Generation of excited electronic states at the nonmetal surface by the hydrogen atoms beam

The low energy excitation electronic states by the hydrogen atoms at the nonmetal surface are described using several possible mechanisms. The study results of the luminescence excited surface of the phosphor ZnS-Tm during interaction with H atoms are reported. Nonstationary with time the light intensity from ZnS-Tm is detected. This phenomenon interpreted on basis of the exchange-associative mechanism taking into account the acceleration of the surface recombination of hydrogen atoms in the adsorbed layer of the vibrationally excited hydrogen molecules. The rates of the absorption and recombination of hydrogen atoms and the desorption rate of the hydrogen molecules are defined. The possible mechanisms of excitation of the surface electronic states during interaction with the hydrogen low-energy atoms are discussed.     

Application of atomic simulation for studying hydrogen embrittlement phenomena and mechanism in iron-based alloys

High-strength iron-based alloys serving in hydrogen-containing environments often faces a critical problem of hydrogen embrittlement, which involves intricate mechanisms across multiple lengths and time scales resulting in catastrophic consequences. It is challenging to track the evolution or/and nanoscale distribution of hydrogen atoms via experiments directly, whereas atomic simulation displays its great advantages in revealing the hydrogen-related behaviors and interaction mechanism. Most studies on hydrogen embrittlement mechanisms via atomic simulations focused on iron, as it is the matrix composition of steel. Herein, we summarize recent advances about applying atomic simulations, including density functional theory and molecular dynamics, in understanding the interaction between hydrogen atoms and various defects in iron-based alloys. Finally, some scientific issues and challenges in this field are discussed to provide insight for future researches.     

Influence of the Fe-doping on hydrogen behavior on the ZrCo surface

Ab initio calculations have been carried out to investigate the adsorption, dissociation, and diffusion of atomic and molecular hydrogen on the Fe-doped ZrCo (110) surface. It is found that the adsorption of H₂ on doped surface seems thermodynamically more stable with more negative adsorption energy than that on the pure surface, and the dissociation energy of H₂ on doped surface is much bigger therefore. However, compared with the pure system, there are fewer adsorption sites for spontaneous dissociation. After dissociation, the higher hydrogen adsorption strength sites would promote the H atom diffusion towards them where they can permeate into the bulk further. Furthermore, the ZrCo (110) surface possesses much higher hydrogen permeability and lower hydrogen diffusivity than its corresponding ZrCo bulk. Moreover, further comparison of the present results to analogous calculations for pure surface reveals that the Fe dopant facilitates the H₂ molecule dissociation. Unfortunately, this does not improve the hydrogen storage performance of ZrCo alloy due to the H atom diffusion on the surface and into bulk are prevented with higher reaction energetic barriers by doping Fe. Consequently, ZrCo (110) surface modified with Fe atoms should not be preferred as a result of its terrible hydrogen permeability. A clear and deep comprehending of the inhibiting effect of Fe dopant on the hydrogen storage of ZrCo materials from the perspective of the surface adsorption of hydrogen are obtained from the present results.     

Micro-mechanism study on the effect of O2 poisoned ZrCo surface on hydrogen absorption performance

Hydrogen storage alloys are usually susceptible to poisoning by O₂, CO, CO₂, etc., which decreases the hydrogen storage property sharply. In this paper, the adsorption characteristics of oxygen on the ZrCo(110) surface were investigated, and the effect of oxygen occupying an active site on the surface on the hydrogen adsorption behavior was discussed. The results show that the dissociation barrier of H₂ is increased by more than 26% after O occupies the active sites on the ZrCo(110) surface, and the probability of H₂ adsorption and dissociation decreases significantly. The adsorption energy of H atoms on the O–ZrCo(110) surface decreased by 18–56%, and the adsorption stability of H decreased. In addition, H atom diffusion on the surface and into bulk are prevented with higher reaction energetic barriers by O occupying active sites. Eventually, the ability of the ZrCo surface to adsorb hydrogen is seriously reduced.     

