Room Temperature H2 Research Articles

Characterization and Modeling of a Pt-In2O3 Resistive Sensor for Hydrogen Detection at Room Temperature.

Sensitive H2 sensors at low concentrations and room temperature are desired for the early warning and control of hydrogen leakage. In this paper, a resistive sensor based on Pt-doped In2O3 nanoparticles was fabricated using inkjet printing process. The H2 sensing performance of the sensor was evaluated at low concentrations below 1% at room temperature. It exhibited a relative high response of 42.34% to 0.6% H2. As the relative humidity of 0.5% H2 decreased from 34% to 23%, the response decreased slightly from 34% to 23%. The sensing principle and the humidity effect were discussed. A dynamic current sensing model for dry H2 detection was proposed based on Wolkenstein theory and experimentally verified to be able to predict the sensing behavior of the sensor. The H2 concentration can be calculated within a short measurement time using the model without waiting for the saturation of the response, which significantly reduces the sensing and recovery time of the sensor. The sensor is expected to be a promising candidate for room-temperature H2 detection, and the proposed model could be very helpful in promoting the application of the sensor for real-time H2 leakage monitoring.

The application of nonthermal plasma in methanol synthesis via CO2 hydrogenation

AbstractCH3OH is an energy carrier that can be generated from renewable resources and be used as a fuel in fuel cells and internal combustion engines and a platform chemical for the synthesis of value‐added chemicals or gasoline. Carbon dioxide (CO2) hydrogenation is one of the widely researched methods to generate methanol. The traditional CO2 hydrogenation reaction method (requires high H2 pressure and temperatures) has attracted considerable attention. However, the new emerging field of catalysis referred to as nonthermal plasma (NTP) catalysis has also been developed extensively for methane reforming and CO2 hydrogenation to methane and CO. The plasma‐assisted approach not only presents remarkable advantages, such as room temperature and atmospheric H2 pressure but also has great potential to be powered by renewable electricity in a flexible way since it can be easily switched on/off. In this account, we review the recent articles published on methanol synthesis from CO2 and H2 using NTP. We reviewed and discussed the mechanism of this reaction under NTP, the modification of the reactor configurations, and the rationale behind the catalyst design. In the end, we discussed the advantages and disadvantages of each of these works and the future perspectives of this interesting privileged reaction. We believe this review is of interest to researchers active in sustainable heterogeneous catalysis.

Reversible Room Temperature H2 Gas Sensing Based on Self-Assembled Cobalt Oxysulfide.

Reversible H2 gas sensing at room temperature has been highly desirable given the booming of the Internet of Things (IoT), zero-emission vehicles, and fuel cell technologies. Conventional metal oxide-based semiconducting gas sensors have been considered as suitable candidates given their low-cost, high sensitivity, and long stability. However, the dominant sensing mechanism is based on the chemisorption of gas molecules which requires elevated temperatures to activate the catalytic reaction of target gas molecules with chemisorbed O, leaving the drawbacks of high-power consumption and poor selectivity. In this work, we introduce an alternative candidate of cobalt oxysulfide derived from the calcination of self-assembled cobalt sulfide micro-cages. It is found that the majority of S atoms are replaced by O in cobalt oxysulfide, transforming the crystal structure to tetragonal coordination and slightly expanding the optical bandgap energy. The H2 gas sensing performances of cobalt oxysulfide are fully reversible at room temperature, demonstrating peculiar p-type gas responses with a magnitude of 15% for 1% H2 and a high degree of selectivity over CH4, NO2, and CO2. Such excellent performances are possibly ascribed to the physisorption dominating the gas–matter interaction. This work demonstrates the great potentials of transition metal oxysulfide compounds for room-temperature fully reversible gas sensing.

