Construction of carbon covered Mg2NiH4 nanocrystalline for hydrogen storage

•Carbon-covered nanocrystalline Mg2Ni was successfully constructed.•The ab/desorption temperature of Mg-based materials was dramatically reduced.•Mg2Ni with carbon-covered structure exhibited stable cycling performance.•Enhanced thermodynamic and kinetic properties of hydrogenated Mg2Ni was realized. Decreasing the desorption temperature and formation enthalpy are two key challenges for the practical application of magnesium-based hydrogen storage materials. In this paper, different Mg2Ni samples were successfully synthesized, and the corresponding hydrogen storage kinetic and thermodynamic behaviors were investigated. The carbon-covered nanocrystalline Mg2Ni started to take up hydrogen at room temperature and released hydrogen at 180 °C. Meanwhile, the hydrogenated sample fully desorbed hydrogen at 250 °C within 10 min, and absorbed 2.1 wt% hydrogen in 1 h at 125 °C. The absorption and desorption activation energy of carbon-covered nanocrystalline Mg2Ni was calculated to be 20.8 ± 1.2 kJ/mol and 34.1 ± 2.4 kJ/mol, which were 74% and 78% lower than that of MgH2, respectively. The dehydrogenation enthalpy of the carbon-covered nanocrystalline Mg2NiH4 sample was also reduced from 89.9 ± 4.0 kJ/mol of MgH2 to 67.0 ± 0.5 kJ/mol. In addition, the cycling kinetics was maintained after ten cycles. Further analysis revealed that the remarkably improved hydrogen storage property of Mg2NiH4 originated from the combining effect of the alloying, carbon covering, and nanocrystalline strategy.