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Magnesium hydride (MgH2) has become a very promising hydrogen storage material because of its high hydrogen storage capacity, good reversibility and low cost. However, high thermodynamic stability and slow kinetic performance of MgH2 limit its practical application. In the past few decades, many alternative methods have been designed to solve this problem. A large number of studies have demonstrated that the use of metal catalyst doping modification, MgH2 nanocrystallization and other methods can greatly improve the hydrogen absorption and dehydrogenation performance of MgH2. Therefore, this paper reviews and summarizes the modification effect of transition metal catalyst doping on the hydrogen storage performance of MgH2, especially the catalysis on the de/rehydrogenation performance of MgH2. In addition, promoting effects of carbon materials, transition metal alloys and compounds on the hydrogen storage performance of MgH2 were also summarized. Finally, the existing problems and challenges of MgH2 as hydrogen storage materials are discussed, and some possible strategies are proposed. [ABSTRACT FROM AUTHOR]

Due to its high hydrogen storage efficiency and safety, Mg/MgH2 stands out from many solid hydrogen storage materials and is considered as one of the most promising solid hydrogen storage materials. However, thermodynamic/kinetic deficiencies of the performance of Mg/MgH2 limit its practical applications for which a series of improvements have been carried out by scholars. This paper summarizes, analyzes and organizes the current research status of the hydrogen storage performance of Mg/MgH2 and its improvement measures, discusses in detail the hot studies on improving the hydrogen storage performance of Mg/MgH2 (improvement measures, such as alloying treatment, nano-treatment and catalyst doping), and focuses on the discussion and in-depth analysis of the catalytic effects and mechanisms of various metal-based catalysts on the kinetic and cyclic performance of Mg/MgH2. Finally, the challenges and opportunities faced by Mg/MgH2 are discussed, and strategies to improve its hydrogen storage performance are proposed to provide ideas and help for the next research in Mg/MgH2 and the whole field of hydrogen storage. [ABSTRACT FROM AUTHOR]

• Nano NiO/C catalysts were prepared by ultrasonic oscillation and calcination. • Hydrogen could be released at 195 °C and absorbed at 50 °C for the composite. • De/hydrogenation activation energy of the composite were significantly reduced. • The composite material had good cyclic reversibility. • Ab initio calculations showed that NiO and Mg 2 Ni could improve the diffusivity of H atoms. Magnesium based solid hydrogen storage material (MgH 2) has the advantages of good safety and high hydrogen storage capacity in the shipping field. However, the high hydrogen absorption and desorption temperature have not been well solved. Herein, this work proves that it is very effective to improve the hydrogen storage performance of MgH 2 by doping nano NiO/C catalyst. Specifically, experimental results showed that MgH 2 + 9 wt% NiO/C composite could dehydrogenate at 195 °C, which was 155 °C lower than pure MgH 2. In addition, 6.21 wt% H 2 could be released rapidly at 300 °C for 10 min. After complete dehydrogenation, the absorption rate of hydrogen is 50 °C, which is 80 °C lower than that of pure MgH 2. Moreover, 5.13 wt% H 2 could be absorbed within 1 h at 125 °C and 3 MPa hydrogen pressure. In addition, dehydrogenation and hydrogen absorption apparent activation energies of MgH 2 + 9 wt% NiO/C composite are 70.26 kJ/mol and 25.55 kJ/mol lower than those of pure MgH 2 , respectively. The cycle experiment showed that MgH 2 + 9 wt% NiO/C had excellent cycle stability and could maintain 98.8% hydrogen storage capacity after 20 cycles. Furthermore, the study of the catalytic mechanism indicated that NiO/C catalyst is evenly distributed on the surface of MgH 2. More importantly, Mg 2 Ni/Mg 2 NiH 4 is generated in situ, which acts as a "hydrogen pump" and speeds up hydrogen diffusion during the hydrogen absorption and desorption cycle. [ABSTRACT FROM AUTHOR]