H2 Sensor Research Articles

Hydrogen online monitoring based on thermal conductivity for anaerobic microorganisms.

H2 -producing microorganisms are a promising source of sustainable biohydrogen. However, most H2 -producing microorganisms are anaerobes, which are difficult to cultivate and characterize. While several methods for measuring H2 exist, common H2 sensors often require oxygen, making them unsuitable for anaerobic processes. Other sensors can often not be operated at high gas humidity. Thus, we applied thermal conductivity(TC) sensors and developed a parallelized, online H2 monitoring for time-efficient characterization of H2 production by anaerobes. Since TC sensors are nonspecific for H2 , the cross-sensitivity of the sensors was evaluated regarding temperature, gas humidity, and CO2 concentrations. The systems' measurement range was validated with two anaerobes: a high H2 -producer (Clostridium pasteurianum) and a low H2 -producer (Phocaeicola vulgatus). Online monitoring of H2 production in shake flask cultivations was demonstrated, and H2 transfer rates were derived. Combined with online CO2 and pressure measurements, molar gas balances of the cultivations were closed, and an anaerobic respiration quotient was calculated. Thus, insight into the effect of medium components and inhibitory cultivation conditions on H2 production with the model anaerobes was gained. The presented online H2 monitoring method can accelerate the characterization of anaerobes for biohydrogen production and reveal metabolic changes without expensive equipment and offline analysis.

Pd nanoparticles decorated SnO2 ultrathin nanosheets for highly sensitive H2 sensor: Experimental and theoretical studies

This study is attempted to improve the hydrogen sensing performance of SnO2 based sensors by simultaneously employing two strategies of morphology control and noble metal loading. Therefore, SnO2 ultrathin nanosheets with thickness not exceeding 3.5 nm were successfully synthesized by a hydrothermal method and then different content of Pd nanoparticles were uniformly loaded onto SnO2 surface by in situ reduction with ascorbic acid. The gas sensing properties demonstrated that the introduction of Pd not only altered the selectivity of the SnO2 sensor from ethanol to hydrogen, but also significantly improved the gas sensitivity and reduced the working temperature. And the optimal 1.0%Pd/SnO2 sensor owned the highest sensitivity (75), fastest response-recovery property (21 s/13 s) to 20 ppm of hydrogen at 220 °C, and the actual detection limit is as low as 0.1 ppm. Furthermore, 1.0%Pd/SnO2 sensor exhibited excellent repeatability, reproducibility and acceptable anti-interference of humidity. The DFT studies suggest that the physisorption of the hydrogen molecules on the surface of SnO2, but chemisorption on the surface of Pd/SnO2. The improved H2 sensing performance of Pd/SnO2 sensor attributes its ultrathin thickness of SnO2 and catalytic dissociation of Pd to O2 and H2.

Room-temperature response of MOF-derived Pd@PdO core shell/γ-Fe2O3 microcubes decorated graphitic carbon based ultrasensitive and highly selective H2 gas sensor

With the current upsurge in hydrogen economies all over the world, an increased demand for improved chemiresistive H2 sensors that are highly responsive and fast acting when exposed to gases is expected. Owing to safety concerns about explosive and highly flammable H2 gas, it is important to develop resistive sensors that can detect the leakage of H2 gas swiftly and selectively. Currently, interest in metal-organic frameworks (MOFs) for gas-sensor applications is increasing due to their open-metal sites, large surface area, and unique surface morphologies. In this research, a highly selective and sensitive H2-sensor was established based on graphitic carbon (GC) anchored spherical Pd@PdO core-shells over γ-Fe2O3 microcube (Pd@PdO/γ-Fe2O3@GC which is termed as S3) heterostructure materials. The combined solvothermal followed by controlled calcination-assisted S3 exhibited a specific morphology with the highest surface area of 79.12 m2 g−1, resulting in fast response and recovery times (21 and 29 s, respectively), and excellent sensing performance (ΔR/R0∼ 96.2 ± 1.5), outstanding long-term stability, and a 100 ppb detection limit when detecting H2-gas at room temperature (mainly in very humid surroundings). This result proves that adsorption sites provided by S3 can promote surface reactions (adsorption and desorption) for ultrasensitive and selective H2gas sensors.

