On the Catalytic Mechanism of 3d and 4d Transition-Metal-Based Materials on the Hydrogen Sorption Properties of Mg/MgH2

The slow hydrogenation/dehydrogenation kinetics and high thermodynamic stability of the Mg–H bond are the two major limitations for the large-scale utilization of MgH2. In this review, we introduce the catalytic mechanism of 3d and 4d transition metal (TM) on the hydrogen sorption properties of Mg/MgH2. The relative contribution of interatomic interactions to the thermodynamic stability of the TM-substituted MgH2 system is discussed. A synergy effect between the electronegativity and the radius of the TM element is proposed to explain the charge transfer process between TM and H in the TM-substituted MgH2 system. The catalytic mechanism of TM nearby the surface of Mg is more complicated than that in the volume of Mg, as the surface-doped TM can experience more options for doping sites, leading to the hindrance effect and causing various contributions of the d band center to the dissociation of hydrogen molecules and the diffusion of hydrogen atoms nearby the surface of Mg. In terms of the catalytic mechanism of TM for hydrogen sorption kinetics of Mg/MgH2, we particularly focused on the “hydrogen pump” effect existing in the Mg–TM–H system. Other mechanisms, such as a possible catalytic mechanism of TM for the hydrogen sorption properties of nano-sized freestanding Mg/MgH2, were also presented.

Experimentally Observed Nucleation and Growth Behavior of Mg/MgH2 during De/Hydrogenation of MgH2/Mg: A Review

With the increasing energy crisis and environmental problems, there is an urgent need to seek an efficient renewable energy source, and hydrogen energy is considered one of the most promising energy carriers. Magnesium is considered a promising hydrogen storage material due to its high hydrogen storage density, abundant resources, and low cost. However, sluggish kinetic performance is one of the bottlenecks hindering its practical application. The kinetic process of hydrogenation/dehydrogenation can be influenced by both external and internal factors, including temperature, pressure, elementary composition, particle size, particle surface states, irregularities in particle structure, and hydrogen diffusion coefficient. The kinetic performance of the MgH₂/Mg system can be effectively improved by more active sites and nucleation centers for hydrogen absorption and desorption. Herein, we briefly review and discuss the experimentally observed nucleation and growth behavior of Mg/MgH₂ during de/hydrogenation of MgH₂/Mg. In particular, the nucleation and growth behavior of MgH₂ during the hydrogenation of Mg is discussed from the aspect of temperature and hydrogen pressure.

Materials Research Directions Toward a Green Hydrogen Economy: A Review

A constellation of technologies has been researched with an eye toward enabling a hydrogen economy. Within the research fields of hydrogen production, storage, and utilization in fuel cells, various classes of materials have been developed that target higher efficiencies and utility. This Review examines recent progress in these research fields from the years 2011-2021, exploring the most commonly occurring concepts and the materials directions important to each field. Particular attention has been given to catalyst materials that enable the green production of hydrogen from water, chemical and physical storage systems, and materials used in technical capacities within fuel cells. The quantification of publication and materials trends provides a picture of the current state of development within each node of the hydrogen economy.

Convergence of Electronic Structure Properties in Ionic Oxides Within a Fragment Approach

Embedded-cluster models of crystalline solids are important to allow accurate wave function methods to be applicable to solids. The ab-initio model potential method, in which the crystal is divided into three different fragments, one quantum fragment, one ab-initio model potential fragment and one point-charge fragment, has historically been shown to be a viable tool for describing the electronic structure in ionic solids. The optimal size of these regions is, of course, individual for each crystal. In this study we analyzed the convergence of the electronic structure properties with respect to an increase of the size of the quantum part and the layer of potentials. MgO crystal and Ni: MgO were used for this purpose as examples of an ideal crystal and a crystal with a point defect. We demonstrated that with an increase of the cluster size, the electron density in the inner part of the cluster becomes very similar to the electron density in the periodic model. Clusters, embedded into a layer of model potential and electrostatic field, are a good alternative to periodic description.

Reactivity of Coinage Metal Hydrides for the Production of H2 Molecules

The formation of molecular hydrogen as well as the possibility of using coinage metal hydrides as a prospective complex to produce hydrogen was presented in this work. Therefore, the reactions involving the interaction between two coinage metal hydrides, MH (M=Cu, Ag and Au, homo and heterodimers), were studied. The free energy profiles corresponding to aforementioned complexation were analysed by means of ab initio methods of quantum chemistry. The characteristics of these intermediates, final complexes and the electron density properties of the established interactions were discussed.

Structure–property relationship of novel supramolecular gels based on coumarins

LMWGs based on coumarins could form supramolecular gels with unusual mechanical properties explained by its interactions at theoretical level.

Computational and Experimental 1H-NMR Study of Hydrated Mg-Based Minerals

Magnesium oxide (MgO) can convert to different magnesium-containing compounds depending on exposure and environmental conditions. Many MgO-based phases contain hydrated species allowing ¹H-nuclear magnetic resonance (NMR) spectroscopy to be used in the characterization and quantification of proton-containing phases; however, surprisingly limited examples have been reported. Here, ¹H-magic angle spinning (MAS) NMR spectra of select Mg-based minerals are presented and assigned. These experimental results are combined with computational NMR density functional theory (DFT) periodic calculations to calibrate the predicted chemical shielding results. This correlation is then used to predict the NMR shielding for a series of different MgO hydroxide, magnesium chloride hydrate, magnesium perchlorate, and magnesium cement compounds to aid in the future assignment of ¹H-NMR spectra for complex Mg phases.