Hydrogen Diffusion on, into and in Magnesium Probed by DFT: A Review

Abstract

Hydrogen is an energy carrier that can be a sustainable solution for alternative energy with zero greenhouse gas emissions. Hydrogen storage is a key point for hydrogen energy. Metals provide an access for safe, controlled and reversible hydrogen storage and release. Magnesium, due to its outstanding hydrogen storage capacity, high natural abundance, low cost and non-toxicity is one of the most attractive materials for hydrogen storage. The economic efficiency of Mg as a hydrogen accumulator is limited by its sluggish hydrogen sorption kinetics and high stability of its hydride MgH2. Many attempts have been made to overcome these shortcomings. On a microscopic level, hydrogen absorption by metal is a complex multistep process that is impossible to survey experimentally. Theoretical studies help to elucidate this process and focus experimental efforts on the design of new effective Mg-based materials for hydrogen storage. This review reports on the results obtained within a density functional theory approach to studying hydrogen interactions with magnesium surfaces, diffusion on Mg surfaces, into and in bulk Mg, as well as hydrogen induced phase transformations in MgHx and hydrogen desorption from MgH2 surfaces.

Hydrogen Diffusion in the Lower Mantle Revealed by Machine Learning Potentials

“…In addition, higher water concentration may cause additional hydrogen to occupy interstitial sites, obstructing some diffusion pathways, and decelerating hydrogen diffusion, similar to the saturation effect in metal‐hydrogen systems (e.g., Shelyapina, 2022). With respect to the (Mg + 2H) Si defect, since hydrogen atoms mainly reside in interstitial sites, this can also be a potential factor affecting hydrogen diffusivity.…”

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

“…It can be believed that these transformations on hydrogenation can be affected by both external and internal factors and thereby influence the nucleation and growth of the β-MgH 2 . Unfortunately, experimentally only the initial (α-phase) and final states (β-MgH 2 ) can be caught, making the internal fcc structure of MgHx impossible to survey [42].…”

“…It can be believed that these transformations on hydrogenation can be affected by both external and internal factors and thereby influence the nucleation and growth of the β-MgH2. Unfortunately, experimentally only the initial (α-phase) and final states (β-MgH2) can be caught, making the internal fcc structure of MgHx impossible to survey [42]. Many published articles [44][45][46][47][48][49][50] focused on the introduction of kinetic models used to fit experimental hydrogen absorption and desorption data of Mg rather than the scope of application of kinetic models according to kinetic measurement methods.…”