Kinetics-Driven Dual Hydrogen Spillover Effects for Ultrasensitive Hydrogen Sensing.

Palladium (Pd)-modified metal oxide semiconductors (MOSs) gas sensors often exhibit unexpected hydrogen (H2 ) sensing activity through a spillover effect. However, sluggish kinetics over a limited Pd-MOS surface seriously restrict the sensing process. Here, a hollow Pd-NiO/SnO2 buffered nanocavity is engineered to kinetically drive the H2 spillover over dual yolk-shell surface for the ultrasensitive H2 sensing. This unique nanocavity is found and can induce more H2 absorption and markedly improve kinetical H2 ab/desorption rates. Meanwhile, the limited buffer-room allows the H2 molecules to adequately spillover in the inside-layer surface and thus realize dual H2 spillover effect. Ex situ XPS, in situ Raman, and density functional theory (DFT) analysis further confirm that the Pd species can effectively combine H2 to form Pd-H bonds and then dissociate the hydrogen species to NiO/SnO2 surface. The final Pd-NiO/SnO2 sensors exhibit an ultrasensitive response (0.1-1000ppm H2 ) and low actual detection limit (100 ppb) at the operating temperature of 230 °C, which surpass that of most reported H2 sensors.

Bulk-Processed Plasmonic Plastic Nanocomposite Materials for Optical Hydrogen Detection.

ConspectusSensors are ubiquitous, and their importance is only going to increase across many areas of modern technology. In this respect, hydrogen gas (H2) sensors are no exception since they allow mitigation of the inherent safety risks associated with mixtures of H2 and air. The deployment of H2 technologies is rapidly accelerating in emerging energy, transport, and green steel-making sectors, where not only safety but also process monitoring sensors are in high demand. To meet this demand, cost-effective and scalable routes for mass production of sensing materials are required. Here, the state-of-the-art often resorts to processes derived from the microelectronics industry where surface-based micro- and nanofabrication are the methods of choice and where (H2) sensor manufacturing is no exception.In this Account, we discuss how our recent efforts to develop sensors based on plasmonic plastics may complement the current state-of-the-art. We explore a new H2 sensor paradigm, established through a series of recent publications, that combines (i) the plasmonic optical H2 detection principle and (ii) bulk-processed nanocomposite materials. In particular, plasmonic plastic nanocomposite sensing materials are described that comprise plasmonic H2-sensitive colloidally synthesized nanoparticles dispersed in a polymer matrix and enable the additive manufacturing of H2 sensors in a cost-effective and scalable way. We first discuss the concept of plasmonic plastic nanocomposite materials for the additive manufacturing of an active plasmonic sensing material on the basis of the three key components that require individual and concerted optimization: (i) the plasmonic sensing metal nanoparticles, (ii) the surfactant/stabilizer molecules on the nanoparticle surface from colloidal synthesis, and (iii) the polymer matrix. We then introduce the working principle of plasmonic H2 detection, which relies on the selective absorption of H species into hydride-forming metal nanoparticles that, in turn, induces distinct changes in their optical plasmonic signature in proportion to the H2 concentration in the local atmosphere. Subsequently, we assess the roles of the key components of a plasmonic plastic for H2 sensing, where we have established that (i) alloying Pd with Au and Cu eliminates hysteresis and introduces intrinsic deactivation resistance at ambient conditions, (ii) surfactant/stabilizer molecules can significantly accelerate and decelerate H2 sorption and thus sensor response, and (iii) polymer coatings accelerate sensor response, reduce the limit of detection (LoD), and enable molecular filtering for sensor operation in chemically challenging environments. Based on these insights, we discuss the rational development and detailed characterization of bulk-processed plasmonic plastics based on glassy and fluorinated matrix polymers and on tailored flow-chemistry-based synthesis of Pd and PdAu alloy colloidal nanoparticles with optimized stabilizer molecules. In their champion implementation, they enable highly stable H2 sensors with response times in the 2 s range and an LoD of few 10 ppm of H2. To put plasmonic plastics in a wider perspective, we also report their implementation using different polymer matrix materials that can be used for 3D printing and (an)isotropic Au nanoparticles that enable the manufacturing of macroscopic plasmonic objects with, if required, dichroic optical properties and in amounts that can be readily upscaled. We advertise that melt processing of plasmonic plastic nanocomposites is a viable route toward the realization of plasmonic objects and sensors, produced by scalable colloidal synthesis and additive manufacturing techniques.

