Theoretical prediction of structure,electronic and optical properties of VH2 hydrogen storage material

The vanadium hydrides have better hydrogen storage capacity in comparison to the other metal hydrides. Although the structure of VH₂ hydride has been reported, the structural stability, electronic and optical properties of VH₂ hydride are unclear. To solve these problems, we apply the first-principles method to study the structural stability, electronic and optical properties of VH₂ hydrides. Similar to the metal dihydrides, four possible VH₂ hydrides such as the cubic (Fm-3m), tetragonal (I4/mmm), tetragonal (P4₂/mnm) and orthorhombic (Pnma) are designed. The result shows that the cubic VH₂ hydride is a thermodynamic and dynamical stability. In particular, the tetragonal (I4/mmm) and the orthorhombic (Pnma) VH₂ hydrides are firstly predicted. It is found that these VH₂ hydrides show metallic behavior. The electronic interaction of V (d-state)-H (s-state) is beneficial to improve the hydrogen storage in VH₂ hydride. In addition, the formation of V–H bond can improve the structural stability of VH₂ hydride. Based on the analysis of optical properties, it is found that all VH₂ hydrides show the ultraviolet response. Compared to the tetragonal and orthorhombic VH₂ hydrides, the cubic VH₂ hydride has better storage optical properties. Therefore, we believe that the VH₂ hydride is a promising hydrogen storage material.     

Density functional theory study of the hydrogen evolution reaction in haeckelite boron nitride quantum dots

To satisfy arising energy needs and to handle the forthcoming worldwide climate transformation, the major research attention has been drawn to environmentally friendly, renewable and abundant energy resources. Hydrogen plays an ideal and significant role is such resources, due to its non-carbon based energy and production through clean energy. In this work, we have explored catalytic activity of a newly predicted haeckelite boron nitride quantum dot (haeck-BNQD), constructed from the infinite BN sheet, for its utilization in hydrogen production. Density functional theory calculations are employed to investigate geometry optimization, electronic and adsorption mechanism of haeck-BNQD using Gaussian16 package, employing the hybrid B3LYP and wB97XD functionals, along with 6–31G(d,p) basis set. A number of physical quantities such as HOMO/LUMO energies, density of states, hydrogen atom adsorption energies, Mulliken populations, Gibbs free energy, work functions, overpotentials, etc., have been computed and analysed in the context of the catalytic performance of haeck-BNQD for the hydrogen-evolution reaction (HER). Based on our calculations, we predict that the best catalytic performance will be obtained for H adsorption on top of the squares or the octagons of haeck-BNQD. We hope that our prediction of most active catalytic sites on haeck-BNQD for HER will be put to test in future experiments.     

Recent advances in electrocatalysts for seawater splitting in hydrogen evolution reaction

Electrocatalytic water splitting is an important method to produce green and renewable hydrogen (H₂). One of the hindrances for wide applications of electrocatalysis in H₂ production is the lack of freshwater resources. Comparatively, seawater splitting has become an effective approach for large-scale H₂ production due to its abundant reserves. However, the increased complexity of seawater content emerged more problems in electrocatalytic seawater splitting. Recently, various strategies have been reported on improving the performance of electrocatalysts applied in seawater. Herein, this review firstly analyzed the mechanisms and challenges of electrocatalytic seawater splitting to evolve H₂, and summarized the recent progress on H₂ production in electrocatalytic seawater splitting. Furthermore, suggestions for future work have been provided for guidance.     

Economic competitiveness of compact steam methane reforming technology for on-site hydrogen supply: A Foshan case study

On-site hydrogen production through steam-methane reforming (SMR) from city gas or natural gas is believed to be a cost-effective way for hydrogen-based infrastructure due to high cost of hydrogen transportation. In recent years, there have been a lot of on-site hydrogen fueling stations under design or construction in China. This study introduces current developments and technology prospects of skid-mounted SMR hydrogen generator. Also, technical solutions and economic analysis are discussed based on China's first on-site hydrogen fueling station project in Foshan. The cost of hydrogen product from skid-mounted SMR hydrogen generator is about 23 CNY/kg with 3.24 CNY/Nm³ natural gas. If hydrogen price is 60 CNY/kg, IRR of on-site hydrogen fueling station project reaches to 10.8%. While natural gas price fall to 2.3 CNY/Nm³, the hydrogen cost can be reduced to 18 CNY/kg, and IRR can be raised to 13.1%. The conclusion is that skid-mounted SMR technology has matured and is developing towards more compact and intelligent design, and will be a promising way for hydrogen fueling infrastructures in near future.     