Extending the detection range and response of TiO2 based hydrogen sensors by surface defect engineering

With the increasing usage of hydrogen energy, the requirements for hydrogen detection technology is increasingly crucial. In addition to bringing down the working temperature, further improvement in the response and broadening the detection range of hydrogen sensors in particular are still needed. TiO₂ based sensors show great promise due to their stable physical and chemical properties as well as low cost and easy fabrication, but their detection range and low concentration response requires further improvement for practical applications. Here (002) oriented rutile TiO₂ thin films are prepared by a hydrothermal method followed by annealing in either air, oxygen, vacuum or H₂ and the hydrogen sensing performance are evaluated. Raman results show that TiO₂ thin films annealed in vacuum and hydrogen have more oxygen vacancies, while those annealed in air and oxygen have a more stoichiometric surface. Annealing in an oxygen-rich atmosphere is shown to extend the detection range of the TiO₂ sensors while annealing in anaerobic atmospheres increases their response. At high hydrogen concentrations surface adsorbed O₂⁻ is the dominant factor, while at low concentrations the Schottky barrier between Pt and TiO₂ is key to achieving a high response. Here we show controlling the TiO₂ surface properties is essential for optimizing hydrogen detection over specific concentration ranges. We demonstrate that adjusting the annealing conditions and ambient provides a simple method for tuning the performance of room temperature operating TiO₂ based hydrogen sensors.     

High density hydrogen storage in nanocavities: Role of the electrostatic interaction

High pressure H₂ adsorption isotherms at N₂ liquid temperature were recorded for the series of cubic nitroprussides, Ni_1−xCo_x[Fe(CN)₅NO] with x = 0, 0.5, 0.7, 1. The obtained data were interpreted according to the effective polarizing power for the metal found at the surface of the cavity. The cavity volume where the hydrogen molecules are accumulated was estimated from the amount of water molecules that are occupying that available space in the as-synthesized solids considering a water density of 1 g/cm³. The calculated cavity volume was then used to obtain the density of H₂ storage in the cavity. For the Ni-containing material the highest storage density was obtained, in a cavity volume of 448.5 Å³ up to 10.4 hydrogen molecules are accumulated, for a local density of 77.6 g/L, above the density value corresponding to liquid hydrogen (71 g/L). Such high value of local density was interpreted as related to the electrostatic contribution to the adsorption potential for the hydrogen molecule within the cavity.     

The use of ultrapure molecular hydrogen enriched with atomic hydrogen in apparatuses of artificial lung ventilation in the fight against virus COVID-19

COVID-19 is a disease caused by the SARS-CoV virus. It stands for severe acute respiratory syndrome, which affects the lungs.The process of replication and progression of the COVID-19 virus causes the formation of an excessive amount of reactive oxygen species and inflammation.Many studies have been carried out that have demonstrated that hydrogen has strong anti-inflammatory properties. It reduces hypotension and other symptoms by reducing inflammation and oxidative stress.Oxygen mixture, enriched with Hydrogen, - helps to reduce the resistance of the respiratory tract and frees up access to the pulmonary alveolus, which improves the penetration of oxygen into the lungs. Since hydrogen is an antioxidant, it helps to reduce the burden on the immune system, helps to maintain the body's health and its ability to quickly recover.When electrolysers are used to produce an oxygen-hydrogen mixture, alkaline mist and other impurities can enter the patient's lungs and cause poisoning and chemical burns.For this reason, the use of atomic hydrogen obtained from metal hydride sources for ventilation of the lungs will be more effective for treating COVID-19 than a molecular hydrogen-oxygen mixture from an electrolyzer.A functional diagram of a metal hydride source of atomic hydrogen to an artificial lung ventilator is shown. It is possible to create a series of hydrogen storage tanks of various capacities.     

Comparative study of the hydrogen isotopes yield from Ti,Zr, Ni,Pd, Pt during thermal,electric current and radiation heating

The results of studying the hydrogen isotopes (H, D) yield of Ni, Pd, Pt, Ti, Zr metals with linear heating: a) by the accelerated electrons beam with energy up to 35 KeV, b) by joule heat of AC (50 Hz) through samples, c) by external coaxial furnace samples in metal (stainless steel) and d) quartz vacuum cells are presented. The highest temperature of the position of the maximum intensity hydrogen isotopes release at the linear heating corresponds to the samples heating in a metal vacuum cell, an external coaxial furnace. The lowest temperature position of the maximum intensity hydrogen isotopes release corresponds to the heating by accelerated electrons beam. The difference in these positions of the maximum is ΔТ ≈ 350°С. Difference in maxima position of the hydrogen and deuterium release into the low-temperature region is significant (ΔТ ≈ 50–100°С) for the Ni, Pd, Pt samples, and insignificant (ΔТ <10°С) for the Ti and Zr samples was found, when metals are heated by electric current or in a quartz vacuum cell compared to their heating in a metal vacuum cell.Possible mechanisms of non-equilibrium stimulation of the hydrogen isotopes release from metals, due to the accumulation of external energy by the hydrogen subsystem of crystals considered theoretically. The notions used wherein are in agreement with the obtained experimental results.     