Palladium-Nanoparticle-Decorated Covalent Organic Framework Nanosheets for Effective Hydrogen Gas Sensors

Covalent organic frameworks (COFs) are attractive for chemical sensing applications because their structures contain delocalized π electrons and active sites that are evenly distributed. COF-based chemical sensors are largely restricted to luminescence and absorption-based mechanisms of sensing. The present study demonstrates the potentiality of exfoliated COF nanosheets hybridized with palladium nanoparticles (Pd NPs) for effective chemiresistive H2 sensing, for the first time. The hybridization of Pd NPs with the nanosheets of an imine-based covalent organic framework (ePd@TpPa-SO3H COF) has turned an innocent bulk COF into an effective chemiresistive H2 sensor.

MEMS sensor based on MOF-derived WO3-C/In2O3 heterostructures for hydrogen detection

Rational structure design of sensing materials is the most effective way to obtain a hydrogen (H2) sensor with optimal performance. Herein, a porous heterostructure WO3-C/In2O3 was designed and prepared by in-situ coupling carbon layer and WO3 into MOF-derived (metal organic framework) In2O3. In combination with Micro-Electro-Mechanical System (MEMS), a miniature H2 sensor using WO3-C/In2O3 as the active sensing material was fabricated. Compared with the bare In2O3 sensor, the sensor based on WCI-9 (the mass ratio of WO3 to In2O3 in WO3-C/In2O3 is 9 wt%) shows higher response value and lower operating temperature (Ra/Rg = 10.11@ 1000 ppm; 250 °C). Moreover, the WCI-9 sensor possesses a fast response-recovery speed (1.9/9.2 s@200 ppm) and a low limit of detection (LOD) (5 ppm) for H2. The good performance of the WCI-9 sensor is attributed to the hierarchical porous structure and multicomponent heterojunctions present in the material. This work not only provides an effective method for H2 detection, but also a strategy for constructing sensing materials with multicomponent heterojunctions.

Room Temperature Resistive Hydrogen Sensor for Early Safety Warning of Li-Ion Batteries

Lithium-ion batteries (LIBs) have become one of the most competitive energy storage technologies. However, the “thermal runaway” of LIBs leads to serious safety issues. Early safety warning of LIBs is a prerequisite for the widely applications of power battery and large-scale energy storage systems. As reported, hydrogen (H2) could be generated due to the reaction of lithium metal and polymers inside the battery. The generation of H2 is some time earlier than the “thermal runaway”. Therefore, the rapid detection of trace hydrogen is the most effective method for early safety warning of LIBs. Resistive hydrogen sensors have attracted attention in recent years. In addition, they could be placed inside the LIB package for the initial hydrogen detection. Here, we overview the recent key advances of resistive room temperature (RT) H2 sensors, and explore possible applications inside LIB. We explored the underlying sensing mechanisms for each type of H2 sensor. Additionally, we highlight the approaches to develop the H2 sensors in large scale. Finally, the present review presents a brief conclusion and perspectives about the resistive RT H2 sensors for early safety warning of LIBs.

