In situ diffraction studies of phase-structural transformations in hydrogen and energy storage materials: An overview

The paper presents an overview of advanced in situ diffraction studies as a highly valuable tool to probe the structure and reacting mechanisms of hydrogen and energy storage materials. These studies offer benefits from the use of a high flux diffraction beam in combination with high resolution measurements, and allow, even when using very small samples, establishing the mechanism of the phase-structural transformations and their kinetics based on a rapid data collection for the various charge-discharge states at variable test conditions. The applied conditions include a broad range of hydrogen/deuterium pressures, from vacuum to high pressures reaching 1000 bar H2/D2, and temperatures, from cryocooling (2 K) to as high as 1273 K (1000 degrees C). Simultaneously, various state-of-charge and discharge are probed when studying metal-H/D systems for hydrogen/deuterium gas storage and as anode electrodes of metal hydride batteries. The range of the studied systems includes but is not limited to the AB5, AB2 Laves type, AB, equiatomic ternary ABC intermetallics and Mg-containing layered AB3 structures and composites. Prospects on Li-ion full cells are considered as well. Interrelations between the structure and hydrogen storage performance, including maximum and reversible H storage capacity, hysteresis of hydrogen absorption and desorption, H2 absorption and desorption in dynamic equilibrium conditions, are considered and related to the ultimate goal of optimisation of the H storage behaviours of the advanced H storage materials. Numerous contributions of Dr. Michel Latroche to the field are highlighted, particularly in in situ studies during electrochemical transformations. The paper summarises a long-standing collaboration of the co-authors in the field, which also included 29 joint topical publications with Dr. Michel Latroche, and references 163 original publications. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).