Reversible hydrogen storage on alkali metal (Li and Na) decorated C20 fullerene: A density functional study

This work reports the reversible hydrogen storage capacities of Li and Na decorated C20 fullerene using dispersion corrected density functional theory calculation. The alkali metal (AM) atoms are found to bind on the C–C bridge position of C20 through non-covalent closed-shell interaction. Their thermodynamic stabilities are verified through HOMO-LUMO gaps and different reactivity descriptors. Each Li and Na atoms decorated on C20 adsorb maximum up to five H2 molecules through Niu-Rao-Jena interaction. The adsorption energy decreases with successive addition of H2 molecules with average binding energy lying in the range of 0.12 eV–0.13 eV. The systems can have a maximum gravimetric density of 13.08 wt% and 10.82 wt% for C20Li4–20H2 and C20Na4–20H2 respectively. ADMP molecular dynamic simulations illustrate the reversibility of adsorbed hydrogen molecules at higher temperature (≧ 300 K). The calculated thermodynamic useable hydrogen capacity shows the room temperature H2 desorption condition of AM decorated C20. Consistent with criteria set by the US-DOE, C20Li4 and C20Na4 can be used as promising hydrogen storage materials.

Reduced Graphene Oxide-Wrapped Palladium Nanowires Coated with a Layer of Zeolitic Imidazolate Framework-8 for Hydrogen Sensing

Rapid and sensitive H2 detection is important because of its low threshold for the formation of explosive mixtures in air (∼4%). Palladium’s unique interactions with H2 make it particularly useful in room-temperature H2 sensing, but the formation of water by reaction with O2 at the Pd surface can interfere with sensor response. Here, we report H2 sensors using networks of high aspect ratio and ultrathin reduced graphene oxide (rGO)-coated palladium nanowires (Pd NWs@rGO) with a coating of zeolite imidazole framework (ZIF-8) that serves as a nanofiltration layer. We first produced Pd NWs in high yield by a hydrothermal method, then sonicated them with GO and added a reducing agent to produce Pd NWs@rGO. Thin Pd NWs promote rapid response and high sensitivity, while rGO prevents the formation of additional conductive channels due to expansion of Pd NWs upon H2 exposure, ensuring monotonic sensor response. The coating of ZIF-8 reduces the transport of molecules like oxygen and nitrogen to the Pd NWs while allowing H2 to reach them and H2O to diffuse away from them. The optimized sensors showed a response (relative change in resistance) to 1% H2 in air of up to 2%, with a response time of 5 s and a lower limit of detection of 20 ppm. Relative to previously reported Pd-based H2 sensors with fast response, the Pd NWs@rGO@ZIF-8 nanocomposite-based device provides a low-cost, high-performance sensor solution for fuel-cell vehicles and similar applications that require both rapid and sensitive H2 detection.

Alkylamine-Grafted Organic Semiconductors with Plasma-Induced Defects as Electron Promoters of CO-Resistant Pd-Based Nanoparticles for Efficient Light-Driven On-Demand H2 Generation

Tailoring the adsorption characteristics of catalytic substrates and the electronic behavior of catalytically active species in heterogeneous catalysts is beneficial for regulating their catalytic performance. Herein, we report a highly efficient room-temperature photocatalytic formic acid (HCOOH) dehydrogenation system, where plasma-induced carbon nitrides (CNs) grafted by aminosilanes are used as electron promoters of catalytically active AuPdM (M = Ni and Co) nanoparticles (NPs). The various characterizations verify that the plasma-induced CNs have rich nitrogen defects and the efficient separation of photogenerated charge carriers. The visible-light-driven synergism of alkylamine and defective CNs with tunable band structures in the catalysts accounts for their enhanced HCOOH adsorption and the enriched electron density of metal NPs. This indicates that the catalysts have 100% H2 selectivity and higher activities under visible light irradiation than in the dark. The optimal CO-resistant AuPdNi catalyst possesses 66.9% of apparent quantum yield at 420 nm and exhibits the record room-temperature H2 generation activity with the total turnover frequencies of 1075 and 1278 h–1 in the absence and presence of scavenger of photogenerated holes, respectively.

