Volume 20, Issue 10 p. 1340-1347
Article

Morphology-Dependent Stability of Complex Metal Hydrides and Their Intermediates Using First-Principles Calculations

Dr. ShinYoung Kang

Corresponding Author

Dr. ShinYoung Kang

Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550 USA

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Dr. Tae Wook Heo

Dr. Tae Wook Heo

Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550 USA

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Dr. Mark D. Allendorf

Dr. Mark D. Allendorf

Sandia National Laboratories, 7011 East Ave, Livermore, CA 94550 USA

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Dr. Brandon C. Wood

Corresponding Author

Dr. Brandon C. Wood

Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550 USA

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First published: 18 March 2019
Citations: 12

Graphical Abstract

Hydrogen storage: In complex metal hydrides, morphology is shown to significantly affect the energy landscape, providing key insights into the expression of reaction intermediates.

Abstract

Complex light metal hydrides are promising candidates for efficient, compact solid-state hydrogen storage. (De)hydrogenation of these materials often proceeds via multiple reaction intermediates, the energetics of which determine reversibility and kinetics. At the solid-state reaction front, molecular-level chemistry eventually drives the formation of bulk product phases. Therefore, a better understanding of realistic (de)hydrogenation behavior requires considering possible reaction products along all stages of morphological evolution, from molecular to bulk crystalline. Here, we use first-principles calculations to explore the interplay between intermediate morphology and reaction pathways. Employing representative complex metal hydride systems, we investigate the relative energetics of three distinct morphological stages that can be expressed by intermediates during solid-state reactions: i) dispersed molecules; ii) clustered molecular chains; and iii) condensed-phase crystals. Our results verify that the effective reaction energy landscape strongly depends on the morphological features and associated chemical environment, offering a possible explanation for observed discrepancies between X-ray diffraction and nuclear magnetic resonance measurements. Our theoretical understanding also provides physical and chemical insight into phase nucleation kinetics upon (de)hydrogenation of complex metal hydrides.

Conflict of interest

The authors declare no conflict of interest.