Surface Adsorption Of Hydrogen Research Articles

Hydrogen Production, Purification, Storage, Transportation, and Their Applications: A Review

The world is looking for clean and green energy as substitution for fossil fuels to minimize the greenhouse effect and climate changes threatening our existence. Solar energy, wind energy, and hydrogen gas‐based energy are few examples of promising sources of energy alternatives to fossil fuels. Hydrogen gas‐based energy is in focus today due to its availability in plenty of combined forms such as water, hydrocarbons, natural gases, etc. However, its storage and transportation are major challenges due to the low volumetric density and explosive nature of hydrogen. The scientific community is in search of suitable, economically viable, and energy‐efficient storage systems and transportation of hydrogen gas. Based on numerous studies, surface adsorption of hydrogen by high surface area nanoporous solids such as carbon and metal–organic framework (MOF)‐based nanofiber materials are most suitable for storage applications. Electrospinning process provides a gateway for the preparation of lightweight, highly porous nanofibers for efficient hydrogen adsorption. Herein, the production and use of electrospun polymer nanofibers and MOFs for the storage and transportation of hydrogen are presented.

Critical role of hydrogen sorption kinetics in electrocatalytic CO2 reduction revealed by on-chip in situ transport investigations

Precise understanding of interfacial metal−hydrogen interactions, especially under in operando conditions, is crucial to advancing the application of metal catalysts in clean energy technologies. To this end, while Pd-based catalysts are widely utilized for electrochemical hydrogen production and hydrogenation, the interaction of Pd with hydrogen during active electrochemical processes is complex, distinct from most other metals, and yet to be clarified. In this report, the hydrogen surface adsorption and sub-surface absorption (phase transition) features of Pd and its alloy nanocatalysts are identified and quantified under operando electrocatalytic conditions via on-chip electrical transport measurements, and the competitive relationship between electrochemical carbon dioxide reduction (CO2RR) and hydrogen sorption kinetics is investigated. Systematic dynamic and steady-state evaluations reveal the key impacts of local electrolyte environment (such as proton donors with different pKa) on the hydrogen sorption kinetics during CO2RR, which offer additional insights into the electrochemical interfaces and optimization of the catalytic systems.

A DFT analysis unravelling hydrogen sorption pathways in Laves phase Cu2Cd

A comprehensive study to establish sorption pathways for molecular and atomic hydrogen in Cu2Cd Laves phase by means of density functional theory calculations is reported. The surface energy of Cu2Cd was calculated exposing the (0001) surface with two different planes, one being Cu terminated while the other being Cu-Cd terminated. Both were discerned to have comparable surface energies. Adsorption sites for the relevant molecular and atomic hydrogen were identified on both the planes and the associated energetics were determined. Adsorption of atomic hydrogen was found to be energetically favoured when compared to the molecular adsorption of hydrogen. Diffusion pathways for atomic hydrogen from the surface to the bulk were investigated. The study provides detailed insights into the identification and energetics of the surface adsorption of hydrogen, and its diffusion to the subsurface sites, thus unravelling the sorption pathways in Cu2Cd Laves phase for potential hydridic storage of hydrogen.

Hydrogen storage in TiVCrMo and TiZrNbHf multiprinciple-element alloys and their catalytic effect upon hydrogen storage in Mg

Hydrogen storage performance of nearly equimolar alloys TiVCrMo and TiZrNbH (HEA's) was studied. The alloys were prepared by repeated arc-melting in the form of single-phase alloys and as their multi-phase analogues prepared either by high-energy ball milling (HEBM) of the arc-melted ingots or by HEBM of pure elements. Besides these four-component experimental materials, also their mixtures with Mg were investigated that were prepared by HEBM with Mg (composition in both cases was Mg – 10 wt % HEA). Hydrogen sorption experiments were carried out in temperature interval between 240 °C and 380 °C under hydrogen-gas pressure up to 50 bars. Kinetic curves, temperature-programmed desorption spectra and concentration-pressure isotherms were measured. It was found that activation energy of hydrogen desorption, |Ea|, for materials with Mg was significantly decreased compared to pure Mg. Hydride formation enthalpy, ΔH, observed for all the materials under study was about the same as that for pure MgH2. Hydrogen absorption capacity in pure four-component HEA's was negligible; only hydrogen surface adsorption was detected. The capacity of mixtures of HEA's with Mg was between 3.5 and 6 wt % H2.

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.

Chemisorption, diffusion and permeation of hydrogen isotopes in bcc bulk cr and cr(100) surface: First-principles dft simulations

Chromium, a transition metal, is one of the important constituents, used widely in steel. It is of paramount importance to study the behavior of hydrogen isotopes with Cr to design a suitable barrier materials for arresting the permeation of H isotopes. Here, the interaction and dynamical behaviours of hydrogen isotopes in bcc Cr lattice have been studied employing plane wave based density functional theory. Nudge elastic band methods have been used to determine the activation energy barrier whereas phonon calculations are performed to calculate the zero point energy in order to investigate the isotope effects. The dissociative surface adsorption of hydrogen is predicted to be exothermic, whereas surface to sub-surface and bulk absorption is found to be endothermic but the vacancy induced absorption energy for H atom in bulk Cr has been found to be exothermic. The diffusion of H atom from one tetrahedral hole to the adjacent tetrahedral hole has been established to be the most favoured pathway. The lighter H atom was shown to have higher diffusion coefficients, permeability coefficients, solubility and rate constants than heavier D and T atoms. The computed values of diffusion, permeability and solubility of H in Cr follow the experimental prediction. The computed results presented here might be of assistance in the future design of suitable materials to arrest the permeation of tritium.

