Xu Nuo,Yuan Zirui,Ma Zhihong,Guo Xinli,Zhu Yunfeng,Zou Yongjin,Zhang Yao
MgH 2 with a large hydrogen capacity is regarded as a promising hydrogen storage material. However, it still suffers from high thermal stability and sluggish kinetics. In this paper, highly dispersed nano-Ni has been successfully prepared by using the polyol reduction method with an average size of 2.14 nm, which significantly improves the de/rehydrogenation properties of MgH 2 . The MgH 2 —10wt% nano-Ni sample starts releasing H 2 at 497 K, and roughly 6.2wt% H 2 has been liberated at 583 K. The rehydrogenation kinetics of the sample are also greatly improved, and the adsorption capacity reaches 5.3wt% H 2 in 1000 s at 482 K and under 3 MPa hydrogen pressure. Moreover, the activation energies of de/rehydrogenation of the MgH 2 —10wt% nano-Ni sample are reduced to (88 ± 2) and (87 ± 1) kJ·mol −1 , respectively. In addition, the thermal stability of the MgH 2 —10wt% nano-Ni system is reduced by 5.5 kJ per mol H 2 from that of pristine MgH 2 . This finding indicates that nano-Ni significantly improves both the thermodynamic and kinetic performances of the de/rehydrogenation of MgH 2 , serving as a bi-functional additive of both reagent and catalyst.
Lithium hydride (LiH), a saline hydride with a hydrogen density of 12.6 wt %, is highly thermostable, which hinders its extensive application in hydrogen storage. In this study, we demonstrate a distinct photodecomposition of LiH under ambient conditions. Ultraviolet–visible (UV–vis) illumination induces hydrogen release and creates surface hydrogen vacancies on LiH. The subsequent H– migration enables hydrogen desorption and the accumulation of vacancies at the subsurface, resulting in the generation of metallic Li clusters. Rehydrogenation, on the contrary, can be charged under UV–vis illumination in 1 bar H2. Such phenomena show that the thermodynamic and kinetic limits in the re/dehydrogenation of LiH can be broken under illumination, which allows hydrogen storage over the LiH surface at temperatures ∼600 K lower than those of the corresponding thermal process. This work provides new insights into the interaction of semiconducting hydrides and photons and opens an avenue for the development and optimization of materials for hydrogen storage and related photodriven reactions.
Photon-driven chemical processes are usually mediated by oxides, nitrides and sulfides whose photo-conversion efficiency is limited by charge carrier recombination. Here we show that lithium hydride undergoes photolysis upon ultraviolet illumination to yield long-lived photon-generated electrons residing in hydrogen vacancies, known as F centres. We demonstrate that photon-driven dehydrogenation and dark rehydrogenation over lithium hydride can be fulfilled reversibly at room temperature, which is about 600 K lower than the corresponding thermal process. As light-driven F centre generation could provide an alternative approach to charge carrier separation to favour chemical transformations that are kinetically or thermodynamically challenging, we show that light-activated lithium hydride cleaves the N≡N triple bond to form a N–H bond under mild conditions. Co-feeding a N 2 /H 2 mixture with low H 2 partial pressure leads to photocatalytic ammonia formation at near ambient conditions. This work provides insights into the development of advanced materials and processes for light harvesting and conversion.
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