Studies On Properties And Reaction Mechanisms Of MgH₂ Based Hydrogen Storage Composites Materials

Among those emerged solid hydrogen storage materials,MgH₂ hydrogen storage materials are very potential candidates for application due to its high hydrogen storage capacity,high hydrogen release purity,simple reaction steps and abundant earth reserves.Targeting to poor kinetic performance of reversible dehydrogenation and high thermal stability,the modification on MgH₂-based hydrogen storage materials was carried out as the following aspects in this paper:?1?A kind of additive,nano-nickel particles over porous carbon materials was prepared and combined with MgH₂ by ball milling.The initial dehydrogenation temperature of MgH₂-Ni/CMK-3 decreases to 433 K,and the dehydrogenation capacity attains 6.5 wt.%H₂.The kinetic performance of MgH₂-Ni/CMK-3 is obviously improved.Around 3.9 wt.%H₂ can be absorbed even at near room temperature of 328 K.Cyclic hydrogen absorption and desorption tests show that the capacity can be maintained at 90%after 10 cycles.Nickel nanoparticles actively participated in the dehydrogenation reaction of MgH₂ to form Mg₂Ni and Mg₆Ni phases.The dehydrogenation enthalpy of the system is reduced by 1.5 kJ mol^-1 H₂^-1.It demonstrated that Ni/CMK-3 additive not only plays a role of catalyst,but also reduces the thermal stability of the system.?2?A bimetallic nano-additive was designed to investigate the effects of composition on the hydrogen storage prperties of MgH₂.And the reaction mechanism was explored.The initial dehydrogenation temperature of MgH₂-Pd₃₀Ni₇₀/CMK-3 was at around 431 K,and the cut-off dehydrogenation temperature was as low as 561 K.The Pd particles reacted with MgH₂ to form Mg₆Pd in the dehydrogenation process,and the phase was reversible.The binding energies of Pd in dehydrogenation products were changed,demonstrating that Pd was involved in dehydrogenation/hydrogen absorption reaction.The enthalpy of dehydrogenation was decreased by 4.9 kJ mol^-1 H₂^-1,indicating that the additive remarkably destabilizes the system.?3?The ternary reaction system of two-dimensional MXene phase Ti₃C₂ doped MgH₂-LiAlH₄ was synthesized.It was found that the dehydrogenation activation energy was decreased to 128 kJ mol^-1,and the hydrogen absorption activation energy was decreased to 65.7 kJ mol^-1.The initial dehydrogenation temperature of 4MgH₂-LiAlH₄-Ti₃C₂ is around 338 K,and the saturated dehydrogenation capacity reaches 6.5 wt.%H₂ at 573 K.There are many dehydrogenation processes in the system,Al and LiH yielded from LiAlH₄ are involved in the dehydrogenation of MgH₂ to produce Al₁₂Mg₁₇ and Li₃Mg₇.Ti formed from the decomposition of Ti₃C₂ participates in the dehydrogenation process.The reaction enthalpies of the system are decreased,indicating that the thermal stability of the system was remarkably reduced.