Preparation Of Modified-Carbon-Sphere And Their Effcets On Hydrogrn Storage Properties Of MgH₂

The Mg-based hydrogen storage materials is considered to be one of the most desirable hydrogen storage materials due to its high weight capacity and low price.However,its relatively high operating temperatures and slow dynamics have always hampered its commercial applications.In this paper,based on the modified carbon-sphere as additives,we prepared Mg-based hydrogen storage materials by hydrogenation combustion and mechanical ball milling.The hydrogen storage performances of composite materials were studied,and the reaction mechanisms were further studied.N-doped carbon spheres?NCS?were synthesized by hydrothermal method,and introduced into Mg to form an Mg H₂–NCS composites by hydriding combustion and subsequent high-energy ball milling.The onset dehydrogenation temperature of composite decreased by 23 K,and hydrogen desorption activation energy decreased by 20.3 kJ/mol.At 473 K and 3 MPa H₂,the composite can absorb 4.2 wt.%H₂ in 3600 s.The analysis showed that carbon has a good dispersion effect on the composite system and improves the hydrogen storage performance of the composite.Nano-nickel particles coated nitrogen-doped carbon spheres?Ni@NCS?were synthesized by chemical reduction method,and then introduced into Mg to form an MgH₂–Ni@NCS composite via a hydriding combustion and subsequent high-energy ball milling process.Results showed that the MgH₂–Ni@NCS composite owned a high hydrogen storage capacity and fast absorbing/desorbing kinetics,desorbing 4.3 wt.%H₂and absorbing 5.7 wt.%H₂ within 8 min at 623 K.Even at relatively low temperature?373K?,MgH₂–Ni@NCS composite still absorbed 4.2 wt.%H₂ within 60 min compared to 0.9wt.%H₂ for the milled MgH₂.The improvement in hydrogen storage properties is ascribed to that an in-situ formed Mg₂NiH₄ induced dehydrogenation of MgH₂,and that the carbon materials effectively prevented the agglomeration of magnesium during the hydriding/dehydriding reaction.FeNi₃ particles supported nitrogen-doped carbon-spheres?FeNi₃@NCS?were synthesized by chemical reduction method.The onset dehydrogenation temperature of composite decreased by 79 K,and activation energy of hydrogen desorption decreased by65.5 kJ/mol.The capacities and rates of de/absorbing hydrogen remained essentially unchanged after 10 cycles.The significant improvements of hydrogen storage performances of MgH₂ are mainly attributed to carbon dispersion,meanwhile in situ generated Mg₂NiH₄ and Fe also play a catalytic effect.