Holey engineered 2D ZnO-nanosheets architecture for supersensitive ppm level H2 gas detection at room temperature

Conquering the issue of room temperature H2 detection at ppm/ppb level and their fundamental sensing mechanism are vitally needed for the development of highly sensitive/selective sensing devices. Herein, a strategy is proposed to synthesize 2D ZnO holey nanosheets by engineering the tunable pore/hole size with controlled oxygen vacancies using the annealing process for H2 detection at room temperature. 2D ZnO holey nanosheets annealed at 400 °C shows a highly porous network owing to its high surface area, more channels for gas diffusion, and mass transport that exhibits improved gas-sensing performance. ZnO@400 sensor exhibits maximum response of ∼115 (20 times more than ZnO@800 sample) towards 100 ppm of H2 at room temperature. The sensor response (recovery) times of the order ∼9(6) secs recorded to be fastest for ZnO@400 sensor as compared to ZnO@600 (∼19(13) secs) and ZnO@800 (∼27(20) secs) sensor respectively. Further, the ZnO@400 sensor also displays superior repeatability and stability of ∼97−99% after 45 days. The involved gas sensing mechanism has also been verified by carrying out XPS measurements before and after H2 exposure at room temperature that helps to complement the theoretical justification about room temperature metallization effect. Thus, 2D ZnO holey nanosheets turn out to be a pivotal strategy to improve the gas sensing performance due to the synergetic effect of highly porous network and large specific surface areas of 2D nanosheets. The present approach proves to be one of the best methodologies to alleviate the restacking issue of the 2D nanosheets by opening up the inaccessible surfaces.

Fabrication of highly responsive room temperature H2 sensor based on vertically aligned edge-oriented MoS2 nanostructured thin film functionalized by Pd nanoparticles

The increasing use of hydrogen (H2) as a clean energy carrier utilized in the next-generation fuels demand parallel development of low power hydrogen sensors (operated at room temperature) for safety purposes. In this work, we report a controlled single-step, large-area growth of vertically aligned edge-oriented MoS2 hybrid nanostructured thin film decorated with Pd nanoparticles (Pd/MoS2) on quartz and Si substrates using DC magnetron sputtering technique. The structural, morphological, and chemical characterizations were performed using XRD, Raman, FESEM, TEM, EDX, and XPS techniques, which confirms the formation of Pd/MoS2 hybrid thin film. Hydrogen gas sensing characteristics of Pd/MoS2 hybrid thin film sensor under low detection range (10−500 ppm) and proposed sensing mechanism are discussed in detail. To gain further insights into the gas sensing mechanism, we have studied the junction band alignment at the Pd/MoS2 interface using ultraviolet photoelectron spectroscopy and ellipsometry. The results demonstrate that the fabricated Pd/MoS2 hybrid thin film sensor exhibits highly enhanced H2 sensing properties (decent response ∼33.7 %, fast response/recovery time ∼16 s/38 s, and higher selectivity) compared to pristine MoS2 thin film sensor (poor response ∼1.2 % and slow response/recovery time ∼29 s/158 s, and poor selectivity) towards 500 ppm H2 at room temperature (30 °C). Thus, this study offers the development of low power H2 sensors with enhanced sensor characteristics, which could be utilized in IoT (Internet of Things) network, with an advantage of facile and scalable fabrication techniques.

Pd-decorated 2D SnSe ultrathin film on SiO2/Si for room-temperature hydrogen detection with ultrahigh response

Developing hydrogen sensors with high integration and high performance is still a great challenge. Herein, two dimensional (2D) layered tin monoselenide (SnSe) ultrathin films are deposited on SiO2-buffered silicon substrates via a scalable sputtering method. Then, a 15-nm-thickness Pd layer is decorated on the SnSe film. Due to the anisotropic van der Waals force from 2D SnSe surface, large quantities of nanoscaled Pd grains are formed, largely enhancing the active area when exposed in gas molecules. Benefiting from the unique surficial structure and abrupt interfacial properties with a large built-in electrical field, the fabricated Pd-decorated SnSe/SiO2/Si heterojunction exhibits excellent room-temperature H2 sensing performance with an ultrahigh response of ∼3225, 2–3 orders of magnitude higher than other 2D-based sensors. The sensor device also achieves fast response/recovery speed (73.1/23.7 s), ultralow detecting limit (∼0.91 ppb), as well as good selectivity. These findings promise the great potential of Pd-decorated SnSe/SiO2/Si heterostructures for high-performance sensor applications.