Highly sensitive and wrappable room temperature wireless gasochromic and chemiresistive dual-response H2 sensors using spray coating

Developing highly reliable, sensitive and room temperature operation hydrogen (H2) sensors is essential to adapt successfully to the H2 economy. Despite the development of various H2 sensors, detecting leaks and pinpointing their precise location remains challenging because of the highly diffusive nature of H2 and environmental factors such as the wind direction. This study reports the development of room temperature, wireless, dual-signal, wrappable, chemiresistive, and eye-readable gasochromic H2 sensors using solution-based and low temperature annealed SnO2/WO3 films on polyimide substrate. These sensors can be wrapped around any point source, such as flanges, rendering the early detection and pinpointing of H2 leaks. An optimized spray-coated gasochromic WO3 film achieves a color change value (ΔE) of 11 with a 6 s response time at 4% H2 and low eye detectable limit of 0.2%. Simultaneously, because a patterned spray-coated gasochromic layer does not interfere with the active area of a SnO2-based chemiresistive sensor, the resistance value of the sensor changes by more than 11,000 times at 1% H2 with a wide concentration range from 0.005% to 2% of H2 at room temperature. Such a sensor can be easily applied to various nonplanar surfaces, while the Bluetooth system integration enables wireless monitoring via smartphones. Our study provides a simple strategy to develop wrappable dual-signal wireless sensors for reliable detection and monitoring of H2 leaks at room temperature.

PdRh-Sensitized Iron Oxide Ultrathin Film Sensors and Mechanistic Investigation by Operando TEM and DFT Calculation.

Metal oxide semiconductor (MOS) thin films are of critical importance to both fundamental research and practical applications of gas sensors. Herein, a high-performance H2 sensor based on palladium (Pd) and rhodium (Rh) co-functionalized Fe2 O3 films with an ultrathin thickness of 8.9nm deposited by using atomic layer deposition is reported. The sensor delivers an exceptional response of 105.9 toward 10ppm H2 at 230 °C, as well as high selectivity, immunity to humidity, and low detection limit (43 ppb), which are superior to the reported MOS sensors. Importantly, the Fe2 O3 film sensor under dynamic H2 detection is for the first time observed by operando transmission electron microscopy, which provides deterministic evidence for structure evolution of MOS during sensing reactions. To further reveal the sensing mechanism, density functional theory calculations are performed to elucidate the sensitization effect of PdRh catalysts. Mechanistic studies suggest that Pd promotes the adsorption and dissociation of H2 to generate PdHx , while Rh promotes the dissociation of oxygen adsorbed on the surface, thereby jointly promoting the redox reactions on the films. A wireless H2 detection system is also successfully demonstrated using the thin film sensors, certifying a great potential of the strategy to practical sensors.

Composition of the Gas-Air Mixture in the Containment and Suppression of Forest Fires with Promising Extinguishing Agents

This paper presents experimental research findings on the gas composition of pyrolysis and combustion products of typical forest fuels (leaves, needles, twigs, a mixture of these, and timber). These experiments were performed for the combustion and application of a fire extinguishing agent to a pyrolyzing material. Water, a bischofite solution, a bentonite slurry, and a foaming agent solution were utilized. Two gas analysis systems were used, as follows: an industrial one based on CO2, CO, H2, CH4, and O2 sensors and a scientific one (a gas analyzer with H2, CH4, H2S, SO2, CO, and CO2 sensors). Fires were extinguished by using two common techniques, as follows: continuous liquid supply and cycling spraying. The comparative efficiency of applying a group of fire extinguishing agents to forest fires was estimated, taking account of liquid consumption, suppression time, and environmental pollution. A method was proposed for calculating the relative efficiency factors of fire extinguishing agents when containing and suppressing forest fires, allowing for the consumed time, resources, and anthropogenic emissions.

Supraparticles for naked-eye H2 indication and monitoring: Improving performance by variation of the catalyst nanoparticles.

The recent transition to H2-based energy storage demands reliable H2 sensors that allow for easy, fast, and reliable detection of leaks. Conventional H2 detectors are based on the changes of physical properties of H2 probes induced by subsurface H-atoms to a material such as electrical conductivity. Herein, we report on highly reactive gasochromic H2 detectors based on the adsorption of H2 on the material surface. We prepared supraparticles (SPs) containing different types of noble metal nanoparticles (NPs), silica NPs, and the dye resazurin by spray-drying and tested their performance for H2 detection. The material undergoes a distinct color change due to the hydrogenation of the purple resazurin to pink resorufin and, finally, colorless hydroresorufin. The stepwise transition is fast and visible to the naked eye. To further improve the performance of the sensor, we tested the reactivity of SPs with different catalytically active NPs by means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). We show that the choice of the NP catalyst has a pronounced effect on the response of the H2 indicator. In addition, we demonstrate that the performance depends on the size of the NPs. These effects are attributed to the availability of reactive H-atoms on the NP surface. Among the materials studied, Pt-containing SPs gave the best results for H2 detection.

