Tuning the reaction mechanism and hydrogenation/dehydrogenation properties of 6Mg(NH2)29LiH system by adding LiBH4

• Published in: International journal of hydrogen energy 2019-05, Vol.44 (23), p.11920-11929
• Main Authors: Gizer, Gökhan, Puszkiel, Julián, Cao, Hujun, Pistidda, Claudio, Le, Thi Thu, Dornheim, Martin, Klassen, Thomas
• Format: Article
• Language: English
• Subjects: Amide-hydrides; Li–Mg–N–H system; Solid-state hydrogen storage
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2019.03.133

The hydrogen storage properties of 6Mg(NH2)29LiH-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)29LiH2LiBH4 showed the best hydrogen storage properties. The presence of 2 mol of LiBH4 improved the thermal behaviour of the 6Mg(NH2)29LiH 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)29LiH 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. •Reaction kinetics of 6Mg(NH2)2-9LiH-x(LiBH4) (x = 0, 0.5, 1, 2) system.•Reduction in the dehydrogenation apparent activation energies.•Excellent cycling properties over 20 cycle.•Rate-limiting processes and the role of Li4(BH4)(NH2)3.