fabricated by inkjet–printing of reduced graphene oxide (rGO) and its application to wearable environmental sensing. The inkjet-printing process provides the advantages of the compatibility with various substrates, the capability of non-contact patterning and cost-effectiveness. The sensing mechanism is based on the catalytic effect of palladium (Pd) nanoparticles (NPs) on the wide bandgap rGO, which allows facile adsorption and desorption of the nonpolar H2 molecules. The graphene textile gas sensor (GT-GS) demonstrates about six times higher sensing response than the graphene polyimide membrane gas sensor due to the large surface area of the textile substrate. An analysis of the temperature influence on the GT-GS shows better H2 gas response at room temperature than at high temperature (e.g., 120 °C). In addition, with the machine learning-enabled technology and triboelectric-textile to power IoT (temperature and humidity for gas calibration), H2 is well identified for wearable applications with a robust mechanical performance (e.g., flexibility and foldability).

Nanoporous Silicon Thin Film-Based Hydrogen Sensor Using Metal-Assisted Chemical Etching with Annealed Palladium Nanoparticles.

This article reports a nanoporous silicon (Si) thin-film-based high-performance and low-power hydrogen (H2) sensor fabricated by metal-assisted chemical etching (MaCE). The nanoporous Si thin film treated with Pd-based MaCE showed improvement over a flat Si thin film sensor in H2 response (ΔI/I0 = 4.36% → 12.4% for 0.1% H2). Furthermore, it was verified that the combination of thermal annealing of Pd and subsequent MaCE on the Si thin film synergistically enhances the H2 sensitivity of the sensor by 65 times as compared to the flat Si thin film sensor (ΔI/I0 = 4.36% → 285% for 0.1% H2). This sensor also showed a very low operating power of 1.62 μW. After the thermal treatment, densely packed Pd nanoparticles agglomerate due to dewetting, which results in a higher surface-to-volume ratio by well-defined etched holes, leading to an increase in sensor response.

Pd-Decorated PdO Hollow Shells: A H2-Sensing System in Which Catalyst Nanoparticle and Semiconductor Support are Interconvertible.

Developing a simple strategy to fabricate high-performance hydrogen sensors with long-term stability remains quite challenging. Here, we report the H2-sensing performance of Pd-decorated PdO hollow shells (Pd/PdO HSs). In this novel system, the catalyst nanoparticles (Pd NPs) and semiconductor support (PdO) are interconvertible, which is different from traditional hydrogen-sensing systems such as Pd/TiO2 and Pd/ZnO. This Pd/PdO system exhibits multiple unique properties. First, well-distributed Pd NPs with controllable density can be decorated on PdO support through a one-step NaBH4 treatment during which PdO is partially reduced into Pd. Second, the decorated Pd NPs are physically inlaid in the PdO support, which not only prevents the agglomeration or detachment of Pd NPs but also enhances the electron transfer between Pd NPs and PdO. Third, Pd/PdO HSs can be reoxidized into PdO HSs once their sensing performance degrades, which repeatedly manipulates Pd/PdO HSs under the initial reduction process, leading to the reactivation of the sensing performance. With all these advantages, Pd/PdO HSs demonstrate a detection limit lower than 1 ppm, a response/recovery time to 1% H2 of 5 s/32 s at room temperature, and a repeatable reactivation ability. The strategy presented here is convenient and time saving and has no need to prefunctionalize the PdO surface for the decoration of catalyst NPs. Moreover, the unique reactivation ability of Pd/PdO system opens a new strategy toward extending the lifetime of H2 sensors.

Reduction of Wind Disturbance by Optimizing the Drive Current of Pt Ultra-thin Film Hydrogen Sensor

Hydrogen gas poses risks of gas leakage and explosion because the size of hydrogen molecule is very small, and its wide range of inflammability (4-75% in air). Therefore, a high-performance hydrogen sensor is indispensable for the widespread safe use of hydrogen energy. In this study, environmental resistance is improved by optimizing the current drive method of Pt ultra-thin film hydrogen sensor. The sensor output was stable even if the gas flow around the sensor changed by driving at the low current (1 mA). In addition, the sensitivity was sufficient under low current drive.