Ultrahigh-response sensor based on hierarchical Pd-WO3 nanoflowers for rapid hydrogen detection

In this research, four tungsten trioxide materials were synthesized in precursor solutions with different pH values by hydrothermal method. Then, Pd nanoparticles were loaded on the hierarchical WO3 nanoflowers, which exhibited the best hydrogen sensitivity among the four as-synthesized materials. The hydrogen sensing test results demonstrated that the 0.50 at% Pd-WO3 sensor showed a fairly high response of 8658.98, a fast response/recovery time of 1/3 s and excellent selectivity to 500 ppm H2 at a working temperature of 150 °C, which properties were superior to previous WO3-based hydrogen sensors. The wonderful H2 sensing property was shown due to the increase of oxygen vacancies, adjustment of basic sensor resistance and spill-over effect of Pd. This work will provide a feasible strategy for designing H2 sensors with a fairly high response and fast response/recovery speed.

An ultrasonically catalyzed conductometric metal oxide gas sensor system with machine learning-based ambient temperature compensation

The ultrasonic catalysis method provides a new means of enhancing sensing performance of some types of gas sensors. But generating the ultrasound consumes electric energy and increases the system mass. Thus, it is significant to lower the energy consumption and mass of the ultrasonic excitation structure as much as possible, while enhancing the sensing performance. In this work, a thin conical metal shell excited by a piezoelectric disk has been proposed, serving as the focusing ultrasonic transducer and protection case for a SnO2 gas sensor. The ultrasonic transducer’s total mass is only 11 g. The experiments show that the ultrasonic transducer can significantly reduce the low detection limit (LDL), and measured LDL of the sonicated sensor for H2 can be as low as 107 ppb (1/3 of the same sensing element not sonicated) with a response of 4.6%. In this case, the ultrasonic transducer’s power consumption and temperature rise is 146 mW and 3 ℃, respectively. The low temperature rise indicates that the LDL may be further decreased by increasing the ultrasonic vibration. The effect of ambient temperature change on predicted H2 concentration is compensated by two convolutional neural networks for the low (1–100 ppm) and ultralow (≤ 1 ppm) concentration ranges, and the relative error of concentration prediction in these two concentration ranges is 5.7% and 12.3%, respectively.

Toward a synthetic hydrogen sensor in cyanobacteria: Functional production of an oxygen-tolerant regulatory hydrogenase in Synechocystis sp. PCC 6803.

Cyanobacteria have raised great interest in biotechnology, e.g., for the sustainable production of molecular hydrogen (H2) using electrons from water oxidation. However, this is hampered by various constraints. For example, H2-producing enzymes compete with primary metabolism for electrons and are usually inhibited by molecular oxygen (O2). In addition, there are a number of other constraints, some of which are unknown, requiring unbiased screening and systematic engineering approaches to improve the H2 yield. Here, we introduced the regulatory [NiFe]-hydrogenase (RH) of Cupriavidus necator (formerly Ralstonia eutropha) H16 into the cyanobacterial model strain Synechocystis sp. PCC 6803. In its natural host, the RH serves as a molecular H2 sensor initiating a signal cascade to express hydrogenase-related genes when no additional energy source other than H2 is available. Unlike most hydrogenases, the C. necator enzymes are O2-tolerant, allowing their efficient utilization in an oxygenic phototroph. Similar to C. necator, the RH produced in Synechocystis showed distinct H2 oxidation activity, confirming that it can be properly matured and assembled under photoautotrophic, i.e., oxygen-evolving conditions. Although the functional H2-sensing cascade has not yet been established in Synechocystis yet, we utilized the associated two-component system consisting of a histidine kinase and a response regulator to drive and modulate the expression of a superfolder gfp gene in Escherichia coli. This demonstrates that all components of the H2-dependent signal cascade can be functionally implemented in heterologous hosts. Thus, this work provides the basis for the development of an intrinsic H2 biosensor within a cyanobacterial cell that could be used to probe the effects of random mutagenesis and systematically identify promising genetic configurations to enable continuous and high-yield production of H2 via oxygenic photosynthesis.