New horizon in mechanochemistry—high-temperature,high-pressure mechanical synthesis in a planetary ball mill—with magnesium hydride synthesis as an example

A new route of materials synthesis, namely, high-temperature, high-pressure reactive planetary ball milling (HTPRM), is presented. HTPRM allows for the mechanosynthesis of materials at fully controlled temperatures of up to 450 °C and pressures of up to 100 bar of hydrogen. As an example of this application, a successful synthesis of magnesium hydride is presented. The synthesis was performed at controlled temperatures (room temperature (RT), 100, 150, 200, 250, 300, and 325 °C) while milling in a planetary ball mill under hydrogen pressure ($>$50 bar). Very mild milling conditions (250 rpm) were applied for a total milling time of 2 h, and a milling vial with a relatively small diameter (φ = 53 mm, V = ～0.06 dm³) was used. The effect of different temperatures on the synthesis kinetics and outcome were examined. The particle morphology, phase composition, reaction yield, and particle size were measured and analysed by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC) techniques. The obtained results showed that increasing the temperature of the process significantly improved the reaction rate, which suggested the great potential of this technique for the mechanochemical synthesis of materials.     

Robust optimal operation of continuous catalytic reforming process under feedstock uncertainty

The continuous catalytic regenerative (CCR) reforming process is one of the most significant sources of hydrogen production in the petroleum refining process. However, the fluctuations in feedstock composition and flow rate could significantly affect both product distribution and energy consumption. In this study, a robust deviation criterion based multi-objective optimization approach is proposed to perform the optimal operation of CCR reformer under feedstock uncertainty, with simultaneous maximization of product yields and minimization of energy consumption. Minimax approach is adopted to handle these uncertain objectives, and the Latin hypercube sampling method is then used to calculate these robust deviation criteria. Multi-objective surrogate-based optimization methods are next introduced to effectively solve the robust operational problem with high computational cost. The level diagram method is finally utilized to assist in multi-criteria decision-making. Two robust operational optimization problems with different objectives are solved to demonstrate the effectiveness of the proposed method for robust optimal operation of the CCR reforming process under feedstock uncertainty.     

Experimental study and model predictions on helium release in an enclosure with single or multiple vents

This paper presents experiments performed at Canadian Nuclear Laboratories (CNL) to examine the dispersion behaviour of helium in a polycarbonate enclosure that was representative of a residential parking garage. The purpose was to gain a better understanding of the effect of buoyancy- or wind-driven natural ventilation on hydrogen dispersion behaviour. Although hydrogen dispersion studies have been reported extensively in the literature, gaps still exist in predictive methods for hazard analysis. Helium, a simulant for hydrogen, was injected near the centre of the floor with a flow rate ranging from 5 to 75 standard litres per minute through an upward-facing nozzle, resulting in an injection Richardson number ranging between 10^?1 and 10². The location of the nozzle varied from the bottom of the enclosure to near the ceiling to examine the impact of the nozzle elevation on the development of a stratified layer in the upper region of the enclosure. When the injection nozzle was placed at a sufficiently low elevation, the vertical helium profile always consisted of a homogenous layer at the top overlaying a stratified layer at the bottom. To simulate outdoor environmental conditions, a fan was placed in front of each vent to examine the effect of opposing or assisting wind on the dispersion. The helium transients in the uniform layer predicted with analytical models were in good agreement with the measured transients for most tests. Model improvements are required for adequately predicting transients with primarily stratified profiles or strong opposing wind.     

Experimental research on combined effect of obstacle and local spraying water fog on hydrogen/air premixed explosion

In order to reveal the mechanism of water fog explosion suppression and research the combined effect of water fog and obstacle on hydrogen/air deflagration, multiple sets of experiments were set up. The results show that the instability of thermal diffusion under lean combustion conditions is the main influencing factor of hydrogen/air flame surface instability, and the existence of water fog will aggravate the hydrogen/air flame surface instability. When obstacle is not considered, 8 μm, 15 μm, 30 μm water fog can significantly reduce the flame velocity and explosion overpressure of hydrogen/air, 45 μm fine water fog plays the opposite role. When considering the relative position of the water fog release position and the obstacle, the 8 μm, 15 μm, 30 μm water fog has almost no suppression effect when released near the obstacle, but a significant suppression effect occur, when using the 45 μm water fog. In the field of theoretical research, the research results not only provide an experimental basis for the fine water fog to reduce the consequences of hydrogen explosion accidents, and the optimal diameter range used by the water fog, but also provide experimental reference for the numerical simulation of hydrogen/air explosion suppression in semi-open space, and promote the development of hydrogen explosion suppression theory. In terms of engineering applications, this study can provide a theoretical basis for the layout of fire fighting equipment in the engine room of nuclear power plants or hydrogen-powered ships.     

In situ 2D mapping of hydrogen entry into an Fe sheet under a droplet of NaCl solution using a hydrogenochromic sensor

The distribution of hydrogen entering an Fe sheet under a droplet of NaCl solution was successfully visualized using a hydrogenochromic sensor consisting of a polyaniline layer and a Ni intermediate layer. At the initial stage of corrosion, the hydrogen entry was barely confirmed. The hydrogen entry was observed as the corrosion proceeded, and the preferential hydrogen entry site corresponded to the rust-formed area. It was postulated that the hydrogen entry is promoted by the decrease in pH due to the hydrolysis reactions of Fe ions under the rust. The hydrogenochromic sensor paves the way for the visualization of the hydrogen entry into metals under corrosion conditions.