Control of YH3 formation and stability via hydrogen surface adsorption and desorption

Yttrium is known to form two hydrides: YH2, a metal, and YH3, which is dielectric. However, the stability of YH3 is not fully understood, especially in the context of thin films, where the yttrium layer must be coated to protect it from oxidation. In this work, we show that the stability of a YH3 thin film depends on the capping layer material. Our investigation reveals that YH3 appears to be stabilized by hydrogen that is adsorbed to the capping layer surface. This is evidenced by the YH3-YH2 transition temperature, which was found to be correlated with the desorption temperature of hydrogen from the surface. We posit that surface-adsorbed hydrogen prevents hydrogen from diffusing out of the thin film, which limits YH3 dissociation to the solubility of hydrogen in the YH2/YH3 thin film.

Interlayer Carbon Bond Formation Induced by Hydrogen Adsorption in Few-Layer Supported Graphene

We report on the hydrogen adsorption induced phase transition of a few layer graphene (1 to 4 layers) to a diamondlike structure on Pt(111) based on core level x-ray spectroscopy, temperature programed desorption, infrared spectroscopy, and density functional theory total energy calculations. The surface adsorption of hydrogen induces a hybridization change of carbon from the sp2 to the sp3 bond symmetry, which propagates through the graphene layers, resulting in interlayer carbon bond formation. The structure is stabilized through the termination of interfacial sp3 carbon atoms by the substrate. The structural transformation occurs as a consequence of high adsorption energy.

Concentration-dependent hydrogen diffusion in hydrogenation and dehydrogenation of vanadium-coated magnesium nanoblades

We carry out a computational investigation to show how the exponential concentration dependence of hydrogen diffusion, which was recently verified in a combined experimental and analytical study, could affect the characteristics of hydrogenation and dehydrogenation of a vanadium-coated magnesium nanoblade. A reaction model is built that separates hydrogen surface sorption and interior diffusion during the hydrogenation/dehydrogenation process. For the hydrogenation process, the hydrogen surface adsorption is much faster than the hydrogen diffusion, resulting in high hydrogen concentration buildup at the surface at a relatively low temperature. With increasing temperature, the hydrogen diffusion time decreases more rapidly than the hydrogen surface adsorption time. This leads to a relatively low-gradient diffusion field in the nanoblade during most time of the hydrogenation process, and no shell–core structure with a finite hydride layer is observed. However, for the dehydrogenation process, when hydrogen molecules are released at the surface, a hydride core is formed inside the nanoblade and the interface recedes gradually. The receding rate of the hydride core is determined by the hydrogen molecule release rate. In a two-dimensional simulation with decorated vanadium catalyst islands on the surface, isolated interior hydride islands are sometimes observed before the hydride core entirely fades away. The hydride core boundary is sharper at lower temperature when the surface reaction rate is high relative to the interior diffusion rate.

Hydrogen trapping in martensitic steel investigated using electrochemical permeation and thermal desorption spectroscopy

Hydrogen embrittlement (HE) is caused by a hydrogen surface adsorption followed by absorption and the hydrogen diffusion/trapping phenomenon. Hydrogen entry in metal needs accurate measurements to improve HE models. In this context, hydrogen trapping energy and irreversibly trapped hydrogen concentration are determined on a quenched and tempered martensitic steel using an electrochemical permeation technique and thermal desorption spectroscopy. A comparison between both techniques is carried out: a good accordance of experimental results was obtained considering trapped hydrogen concentration and trapping energy values.

Hydrogen absorption in palladium films sensed by changes in their resistivity

The resistance of pure palladium films of 11, 30 and 54 nm thickness was monitored during their exposure to H2 at pressures ranging between 1 and 20 Torr. After completing a cycle of H2 absorption/desorption, the resistivity changed in a ``saw tooth'' fashion similar to the changes observed in surface adsorption of hydrogen by other transition metals. Large resistance changes are observed in these studies, confirming that bulk hydrogen absorption occurs in Pd while hydrogen surface adsorption becomes dominant over bulk absorption in other metals such as niobium. The resistance change curves carry the information of the kinetics of absorption.

Structural changes induced by hydrogen absorption in palladium and palladium–ruthenium alloys

The structural changes in Pd and Pd–Ru alloys induced by the repeated absorption–desorption of hydrogen have been studied. It is found that absorption–desorption cycles produce structural changes in Pd whereas the addition of small amounts of Ru inhibits these hydrogen-induced changes. The experimental results show that bulk hydrogen absorption occurs in Pd, while hydrogen surface adsorption becomes dominant over bulk absorption, in the Pd–Ru alloy.

Hydrogen adsorption of the [0 0 1] diamond surface

A slab model employing a tight binding scheme is used to study changes in the electronic structure of hydrogen on a [0 0 1] diamond surface. We suggest that the valence band tailing observed in photoemission studies of the [1 1 1] surface reflects a range of atomic relaxations due to the presence of hydrogen which in turn effects the dispersion of the surface defect levels throughout the band structure. Electronic structure well into the bulk is affected by the surface adsorption of hydrogen and is far different from that of the perfect surface.