1ppm-detectable hydrogen gas sensors by using highly sensitive P+/N+ single-crystalline silicon thermopiles

Hydrogen (H2) is currently of strategic importance in the pursuit of a decarbonized, environmentally benign, sustainable global energy system; however, the explosive nature of H2 requires leakage monitoring to ensure safe application in industry. Therefore, H2 gas sensors with a high sensitivity and fast response across a wide concentration range are crucial yet technically challenging. In this work, we demonstrate a new type of MEMS differential thermopile gas sensor for the highly sensitive, rapid detection of trace H2 gas in air. Facilitated by a unique MIS fabrication technique, pairs of single-crystalline silicon thermopiles (i.e., sensing and reference thermopiles) are batch fabricated with high-density single-crystalline silicon thermocouples, yielding an outstanding temperature sensitivity at the sub-mK level. Such devices ensure the detection of miniscule temperature changes due to the catalytic reaction of H2 with a detection limit as low as ~1 ppm at an operating temperature of 120 °C. The MEMS differential thermopiles also exhibit a wide linear detection range (1 ppm-2%, more than four orders of magnitude) and fast response and recovery times of 1.9 s and 1.4 s, respectively, when detecting 0.1% H2 in air. Moreover, the sensors show good selectivity against common combustible gases and volatile organics, good repeatability, and long-term stability. The proposed MEMS thermopile H2 sensors hold promise for the trace detection and early warning of H2 leakage in a wide range of applications.

Room‐Temperature Hydrogen Sensor with High Sensitivity and Selectivity using Chemically Immobilized Monolayer Single‐Walled Carbon Nanotubes

AbstractAlthough semiconducting single‐walled carbon nanotubes (sc‐SWNTs) exhibit excellent sensing properties for various gases, commercialization is hampered by several obstacles. Among these, the difficulty in reproducibly fabricating sc‐SWNT films with uniform density and thickness is the main one. Here, a facile fabrication method for sc‐SWNT‐based hydrogen (H2) sensors with excellent reproducibility, high sensitivity, and selectivity against CO, CO2, and CH4 is reported. Uniform‐density and monolayer sc‐SWNT films are fabricated using chemical immobilized through the click reaction between azide‐functionalized polymer‐wrapped sc‐SWNTs and immobilized alkyne polymer on a substrate before decorating with Pd nanoparticles (0.5–3.0 nm). The optimized sc‐SWNT sensor has a high room‐temperature response of 285 with the response and recovery times of 10 and 3 s, respectively, under 1% H2 gas in air. In particular, this sensor demonstrates highly selective H2 detection at room temperature (25 °C), compared to other gases and humidity. Therefore, the chemical immobilization of the monolayer SWNT films with reproducible and uniform density has the potential for large‐scale fabrication of robust room‐temperature H2 sensors.

Polymerization-Induced Aggregation Approach toward Uniform Pd Nanoparticle-Decorated Mesoporous SiO2/WO3 Microspheres for Hydrogen Sensing