Room temperature SO2 and H2 gas sensing using hydrothermally grown GO–ZnO nanorod composite films

Graphene based 2D materials with a surfeit of active sites and advantageously high surface to volume ratio are effectively linked to well established nanostructured semiconducting metal oxides for development of nanocomposites with enhanced gas sensing properties. Graphene Oxide (GO), a sister material of graphene, is therefore a natural choice for development of room temperature operated gas sensors. In the current investigation hydrothermally grown GO and ZnO nanorods composite (GO–ZnO–NR) is utilised for room temperature gas sensing of H2 and SO2 gases. Room temperature detection of H2 and SO2 at sub-100 ppm levels with linear variation in response for different concentrations is demonstrated. Morphological and structural analyses are conducted using Scanning electron microscopy, Raman spectroscopy and X-ray diffraction. GO-ZnO-NR composite sensor is seen to exhibit robust sensing response of 5.82 and 5.45 for 100 ppm each of H2 and SO2 gases respectively at room temperature. Further, the delayed response and recovery times exhibited by the sensor for SO2 gas are recognized to be due to formation of strongly adhering SO3 species.

Highly selective and ultra-low power consumption metal oxide based hydrogen gas sensor employing graphene oxide as molecular sieve

The excellent gas sensing performance of metal oxide based nano- and microstructures, including a fast response time and good sensitivity, is typically limited by their low selectivity. Therefore, novel approaches and strategies are required to gain a precise control of the selectivity. Here, we introduce a nanoporous few-layer graphene oxide (GO) membrane with permeability only to specific gas molecules to improve the selectivity of individual zinc oxide microwires (ZnO MWs) toward hydrogen (H2) gas. The fabricated GO-covered ZnO MWs showed ultra-low power consumption (60−200 nW) and an excellent room temperature H2 gas sensing properties with fast response (114 s) and recovery (30 s) times, and a low detection limit of ∼4 ppm, while no gas response was measured to all other tested gases. As proposed, the gas sensing mechanism is based on selective sieving of H2 gas molecules through the GO membrane and further diffusion to the Schottky contacts, resulting in a decreased barrier height. Being based on a bottom-up fabrication approach, the presented results could have great potential for further technological applications such as high-performance and highly selective ultra-low power metal oxide-based gas sensors, opening new opportunities for the design of nanosensors and their integration in wireless and portable devices.

Promoting Effect of Heterostructured NiO/Ni on Pt Nanocatalysts toward Catalytic Hydrolysis of Ammonia Borane.

We report that heterostructured NiO/Ni nanoparticles remarkably promote the catalytic H2 production of platinum (Pt) nanoclusters toward the hydrolysis of ammonia borane (AB). A hybrid nanocatalyst composed ultrasmall Pt nanoclusters, heterostructured NiO/Ni nanoparticles, and a carbon nanotube support (defined as Pt@NiO/Ni-CNT) is fabricated. The resultant Pt@NiO/Ni-CNT is highly efficient for room-temperature H2 production toward catalytic hydrolysis of AB, better than the Pt@NiO-CNT and Pt@Ni-CNT with NiO or Ni alone, and the Pt@NiO/Ni without CNT support. Optimal Pt@NiO/Ni-CNT catalyst exhibits a good catalytic activity with a high TOF of 2665 molH2 molPt-1 min-1 under ambient conditions, overtaking the activities of previously reported catalysts for AB hydrolysis. Catalytic kinetic studies indicate that compositional and structural features of the Pt@NiO/Ni-CNT synergistically accelerate the oxidative clearage of the H-OH bond from attacked H2O (the rate-determining step), thus boosting catalytic hydrolysis of AB kinetically.

