RESUMEN
The efficient operation of a metal hydride reactor depends on the hydrogen sorption and desorption reaction rate. In this regard, special attention is paid to heat management solutions when designing metal hydride hydrogen storage systems. One of the effective solutions for improving the heat and mass transfer effect in metal hydride beds is the use of heat exchangers. The design of modern cylindrical-shaped reactors makes it possible to optimize the number of heat exchange elements, design of fins and cooling tubes, filter arrangement and geometrical distribution of metal hydride bed elements. Thus, the development of a metal hydride reactor design with optimal weight and size characteristics, taking into account the efficiency of heat transfer and metal hydride bed design, is the relevant task. This paper discusses the influence of different configurations of heat exchangers and metal hydride bed for modern solid-state hydrogen storage systems. The main advantages and disadvantages of various configurations are considered in terms of heat transfer as well as weight and size characteristics. A comparative analysis of the heat exchangers, fins and other solutions efficiency has been performed, which makes it possible to summarize and facilitate the choice of the reactor configuration in the future.
RESUMEN
In this paper, we study the influence of hydrogen concentration on the binding energies in magnesium hydrides. The impact of aluminum atom addition on the hydrogenation behavior of magnesium was theoretically and experimentally defined. Doping Al into the Mg lattice allows the uniform hydrogen distribution in both the fcc and bcc Mg lattice at a low hydrogen concentration (H:Mg < 0.875) to be more energetically favorable. In addition, this leads to bcc Mg lattice formation with a uniform hydrogen distribution, which is more energetically favorable than the fcc Mg lattice when the atomic ratio H:Mg is near 0.875. In addition, compared with the pure Mg, in the Al-doped Mg, the phase transition from the hcp to the fcc structure with a uniform distribution of H atoms induces less elastic strain. Thus, the uniform hydrogen distribution is more favorable, leading to faster hydrogen absorption. Pure magnesium is characterized by cluster-like hydrogen distribution, which decreases the hydrogen diffusion rate. This leads to the accumulation of a higher hydrogen concentration in magnesium with aluminum compared with pure magnesium under the same hydrogenation regimes, which is confirmed experimentally.
RESUMEN
The study of hydrogen storage properties of Mg-based thin films is of interest due to their unique composition, interface, crystallinity, and high potential for use in hydrogen-storage systems. Alloying Mg with Al leads to the destabilization of the magnesium hydride reducing the heat of reaction, increases the nucleation rate, and decreases the dehydriding temperature. The purpose of our study is to reveal the role of the aluminum atom addition in hydrogen adsorption and accumulation in the Mg-H solid solution. Ab initio calculations of aluminum and hydrogen binding energies in magnesium were carried out in the framework of density functional theory. Hydrogen distribution and accumulation in Mg and Mg-10%Al thin films were experimentally studied by the method of glow-discharge optical emission spectroscopy and using a hydrogen analyzer, respectively. It was found that a hydrogen distribution gradient is observed in the Mg-10%Al coating, with more hydrogen on the surface and less in the bulk. Moreover, the hydrogen concentration in the Mg-10%Al is lower compared to Mg. This can be explained by the lower hydrogen binding energy in the magnesium-aluminum system compared with pure magnesium.
RESUMEN
The current work is devoted to developing a system for the complex research of metal-hydrogen systems, including in an in situ mode. The system consists of a controlled gas reactor with a unique reaction chamber, a radioisotope positron source, and a positron annihilation spectroscopy complex. The use of the system enables in situ investigation of the defect structure of solids in hydrogen sorption-desorption processes at temperatures up to 900 °C and pressures up to 50 bar. Experimental investigations of magnesium and magnesium hydride during thermal annealing were carried out to approve the possibilities of the developed complex. It was shown that one cycle of magnesium hydrogenation-dehydrogenation resulted in the accumulation of irreversible hydrogen-induced defects. The defect structure investigation of the magnesium-hydrogen system by positron annihilation techniques was supplemented with a comprehensive study by scanning electron microscopy, X-ray diffraction analysis, and hydrogen sorption-desorption studies.