Low-index surface investigation of KAlH4: Theoretical attempt to study the surface effect on the hydrogen storage properties

Different preparations of complex hydrides lead to different hydrogen uptake and release. Besides, Potassium Aluminum hydride is a structure with different re/dehydrogenation properties than the rest of alanates. Given these considerations, we investigated nine stable cleavages on the (100), (010), (001), (111), and (101)KAlH₄ surfaces. The results reveal that, while the (010) surface energy is much higher, all the other surfaces are approximately in the same range of energy. Some of these surfaces would be placed on top of the nanocrystallites and the different decomposition pathways may be originated from the different characteristics of these surfaces, which is one of the central issues of the present study. Our results are in accordance with experimental data indicating that long hours milling of alanates just creates fresh surfaces and the structures remain unchanged. Due to the surface effect, huge changes in electronic and geometric characteristics occur. The band gaps are narrowed up to 2eV, which alongside with massive changes in chemical bonds, lead to an improved dehydrogenation relative to the bulk.     

Investigation of surface interaction in rGO-CdS photocatalyst for hydrogen production: An insight from XPS studies

Formation of heterojunction in supported-photocatalyst plays an important role in photocatalysis for hydrogen production. However, study of this formation is needed to be more. Reduced graphene supported-cum-doped Cadmium sulphide (rGO-CdS) is widely employed for the production of hydrogen by photocatalysis splitting of water. The Formation of surface interaction between rGO and CdS was explained by detailed analysis by using x-ray photoelectron spectroscopy with depth profiling, Fourier-transform infrared spectroscopy and electrochemical impedance spectroscopy. The charge transfer phenomena through heterojunction are also explicated. The higher conductivity of rGO further facilitated the transmission of electrons to the interface of solid-liquid. Thus, the restriction of charge recombination and greater mobility of electron yielded superior activity to the CdS/rGO catalyst which was prepared by impregnation method followed by the H₂S gas reaction with high temperature.     

Models,methods and approaches for the planning and design of the future hydrogen supply chain

The infrastructure of hydrogen presents many challenges and defies that need to be overcome for a successful transition to a future hydrogen economy. These challenges are mainly due to the existence of many technological options for the production, storage, transportation and end users. Given this main reason, it is essential to understand and analyze the hydrogen supply chain (HSC) in advance, in order to detect the important factors that may play increasing role in obtaining the optimal configuration. The objective of this paper is to review the current state of the available approaches for the planning and modeling of the hydrogen infrastructure. The decision support systems for the HSC may vary from paper to paper. In this paper, a classification of models and approaches has been done, and which includes mathematical optimization methods, decision support system based on geographic information system (GIS) and assessment plans to a better transition to HSC. The paper also highlights future challenges for the introduction of hydrogen. Overcoming these challenges may solve problems related to the transition to the future hydrogen economy.     

High hydrogen storage ability of a decorated g-C3N4 monolayer decorated with both Mg and Li: A density functional theory (DFT) study

In this work, the hydrogen storage properties of a g-C₃N₄ monolayer decorated with both Mg and Li were thoroughly investigated by performing density functional theory (DFT) calculations. Along these lines, the projected densities of states (PDOS) and the Bader Charge analysis showed that both Mg and Li atoms can transfer their electronic charges to the g-C₃N₄ monolayer. Interestingly, the latter is transformed from a semiconductor material to a metallic conductor configuration, while a local electric field is formed around it. On top of that, the formed local electric field polarized hydrogen molecules and as a result, led to an enhanced hydrogen adsorption ability. Mg atoms have more outmost electrons, and more charges can be transferred to the monolayer, which leads to the creation of a stronger local electric field to adsorb an elevated number of hydrogen molecules than Li atoms. On the other hand, Li atoms are lighter, more active and easier to lose outmost electrons than Mg atoms. By considering these advantages, a g-C₃N₄ monolayer decorated with one unit of both Mg and Li was investigated, which has the ability to adsorb 10 hydrogen molecules, leading thus to a high hydrogen storage capacity of 10.01 wt %. Our work paves the way for the development of novel material configurations for improved hydrogen storage applications.     

