Abstract
Mg−Li alloy possesses a high hydrogen capacity. However, the hydrogenation and dehydrogenation performances are still far from practical application. In this work, Mg2Si (MS) and graphene (G) were employed together to synergistically improve the hydrogen storage properties of Mg−Li alloy. The structures of the samples were studied by XRD and SEM methods. The hydrogen storage performances of the samples were studied by nonisothermal and isothermal hydrogenation and dehydrogenation, thermal analysis, respectively. It is shown that the onset dehydrogenation temperature of Mg−Li alloy was synergistically reduced from 360°C to 310°C after co-addition of Mg2Si and graphene. At a constant temperature of 325°C, the Mg−Li−MS−G composite can release 2.7 wt.% of hydrogen within 2 h, while only 0.2 wt.% of hydrogen is released for the undoped Mg−Li alloy. The hydrogenation activation energy of the Mg−Li−MS−G composite was calculated to be 86.5 kJ mol−1. Microstructure and hydrogen storage properties studies show that graphene can act as a grinding aid during the ball milling process, which leads to a smaller particle size for the composites. This work demonstrates that coaddition of Mg2Si and graphene can synergistically improve the hydrogen storage properties of Mg−Si alloy and offers an insight into the role of graphene in the Mg−Li−MS−G composite.
Highlights
Hydrogen storage remains a big challenge for the large-scale application of hydrogen energy
The hydrogenation of the Mg−Li alloy was not affected by the addition of Mg2Si or graphene
The dehydrogenation of the Mg−Li alloy was synergistically improved by co-addition of Mg2Si and graphene
Summary
Hydrogen storage remains a big challenge for the large-scale application of hydrogen energy. Mg−Li alloys were reported to possesses better hydrogen storage performances than metals Mg or Li (Lan et al, 2016; Halim and Ismail, 2017; Wu et al, 2018). Addition of carbon materials had been considered an effective way to improve the hydrogen storage properties of MgH2 or Mg-based hydrogen storage alloys. Inspired by the above-mentioned discussions, we performed a systematic investigation on the effects of Mg2Si and graphene on the hydrogenation and dehydrogenation properties of Mg−Li alloys in this work. The following will show that Mg2Si and graphene have synergetic enhancing effect on the dehydrogenation properties of MgH2. Such fundamental investigation may provide useful guidance for the design and development of high-performance Mg−Li alloys
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