Tuning the reaction mechanism and hydrogenation/dehydrogenation properties of 6Mg(NH₂)₂—9LiH system by adding LiBH₄

‘‘RevHy’’ – ‘‘Study on the synthesis, structures and performances of complex hydrides systems for Reversible high capacity Hydrogen storage at low temperatures’’

Publisher

Elsevier

Series or journal

International Journal of Hydrogen Energy

ISSN

0360-3199

Periodical volume

44

Periodical issue

23

First page

11920

Last page

11929

Part of the university bibliography

✅

Language

English

Keyword

Solid-state hydrogen storage

Amide-hydrides

Li–Mg–N–H system

Abstract

The hydrogen storage properties of 6Mg(NH₂)₂—9LiH-x(LiBH₄) (x =0, 0.5, 1, 2) system and the role of LiBH₄ on the kinetic behaviour and the dehydrogenation/hydrogenation reaction mechanism were herein systematically investigated. Among the studied compositions, 6Mg(NH₂)₂—9LiH—2LiBH₄ showed the best hydrogen storage properties. The presence of 2 mol of LiBH₄ improved the thermal behaviour of the 6Mg(NH₂)₂—9LiH by lowering the dehydrogenation peak temperature nearly 25°C and by reducing the apparent dehydrogenation activation energy of about 40 kJ/mol. Furthermore, this material exhibited fast dehydrogenation (10 min) and hydrogenation kinetics (3 min) and excellent cycling stability with a reversible hydrogen capacity of 3.5 wt % at isothermal 180°C. Investigations on the reaction pathway indicated that the observed superior kinetic behaviour likely related to the formation of Li₄(BH₄)(NH₂)₃. Studies on the rate-limiting steps hinted that the sluggish kinetic behaviour of the 6Mg(NH₂)₂–9LiH pristine material are attributed to an interface-controlled mechanism. On the contrary, LiBH₄-containing samples show a diffusion-controlled mechanism. During the first dehydrogenation reaction, the possible formation of Li₄(BH₄)(NH₂)₃ accelerates the reaction rates at the interface. Upon hydrogenation, this ‘liquid like’ of Li₄(BH₄)(NH₂)₃ phase assists the diffusion of small ions into the interfaces of the amide-hydride matrix.

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