Design of advanced self-supported electrode by surface modification of copper foam with transition metals for efficient hydrogen evolution reaction

Electrocatalytic water splitting is one of the most favorable methods for industrial-scale hydrogen production, but high cost and scarcity of commercially available noble metals restrict its application for hydrogen evolution reaction (HER). It is challenging to develop efficient non-noble metal-based electrocatalysts for HER. Herein, a Ni–Cr was doped on Copper foam (CF) substrate by adopting a simple annealing process. The high electrocatalytic efficiency for HER was achieved with Ni–Cr@CF electrode in strong basic medium with a lower overpotential of 144 mV to gain a current density of 10 mA cm⁻² with a small Tafel slope of 88 mV dec⁻¹. After surface modification, the CF substrate exhibits that the entire surface was uniformly covered with Ni–Cr species ensuring the fast reaction kinetics due to the efficient electron transfer process between the substrate and active catalyst. Moreover, the Ni–Cr@CF electrode exhibits excellent stability up to 2000 cycles under the strong basic medium.     

The advantage of using in-situ methods for studying hydrogen mass transport: Neutron radiography vs. carrier gas hot extraction

Neutron radiography (NR) is compared with the commonly used carrier gas hot extraction (CGHE) technique. We performed isothermal hydrogen effusion experiments at 623 K to study the mass transport kinetics. The investigated material was technical iron. The quantification of the hydrogen mass flow is done for NR by using concentration standards. The temporal hydrogen concentration evolution in the sample coincides well for both methods, i.e. NR and CGHE, and is in good agreement with literature. The advantages of the NR method are the non-destructive nature of measuring and the in-situ determination of hydrogen concentrations with high spatial and temporal resolution. Remaining hydrogen inside the sample can be identified directly by the NR method.     

Evaluation of the hydrogen adsorption onto Li and Li+ decorated circumtrindene (C36H12): A theoretical study

Circumtrindene as a π-bowl shaped carbon structure decorated by Li and Li⁺ and examined for H₂ adsorption using M06-2X/6-311++G(d,p)//B3LYP/GEN level of theory. All polygons, bonds and various carbon types, in concave and convex sides, were examined to find the best location for Li and Li⁺. ZPE and BSSE-corrected interaction energy values were calculated for connection of Li or Li⁺ to circumtrindene and for connection of H₂ to LiC₃₆H₁₂ or Li⁺-C₃₆H₁₂. Better understanding of the adsorption properties were achieved by DOS, PDOS, OPDOS diagrams and NBO analysis. Results showed that in LiC₃₆H₁₂ and Li⁺-C₃₆H₁₂ complexes, the concave side has more binding energy than the convex ones and Li⁺-C₃₆H₁₂ has more binding energy than LiC₃₆H₁₂. Also, for LiC₃₆H₁₂, when Li was in center polygon and concave side and for Li⁺-C₃₆H₁₂, when Li⁺ was in 6-2 polygon and convex side, the highest interaction energy were obtained. For H₂ adsorption, the complexes contain Li and Li⁺ in center polygon and concave face have the highest binding energy, equal to 15.72 and 16.29 kcal mol^?1, respectively. Binding energy values indicated that adsorption of Li or Li⁺ onto C₃₆H₁₂ and adsorption of H₂ onto LiC₃₆H₁₂ or Li⁺-C₃₆H₁₂ in all positions are chemisorptions, but the connections are not so strong for H₂ molecules.     

Role of extraframework metal sites for hydrogen adsorption into the pores of a zeolite: FT-IR study

In order to compare the adsorptive properties of nanoporous zeolites containing extraframework cations of different nature, we have studied the interaction of H₂ with Na-A, Ca-A, and Co,Na-A zeolites. Low temperature Fourier transform infrared (FT-IR) spectroscopy was used for the investigation, as this technique is highly sensitive and responsive to the nature of the gas/surface interaction and can in addition allow for the estimation of the adsorption enthalpy. In all cases the spectra of adsorbed H₂ have complex structure due to ortho/para splitting as well as to surface structural disorder. Na⁺ and divalent Ca²⁺ were found to induce almost similar perturbation on H₂ molecule, resulting in the shift of the H-H vibrational frequency of −86 cm⁻¹ and −76 cm⁻¹ respectively (as compared to the Raman frequency of gaseous H₂). The enthalpy of adsorption, estimated by the Variable Temperature Infrared (VTIR) method, is −13 ± 1 kJ mol⁻¹ for the strongest adsorptive sites in Na-A and Ca-A samples. In the case of Co,Na-A the shift of the H-H frequency due to the formation of H₂?Co²⁺ complexes is larger (ca. −180 cm⁻¹) suggesting that the interaction can involve some, although small, chemical contribution.     

