In-Situ Formed Ni3znc0.7/Carbon Nanotubes Loading on Melamine Sponge-Derived Carbon as Catalyst for Improving Hydrogen Storage Performance of Mgh2

The high operating temperatures and slow kinetics limit the application of MgH2 based hydrogen storage materials. The Ni3ZnC0.7/carbon nanotubes loaded onto melamine sponge-derived carbon (MS) skeleton composites is produced by vacuum filtration followed by calcination method. The Ni3ZnC0.7 nanoparticles of about 5-30nm remain stable during the ball milling process and can not react with MgH2. After dehydrogenation, the Ni3ZnC0.7 reacts with MgH2 and in-situ changes to Mg2Ni/Zn. The MgH2-2.5wt%MS@Ni3ZnC0.7 can absorb 5.18wt% H2 with 200s at 423K and the initial hydrogen release temperature is reduced to 585K. After 20 hydrogen uptake/release cycles, the capacity retention rates are determined to be 88.4% and 94.6% for hydrogenation and dehydrogenation. The transformation of Mg2Ni/Mg2NiH4 provides additional diffusion channels for hydrogen atoms or molecules and can serve as “hydrogen pump” for promoting the de/hydrogenation. Moreover, Zn/MgZn2 provides the active sites for the nucleation of Mg/MgH2. The theoretical calculated MgH2 dissociation energy barrier on the Ni3ZnC0.7 surface is 0.49eV and the Mg-H bond is 1.995Å, much lower than that of MgH2 surface of 1.55eV and higher for Mg-H bond of 1.72Å. This study offers guidance for the design of porous carbon loaded non-stoichiometric metal carbides catalysts to enhance the hydrogen storage properties of MgH2.