Systematic uncertainty due to background-gas collisions in trapped-ion optical clocks

We describe a framework for calculating the frequency shift and uncertainty of trapped-ion optical atomic clocks caused by background-gas collisions, and apply this framework to an 27Al+ clock to enable a total fractional systematic uncertainty below 10-18. For this clock, with 38(19) nPa of room-temperature H2 background gas, we find that collisional heating generates a non-thermal distribution of motional states with a mean time-dilation shift of order 10-16 at the end of a 150 ms probe, which is not detected by sideband thermometry energy measurements. However, the contribution of collisional heating to the spectroscopy signal is highly suppressed and we calculate the BGC shift to be -0.6(2.4) × 10-19, where the shift is due to collisional heating time dilation and the uncertainty is dominated by the worst case ±π/2 bound used for collisional phase shift of the 27Al+ superposition state. We experimentally validate the framework and determine the background-gas pressure in situ using measurements of the rate of collisions that cause reordering of mixed-species ion pairs.

Stabilization of palladium nanoparticles on chitosan derived N-doped carbon for hydrogenation of various functional groups

We report the synthesis of uniformly dispersed and stable palladium nanoparticles (Pd NPs) on N-doped graphitic carbon (N-C) derived from benign chitosan. The Pd@N-C nanocatalyst was synthesized by carbonization of Pd-chitosan complex at 800 °C under a nitrogen atmosphere, wherein chitosan obtained from fishery bio-waste served as carbon and nitrogen source. The as-synthesized nanocatalyst was characterized by several techniques; the elemental mapping by SEM and TEM analysis confirmed the uniform distribution of the Pd nanoparticles on the surface of N-doped carbon with an average size in the range of 2–6 nm. Temperature programmed chemisorption studies showed 32.27% Pd metal surface area available for reaction. This catalyst with low loading of active palladium metal was used for the hydrogenation of various reducible groups including >C=C<, >C≡C<, -NO2, -CHO and epoxides at room temperature (30 °C) and moderate H2 pressure (5 bar). The catalyst offered nearly complete conversion with >99% selectivity towards desired product. The excellent performance of the catalyst may be attributed to the dual role of N-rich carbon source which acts as a stabilization platform for palladium nanoparticles and also provides a basic environment. Furthermore, the catalyst can be easily recovered and recycled for five cycles without any significant loss in catalytic activity and selectivity.

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

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

Room temperature H2 plasma treatment for enhanced passivation of silicon/TiO2 interface

Simultaneous requirement of excellent interface passivation and low thermal budget is a desirable feature for low cost Si based carrier selective solar cells. Accordingly, Titanium dioxide (TiO2), a widely used electron selective material, finds challenges related to thermal annealing like phase change and compatibility with thermal budget of hole transport layers. To address this, here we report a H2 plasma treatment process at room temperature which significantly reduces the surface recombination velocity (∼40 cm/s). Consequently, the reverse saturation current of the Si-TiO2 diode improves by a factor of 40, built-in potential improves by 100 mV, and the diode exhibits a near unity ideality factor. Using the same method, our Si-based double heterojunction solar cell results in an absolute increase of 2.4% in efficiency over devices with conventional thermal annealing. Given the ease of implementation and excellent performance, the proposed method is a promising alternative to thermal annealing for Si based heterojunction devices.