Hydrogen sensors based on Pt-decorated SnO2 nanorods with fast and sensitive room-temperature sensing performance

Hydrogen energy has been regarded as one of the most promising green and renewable energy in future society. The development and application of fast and cost-effective hydrogen sensors are of great significant for the safe application of hydrogen energy. In this work, high-performance semiconductor hydrogen sensors with fast room-temperature (RT) hydrogen response were fabricated by using Pt-decorated SnO2 nanorods. The SnO2 nanorods with tetragonal phase were synthesized through a hydrothermal method, and then decorated by Pt nanoparticles by a photochemical reduction method under UV irradiation. The hydrogen sensing performance of the SnO2 nanorods at RT were greatly enhanced after the Pt-decoration. The sensor response was gradually increased from 27.10% to 87.35% with Pt/Sn mol ratio increasing from 0 to 3.63%. Meanwhile, the response and recovery process were also accelerated with increasing Pt loading amount. The room-temperature response and recovery time of the sensor with Pt/Sn ratio of 3.63% was down to 0.33 and 29.60 s, respectively. The sensor also exhibited outstanding repeatability and selectivity against CO and CH4. Moreover, the impact of humidity on the sensor performance were also investigated. The sensor response was decreased with increasing environmental humidity, which could be partially recovered after the humidity was decreased. The remarkably accelerated sensor performance could be attributed to the catalytic property of Pt nanoparticles with spillover effect and the contribution of Pt-induced metal-semiconductor contact effect to the hydrogen response of the sensors.

High-Performance, Room Temperature Hydrogen Sensing With a Cu-BTC/Polyaniline Nanocomposite Film on a Quartz Crystal Microbalance

In this paper, we demonstrate a high-performance hydrogen sensor under ambient conditions by growing a Cu-BTC/polyaniline (PANI) nanocomposite film on a quartz crystal microbalance (QCM) using intense pulsed light. The QCM was first sputter coated with a 200-nm-thin layer of copper. The copper layer was then oxidized by sodium hydroxide and ammonium persulfate. A solution containing the organic ligand (BTC) and PANI was then dropped and dried on the copper hydroxide surface of a QCM with intense pulsed light which resulted in Cu-BTC/PANI nanocomposite film on a QCM. The gas sensing performance of the Cu-BTC film and Cu-BTC/PANI composite film was compared under ambient conditions. It was found selectivity and sensitivity of the Cu-BTC/PANI nanocomposite film to hydrogen were significantly improved. In addition, a fast response time (from 2 to 5 s), operation at room temperature even in the presence of high relative humidity (up to 60%), good repeatability were achieved with the Cu-BTC/PANI nanocomposite film-grown QCM sensor.

A high-performance hydrogen sensor based on a reverse-biased MoS2/GaN heterojunction

We report a MoS2/GaN heterojunction-based gas sensor by depositing MoS2 over a GaN substrate via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The microscopic and spectroscopic measurements expose the presence of highly crystalline and homogenous few atomic layer MoS2 on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS2/GaN interface under the reverse biased condition, thus resulting in high sensitivity. Our results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature (25–150 °C). For a deeper understanding of carrier dynamics at the heterointerface, we visualized the band alignment across the MoS2/GaN heterojunction having valence band and conduction band offset values of 1.75 and 0.28 eV. The sensing mechanism was demonstrated based on an energy band diagram at the MoS2/GaN interface in the presence and absence of hydrogen exposure. The proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes.

Half-Pipe Palladium Nanotube-Based Hydrogen Sensor Using a Suspended Nanofiber Scaffold.

A half-pipe palladium nanotube network (H-PdNTN) structure was developed for high-performance hydrogen (H2) sensor applications. To fabricate the sensor, suspended poly(vinyl alcohol) (PVA) nanofiber bundles were electrospun on a conductive substrate, followed by a palladium (Pd) deposition on top of the PVA nanofiber bundles. Then, Pd-deposited PVA nanofibers were transferred to a host substrate, and the PVA nanofiber templates were selectively removed. Various material analyses confirmed that the PVA nanofibers were successfully dissolved leaving a half-pipe-shaped Pd nanotube network. The fabricated Pd nanotube-based sensors were tested for H2 responses with different gas concentrations. The 4 nm thick sensor showed the highest response (Δ R/ R0) to H2 gas. Platinum (Pt) decoration of the sensor showed an improved response speed compared to that of the pristine sensor via the catalytic function of Pt. Additionally, the sensor exhibited good H2 selectivity against other interfering gases. The H-PdNTN H2 sensor provides a facile and cost-effective way to fabricate high-performance H2 sensors.

Enhanced Hydrogen Detection in ppb-Level by Electrospun SnO₂-Loaded ZnO Nanofibers.

