Synthesis of porous Ni@rGO nanocomposite and its synergetic effect on hydrogen sorption properties of MgH2

Abstract

A porous Ni@rGO nanocomposite was successfully prepared by the ethylene glycol method followed by an annealing process. It was shown that fcc Ni nanoparticles anchored on reduced graphene oxide sheets producing a porous structure. It was also found that Ni@rGO nanocomposite had a good catalytic effect on de/hydrogenation of MgH₂. The MgH₂–5 wt% Ni@rGO composite acquired by ball milling exhibited improved faster sorption kinetics and relatively lower sorption temperature than pure MgH₂. The desorption peak temperature shifted from 356 °C for pure milled MgH₂ to 247 °C for MgH₂–5 wt% Ni@rGO. The MgH₂–5 wt% Ni@rGO composite could desorb 6.0 wt% H₂ within 10 min at 300 °C even after nine cycles, in contrast, only 2.7 wt% H₂ was desorbed even after 120 min for undoped MgH₂. In addition, the activation energy (E_a) decreased significantly compared to MgH₂ and the presence of a few layer reduced graphene oxide sheets on the MgH₂ surface prevented the nanograins sintering and agglomeration during cycling, which enhanced the MgH₂ decomposition and cycling stability. It was suggested that the porous Ni@rGO composite had a synergetic effect on the MgH₂ sorption properties.