Hydrogen as an important clean energy source with a high energy density has attracted extensive attention in fuel cell vehicles and industrial production. However, considering its flammable and explosive property, gas sensors are desperately desired to efficiently monitor H2 concentration in practical applications. Herein, a facile polymerization-induced aggregation strategy was proposed to synthesize uniform Si-doped mesoporous WO3 (Si-mWO3) microspheres with tunable sizes. The polymerization of the melamine-formaldehyde resin prepolymer (MF prepolymer) in the presence of silicotungstic acid hydrate (abbreviated as H4SiW) leads to uniform MF/H4SiW hybrid microspheres, which can be converted into Si-mWO3 microspheres through a simple thermal decomposition treatment process. In addition, benefiting from the pore confinement effect, monodispersed Pd-decorated Si-mWO3 microspheres (Pd/Si-mWO3) were subsequently synthesized and applied as sensitive materials for the sensing and detection of hydrogen. Owing to the oxygen spillover effect of Pd nanoparticles, Pd/Si-mWO3 enables adsorption of more oxygen anions than pure mWO3. These Pd nanoparticles dispersed on the surface of Si-mWO3 accelerated the dissociation of hydrogen and promoted charge transfer between Pd nanoparticles and WO3 crystal particles, which enhanced the sensing sensitivity toward H2. As a result, the gas sensor based on Pd/Si-mWO3 microspheres exhibited excellent selectivity and sensitivity (Rair/Rgas = 33.5) to 50 ppm H2 at a relatively low operating temperature (210 °C), which was 30 times higher than that of the pure Si-mWO3 sensor. To develop intelligent sensors, a portable sensor module based on Pd/Si-mWO3 in combination with wireless Bluetooth connection was designed, which achieved real-time monitoring of H2 concentration, opening up the possibility for use as intelligent H2 sensors.

High selectivity and response H2 sensors based on ZnO@ZIF-71@Ag nanorod arrays

Hydrogen (H2) is widely used in industrial and medical, however its flammable and explosive nature requires economical and effective monitoring to ensure safety. In this work, ZnO@ZIF-71@Ag nanorod arrays were synthesized to provide an effective adsorption response to H2 through size effect and high catalytic activity by immobilizing Ag nanoparticles (NPs) into the pores of ZIF-71. The results of the gas sensitivity tests showed that the nanorod arrays were significantly more selective towards H2. Moreover, the response of ZnO@ZIF-71@Ag to 50 ppm H2 was 11 times higher than that of ZnO@ZIF-71 at a lower operating temperature (150°C). The size of the Ag NPs was demonstrated to be below 10 nm by TEM characterization, suggesting that Ag in the form of quantum dots (QDs) to bring an unignorable catalytic effect for breaking hydrogen molecule (H2) into highly active atoms ([H]). In addition, the result of Density Function Theory (DFT) calculation revealed that the adsorption energy of Ag-catalyzed [H] (−8.255 eV) was much higher than that of H2 (−4.222 eV) on ZnO (100), which results in elevated charge transfer to promote hydrogen sensing performance of ZnO@ZIF-71@Ag. In this study, a novel hydrogen sensor based on pore sieving and catalytic sensing mechanisms was obtained, which provides a new reference for the development of hydrogen sensors.

Ultra-fast and sensitive magneto-optical hydrogen sensors using a magnetic nano-cap array

Magnetism in curved nano-geometries has opened a new path to design novel characteristics and phenomena that could greatly impact the future fundamental and applied studies of materials. In this report, a hexagonally-packed array of magnetic nano-caps (or nano-patches, NP) exhibiting unique magnetic anisotropy and optimal nanostructure for fast hydrogen kinetics is explored as a sensing element for the spark-free magnetic-circular-dichroism (MCD) H2 sensor. The MCD H2 sensor outperforms the state-of-the-art optical sensors reported to date and satisfies the most challenging performance targets imposed by US Department of Energy. In particular, a Pd67Co33 NP sensor exhibits response time of t90 < 0.9 s, recovery time of t10 < 9.0 s over the 1–100 mbar H2 partial pressure range, and limit of detection (LOD) of ∼1 ppm. The LOD improves to < 700 ppb, when the signal-to-noise ratio is enhanced by stacking three NP arrays. Using a 30-nm TAF (Teflon AF 2400) polymer coating, the sorption kinetics of the Pd67Co33/TAF sensor are significantly accelerated, with t90 < 0.4 s and t10 < 2.8 s over the same pressure range. When the Pd67Co33/TAF sensor is further coated with a 100-nm poly(methyl methacrylate) (PMMA) layer, a rapid sorption time of t90 < 0.5 s, LOD < 1 ppm and excellent sensor accuracy (<2.5% full scale) are maintained, while the sensor obtains strong selectivity against interference gases and moisture, and a negligible aging effect. The MCD nano-cap sensor platform may have a great impact on the future deployment of H2 fuel, environmental monitoring H2 sensors, and fast proton-based magneto-ionic devices.