Enhanced hydriding–dehydriding performance of a 2LiH–MgB 2 composite by the catalytic effects of Ni–B nanoparticles† Jie Shao, Xuezhang Xiao, Lixin Chen, * Xiulin Fan, Leyuan Han, Shouquan Li, Hongwei Ge and Qidong Wang A system of 2LiH–MgB 2 and its hydrogenated 2LiBH 4 –MgH 2 is an attractive candidate for hydrogen storage. However, its hydriding–dehydriding kinetics have to be further improved for practical application. In the present work, three kinds of Ni–B nanoparticles with different crystalline states and particle sizes were prepared by wet-chemical reduction and mechanochemical methods, and then introduced into a 2LiH–MgB 2 composite for catalytic enhancement. The catalytic roles of Ni–B nanoparticles on the hydriding–dehydriding properties were investigated systematically. The results show that all of the Ni–B nanoparticles can significantly enhance the hydriding–dehydriding kinetics of the 2LiH–MgB 2 composite, resulting in no incubation period for the formation of MgB 2 during dehydrogenation. The more disordered the amorphous structure and the smaller sized the Ni–B particles are, the better the catalytic effect that is obtained. Microstructure analyses clearly reveal the formation of the MgNi 3 B 2 phase in the dehydriding process, which acts as the nucleation agent for MgB 2 formation determined by an edge-to-edge model. Directly doping with Ni–B nanoparticles in the 2LiH–MgB 2 system shows a higher hydrogen desorption capacity of 9.4 wt% and obtains a better catalytic efficiency than doping with NiCl 2 . Introduction The development of safe hydrogen storage technology with a high energy density is a key prerequisite for the widespread usage of hydrogen in mobile applications. 1 Among the current materials for solid-state hydrogen storage application, the LiBH 4 complex has attracted much attention because of its high gravimetric and volumetric hydrogen capacities (18.5 wt% and 121 kg H 2 m 3 ). 2–7 Unfortunately, the use of LiBH 4 as an on- board hydrogen storage material is hampered by unfavorable high thermal stability. 8 Several strategies, like anion substitu- tion 9,10 and nanoconnement 11–13 etc., have been used to modify the hydrogen storage performance of LiBH 4 . Among these methods, incorporating metal hydrides to form reactive hydride composites (RHCs) has been proven to be effective in stabilizing the dehydrogenated state and then lowering the total reaction enthalpy. 14,15 A distinct example of this approach is the 2LiBH 4 – MgH 2 system developed by Vajo et al. 4 This system has a large amount (11.4 wt%) of reversible capacity, as well as a more advantageous dehydrogenation enthalpy (42 kJ per mol H 2 ) due to the formation of MgB 2 in the following reaction: 2LiBH 4 + MgH 2 / 2LiH + MgB 2 + 4H 2 (1) The formation of MgB 2 is considered to be crucial for the reverse reaction 15,16 and a hydrogen back pressure of 3–5 bar should be applied in the reaction chamber during dehydroge- nation to ensure the increased formation of MgB 2 . 17–19 Extensive efforts have been made to further improve the dehydriding–rehydriding kinetics, thermodynamic stability, and cycling performance of the 2LiBH 4 –MgH 2 system for further practical utilization. In particular, it is found that nucleation of MgB 2 from the mixture of Mg and LiBH 4 is quite difficult, which results in a long incubation period between the two dehydrogenation steps and hampers the subsequent dehydriding process. 20 Variation in the addition of suitable additives has a signicant effect on the length of the incubation period, as well as on the reaction kinetics. 21 Recently, many studies have focused on improving the hydrogen storage performance of the 2LiBH 4 –MgH 2 system by milling with transition metal halides or oxides. 22–26 Among them, nickel or nickel compounds are promising dopants to enhance the dehydriding–rehydriding properties of both LiBH 4 27–29 and MgH 2 . 30–32 In our previous work, transition metal chlorides were introduced into the 2LiBH 4 –MgH 2 system and metal borides Key Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, P.R. China. E-mail: lxchen@zju.edu.cn; Fax: +86 571 8795 1152; Tel: +86 571 8795 1152 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ta11600j Cite this: J. Mater. Chem. A, 2013, 1, 10184 Received 22nd April 2013 Accepted 3rd June 2013 DOI: 10.1039/c3ta11600j www.rsc.org/MaterialsA 10184 | J. Mater. Chem. A, 2013, 1, 10184–10192 This journal is ª The Royal Society of Chemistry 2013 Journal of Materials Chemistry A PAPER Published on 03 June 2013. Downloaded by Zhejiang University on 20/08/2013 02:59:32. View Article Online View Journal | View Issue