Effect of TiO2 nanoparticles on the hydrogen sorption characteristics of magnesium hydride

Effect of LaCoO3 Synthesized via Solid-State Method on the Hydrogen Storage Properties of MgH2

One of the ideal energy carriers for the future is hydrogen. It has a high energy density and is a source of clean energy. A crucial step in the development of the hydrogen economy is the safety and affordable storage of a large amount of hydrogen. Thus, owing to its large storage capacity, good reversibility, and low cost, Magnesium hydride (MgH₂) was taken into consideration. Unfortunately, MgH₂ has a high desorption temperature and slow ab/desorption kinetics. Using the ball milling technique, adding cobalt lanthanum oxide (LaCoO₃) to MgH₂ improves its hydrogen storage performance. The results show that adding 10 wt.% LaCoO₃ relatively lowers the starting hydrogen release, compared with pure MgH₂ and milled MgH₂. On the other hand, faster ab/desorption after the introduction of 10 wt.% LaCoO₃ could be observed when compared with milled MgH₂ under the same circumstances. Besides this, the apparent activation energy for MgH₂-10 wt.% LaCoO₃ was greatly reduced when compared with that of milled MgH₂. From the X-ray diffraction analysis, it could be shown that in-situ forms of MgO, CoO, and La₂O_3, produced from the reactions between MgH₂ and LaCoO₃, play a vital role in enhancing the properties of hydrogen storage of MgH₂.

Influence of Defects on the Stability and Hydrogen-Sorption Behavior of Mg-Based Hydrides

This review deals with the destabilization methods for improvement of storage properties of metal hydrides. Both theoretical and experimental approaches were used to point out the influence of various types of defects on structure and stability of hydrides. As a case study, Mg, and Ni based hydrides has been investigated. Theoretical studies, mainly carried out within various implementations of DFT, are a powerful tool to study mostly MgH₂ based materials. By providing an insight on metal-hydrogen bonding that governs both thermodynamics and hydrogen kinetics, they allow us to describe phenomena to which experimental methods have a limited access or do not have it at all: to follow the hydrogen sorption reaction on a specific metal surface and hydrogen induced phase transformations, to describe structure of phase boundaries or to explain the impact of defects or various additives on MgH₂ stability and hydrogen sorption kinetics. In several cases theoretical calculations reveal themselves as being able to predict new properties of materials, including the ways to modify Mg or MgH₂ that would lead to better characteristics in terms of hydrogen storage. The influence of ion irradiation and mechanical milling with and without additives has been discussed. Ion irradiation is the way to introduce a well-defined concentration of defects (Frankel pairs) at the surface and sub-surface layers of a material. Defects at the surface play the main role in sorption reaction since they enhance the dissociation of hydrogen. On the other hand, ball-milling introduce defects through the entire sample volume, refine the structure and thus decrease the path for hydrogen diffusion. Two Severe Plastic Deformation techniques were used to better understand the hydrogenation/dehydrogenation kinetics of Mg- and Mg₂ Ni-based alloys: Equal-Angular-Channel-Pressing and Fast-Forging. Successive ECAP passes leads to refinement of the microstructure of AZ31 ingots and to instalment therein of high densities of defects. Depending on mode, number and temperature of ECAP passes, the H-sorption kinetics have been improved satisfactorily without any additive for mass H-storage applications considering the relative speed of the shaping procedure. A qualitative understanding of the kinetic advanced principles has been built. Fast-Forging was used for a "quasi-instantaneous" synthesis of Mg/Mg₂ Ni-based composites. Hydrogenation of the as-received almost bi-phased materials remains rather slow as generally observed elsewhere, whatever are multiple and different techniques used to deliver the composite alloys. However, our preliminary results suggest that a synergic hydrogenation / dehydrogenation process should assist hydrogen transfers from Mg/Mg₂ Ni on one side to MgH₂ /Mg₂ NiH₄ on the other side via the rather stable a-Mg₂ NiH_0.3 , acting as in-situ catalyser.

Graphene decorated with Fe nanoclusters for improving the hydrogen sorption kinetics of MgH2 – experimental and theoretical evidence

Graphene decorated with Fe clusters is proposed to be a possible alternative catalyst for the hydrogenation and dehydrogenation reactions of MgH₂.

A co-precipitated Mg–Ti nano-composite with high capacity and rapid hydrogen absorption kinetics at room temperature

A Mg–Ti nano-composite was co-precipitated through an adapted Rieke method, which exhibits high capacity and superior absorption kinetics at room temperature (∼6.2 wt% within 2 h).