Mg3Cd: A model alloy for studying the destabilization of magnesium hydride

We prepared an ordered Mg₃Cd alloy by high energy ball milling of elemental powders. The synthesized alloy exhibited good hydrogenation kinetics and reversibly absorbed about 2.8 wt. % of hydrogen. The temperature dependence of hydrogenation kinetics of the alloy measured in the range of temperatures covering the order-disorder phase transformations in the Mg₃Cd and MgCd phases did not exhibit any anomalies and could be fitted with a single Arrhenius line. The measured apparent activation energy (69 ± 2 kJ/mol) hinted that hydrogenation process was controlled by diffusion of Cd in metallic phase. The pressure-composition isotherms exhibited negligible pressure hysteresis and sloping pressure plateau. Based on microstructural evidence obtained with the aid of X-ray diffraction and scanning electron microscopy, we built a thermodynamic model predicting the plateau hydrogen pressure for partially hydrogenated alloy. The predictions of the model were in a good agreement with the experimental data. Finally, we discussed the origins and the growth mechanisms of Cd whiskers observed in the alloys after full hydrogenation cycle.     

Ni supported on La2O3+ZrO2 for dry reforming of methane: The impact of surface adsorbed oxygen species

This research investigates the effect of doping Ni/La₂O₃+ZrO₂ with nitrates of Ca, Cr, Ga, and Gd on the conversion of the feed and H₂/CO molar ratio. The development of these catalysts is intended to tackle inefficiency of dry reforming of CH₄ which stems from deactivation and sintering of active metal. All promoted catalysts perform better than the un-promoted catalyst. Cr promoted sample gives the best performance with CH₄ and CO₂ conversion averaging 83 and 88% respectively. Also, it maintains good stability. The relative ease of reducing the catalyst plus its porous nature are responsible for its performance. Ca promoted sample has the same area as that of the support indicating the movement of Ni–Ca out of the pores of the support during calcination. According to thermogravimetric analysis, the un-promoted catalyst records the highest amount of carbon while the Ca promoted sample has about 18%.     

Manipulating photocatalytic pathway and activity of ternary Cu2O/(001)TiO2@Ti3C2Tx catalysts for H2 evolution: Effect of surface coverage

A Cu₂O/(001)TiO₂@Ti₃C₂T_x photocatalyst was synthesized via a wet-chemistry reduction method by N, N-dimethylformamide (DMF). By scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), it was revealed that the surface coverage of photocatalyst increased with the loading amount of Cu₂O, while the particle size of Cu₂O did not change significantly. The photocatalytic activity and mechanism of ternary Cu₂O/(001)TiO₂@Ti₃C₂T_x photocatalyst heavily depend on the surface coverage of copper species. When the surface coverage of photocatalyst by Cu₂O was low, the Ti₃C₂T_x acted as hole reservoir. Cu₂O was firstly reduced in situ to metallic copper by excited electrons. Then the reverse movement of carriers enabled the spatial separation of photogenerated electron-hole pairs, and afforded relatively high hydrogen evolution (more than 1100 μmol h⁻¹ (g CuO_x TiO₂)⁻¹). When the coverage of Cu₂O on (001)TiO₂@Ti₃C₂T_x was too high at high loading amounts, Ti₃C₂T_x failed to play the role of hole trapping. Under that circumstance, the photocatalytic reaction follows p-n junction mechanism, leading to low hydrogen productivity. The results here shed light on the relationship between structure and activity of Cu₂O/(001)TiO₂@Ti₃C₂T_x, which was conducive to the development of the MXene-based photocatalysts.     

Could one non-noble metal surface with non-noble substrate be a good hydrogen evolution catalyst: Performance of transition metal A monolayer on B substrate in theory frame

Could materials only including non-noble metals be good HER catalysts? To deal with this puzzle, computational screening of 132 different non-noble transition metal A/B surfaces for HER (A monolayer on B), are carried out by first-principles calculations systematically. The formation energies and dissolution potentials are calculated to access stabilities of A/B in vacuum and in solution, respectively. The realistic catalytic surfaces with oxygen or hydroxyl (co)adsorption are confirmed by analyzing Surface Pourbaix diagrams. Finally, three A/B surfaces (Cu/Mo, Mo/W, and Ti/Nb) with high stabilities and high HER exchange current densities (8.51, 3.39, 2.83 mA/cm²) are screened out. Further electronic properties analysis reveals that the different interactions between H 1s and d orbital, s orbital of A atoms will determine the feasible application of d and s band centers to uncover water effect and substrate effect on hydrogen adsorption ability, and tune the HER activity of A/B in the end.