Effect of MOF-derived carbon–nitrogen nanosheets co-doped with nickel and titanium dioxide nanoparticles on hydrogen storage performance of MgH2

Abstract

Magnesium hydride (MgH2) is considered one of the most ideal materials for hydrogen storage. However, the practical applications of MgH2 are greatly hindered by its high operating temperature and poor hydrogen storage kinetics. In the present work, carbon–nitrogen nanosheets co-doped with disk-like nickel and titanium dioxide nanoparticles ((Ni, TiO2)CN) were prepared using metal–organic frameworks (MOFs) as precursors to improve the hydrogen storage performance of MgH2. The as-synthesized ((Ni, TiO2)CN)-doped MgH2 system manifested excellent hydrogen storage properties at low temperatures and could absorb 5.08 wt% of hydrogen in 100 min at 40 °C and 6.17 wt% of hydrogen in 10 min at 125 °C. The dehydrogenation activation energy of the ((Ni, TiO2)CN)-doped MgH2 system was obtained as 83.1 kJ∙mol−1, which was considerably lower than that of pure MgH2. The mechanism analysis revealed that Ni reacted with Mg to form Mg2Ni coating around Mg, the in situ Mg2Ni and its hydride (Mg2NiH4) acted as a “hydrogen pump” to drive hydrogen diffusion and dissociation. And the mutual reversible change in polyvalent Ti ions could promote the transfer of charge, which was conducive to accelerating the formation of Mg/MgH2. Additionally, stable CN layers not only could inhibit the fragmentation and agglomeration of MgH2 particles, but also could make the active substance dispersed more evenly; thus, the cycle stability and hydrogen absorption and desorption kinetics of MgH2 was greatly enhanced under the synergistic catalysis of in situ formed Mg2Ni/Mg2NiH4, polyvalent titanium, and N-C nanosheets. The findings of this work could provide a new strategy to improve the properties of Mg-based hydrogen storage materials.