ZnAl2O4‐Functionalized Zinc Oxide Microstructures for Highly Selective Hydrogen Gas Sensing Applications

In this work, a simple method of ZnAl2O4‐functionalization of ZnO microstructures is presented. The different characterization methods (structural, chemical, and micro‐Raman) demonstrated the presence of only ZnO and ZnAl2O4 crystalline phases. ZnAl2O4 nano‐crystallites grow on the surfaces of ZnO 3D microstructures having diameters of 50–100 nm and with high density. Transmission electron microscopy (TEM) and high‐resolution TEM (HRTEM) results clearly show ZnAl2O4 crystallites functionalizing zinc oxide tetrapod arms. The individual structures (microwires (MWs) and three‐dimensional (3D) tetrapods (Ts)) are integrated into functional devices, suitable for gas sensing applications. All devices show excellent hydrogen gas selectivity at relatively low operating temperature in the range of 25–100 °C. The highest gas sensing performances are obtained based on individual ZnAl2O4‐functionalized ZnO tetrapods (ZnAl2O4/ZnO‐T, with an arm diameter (D) of ≈400 nm) and a response of ≈2 at 25 °C to 100 ppm of hydrogen gas (H­2), while a ZnAl2O4/ZnO‐MW (D ≈ 400 nm) shows only a response of ≈1.1. The Al‐doped ZnO MW (D ≈ 400 nm) without ZnAl2O4 elaborated in another work, chosen only for comparison reason, shows no response up to 800 ppm H2 gas concentration. A gas sensing mechanism is proposed for a single ZnAl2O4/ZnO‐T microstructure based sensor. The obtained results on ZnAl2O4/ZnO‐T‐based devices is superior to many reported performances of other individual metal oxide nanostructures with much lower diameter, showing promising results for room temperature H2 gas sensing applications.

Room temperature response and enhanced hydrogen sensing in size selected Pd-C core-shell nanoparticles: Role of carbon shell and Pd-C interface

In the present work, the effect of carbon shell around size selected palladium (Pd) nanoparticles on hydrogen (H2) sensing has been studied by investigating the sensing response of Pd-C core-shell nanoparticles having a fixed core size and different shell thickness. The H2 sensing response of sensors based on Pd and Pd-C nanoparticles deposited on SiO2 and graphene substrate has been measured over a temperature range of 25 °C–150 °C. It is observed that Pd-C nanoparticle sensor shows higher sensitivity with increase in shell thickness and faster response/recovery in comparison to that of Pd nanoparticle samples. Pd-C nanoparticles show room temperature H2 sensitivity in contrast to Pd nanoparticles which respond only at higher temperatures. Role of carbon shell is also understood by investigating H2 sensing properties of Pd and Pd-C nanoparticles on graphene substrates. These results show that higher catalytic activity and electronic interaction at Pd-C interface, a complete coverage and protection of Pd surface by carbon and presence of structural defects in nanoparticle core are important for room temperature and higher sensing response.

Room-Temperature H₂ Gas Sensing Characterization of Graphene-Doped Porous Silicon via a Facile Solution Dropping Method.

In this study, a graphene-doped porous silicon (G-doped/p-Si) substrate for low ppm H2 gas detection by an inexpensive synthesis route was proposed as a potential noble graphene-based gas sensor material, and to understand the sensing mechanism. The G-doped/p-Si gas sensor was synthesized by a simple capillary force-assisted solution dropping method on p-Si substrates, whose porosity was generated through an electrochemical etching process. G-doped/p-Si was fabricated with various graphene concentrations and exploited as a H2 sensor that was operated at room temperature. The sensing mechanism of the sensor with/without graphene decoration on p-Si was proposed to elucidate the synergetic gas sensing effect that is generated from the interface between the graphene and p-type silicon.

Excellent Selectivity with High Conversion in the Semihydrogenation of Alkynes using Palladium‐Based Bimetallic Catalysts

AbstractA series of active‐carbon‐supported PdPb and PdCu bimetal catalysts were prepared for the selective semihydrogenation of alkynes in the liquid phase. The Pd0.33Pb0.67/C catalyst showed the best performance for various alkynes under mild reaction conditions (room temperature and ambient H2 pressure) and achieved 100 % conversion with 98 % selectivity to alkenes. In particular, over‐hydrogenation was avoided at complete alkyne conversion.