High-performance hydrogen sensors are important in many industries to effectively address safety concerns related to the production, delivering, storage and use of H2 gas. Herein, we present a highly sensitive hydrogen gas sensor based on SnO2-loaded ZnO nanofibers (NFs). The xSnO2-loaded (x = 0.05, 0.1 and 0.15) ZnO NFs were fabricated using an electrospinning technique followed by calcination at high temperature. Microscopic analyses demonstrated the formation of NFs with expected morphology and chemical composition. Hydrogen sensing studies were performed at various temperatures and the optimal working temperature was selected as 300 °C. The optimal gas sensor (0.1 SnO2 loaded ZnO NFs) not only showed a high response to 50 ppb hydrogen gas, but also showed an excellent selectivity to hydrogen gas. The excellent performance of the gas sensor to hydrogen gas was mainly related to the formation of SnO2-ZnO heterojunctions and the metallization effect of ZnO.

High performance hydrogen sensor based on Pd/TiO2 composite film

Hydrogen sensors with fast response and recovery rate based on nanoporous palladium (Pd) and titanium dioxide (TiO2) composite films supported by anodic aluminum oxide (AAO) template have been demonstrated. Nanoporous TiO2 film was sprayed on the porous AAO templates, followed by Pd film deposited on TiO2 layer by DC magnetron sputtering. We have researched the detection performance of the hydrogen sensors depending on different thickness of TiO2 layer from 6 to 30 nm with keeping the thickness of Pd as 30 nm. The results have demonstrated the sensors with 10 nm thickness of TiO2 achieve the best performance with a response/recovery time as short as 4/8s at 0.8% and 0.4% hydrogen concentration, respectively. The sensors exhibited very good performance under hydrogen concentrations from 0.4% to 1.8%.

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.

A novel approach to fabricating a ternary rGO/ZnO/Pt system for high-performance hydrogen sensor at low operating temperatures

A novel method for the synthesis of a ternary platinum loaded reduced graphene oxide (rGO)/ zinc oxide (ZnO) hybrid nanocomposite via a pulsed laser ablation in liquid (PLAL) and direct current (DC) sputtering for a hydrogen sensing application is reported here. The said composite was fabricated to obtain small ZnO nanoparticles with interfacial electric contact without using chemical reagents. Firstly, ZnO nanoparticles were fabricated by the decomposition of zinc peroxide (ZnO2) quantum dots, synthesized by laser ablation of microstructured Zn powder in 3%H2O2, whereas GO was prepared by the modified Hummer method. Secondly, an rGO/ZnO nanocomposite was prepared via PLAL of ZnO and graphene oxide (GO) in deionized water. Finally, DC sputtering was used to decorate the surface of the rGO/ZnO hybrid with a Pt thin film to obtain a ternary rGO/ZnO/Pt hybrid nanocomposite. Maximum sensing performance was achieved by tuning the thickness of the deposited Pt layer. According to our study, the Pt-loaded rGO/ZnO gas sensor, with a thickness of 2 nm, showed an excellent response and selectivity towards a low concentration of hydrogen, giving a high response of about 99% (−400 ppm), which was 10 and 5 times higher than those of the pure ZnO, and the rGO/ZnO nanocomposite, respectively. This significantly improved response was mainly attributed to the high surface area of the rGO, the fast spill-over effect of the uniformly coated Pt nanoparticles, and the formation of a p-n junction between rGO and ZnO nanoparticles. This study indicates that the obtained rGO/ZnO/Pt hybrid nanocomposite is a promising candidate for constructing high-performance H2 gas sensors.

High-Sensitivity and Low-Power Flexible Schottky Hydrogen Sensor Based on Silicon Nanomembrane.

High-performance and low-power flexible Schottky diode-based hydrogen sensor was developed. The sensor was fabricated by releasing Si nanomembrane (SiNM) and transferring onto a plastic substrate. After the transfer, palladium (Pd) and aluminum (Al) were selectively deposited as a sensing material and an electrode, respectively. The top-down fabrication process of flexible Pd/SiNM diode H2 sensor is facile compared to other existing bottom-up fabricated flexible gas sensors while showing excellent H2 sensitivity (Δ I/ I0 > 700-0.5% H2 concentrations) and fast response time (τ10-90 = 22 s) at room temperature. In addition, selectivity, humidity, and mechanical tests verify that the sensor has excellent reliability and robustness under various environments. The operating power consumption of the sensor is only in the nanowatt range, which indicates its potential applications in low-power portable and wearable electronics.