The effects of highly dispersed Ni nano-particles on the hydrogen storage performance of MgH₂

MgH₂ with a large hydrogen capacity has been regarded as a promising hydrogen storage material. However, it still suffers from high thermal stability and sluggish kinetics. In this paper, highly dispersed nano-Ni has been successfully prepared by the polyol reduction method with an average size of 2.14 nm, which significantly improved the de/rehydrogenation properties of MgH₂. The MgH₂-10wt.% nano-Ni sample starts releasing H₂ at 497 K and roughly 6.2wt.% H₂ has been completely liberated at 598 K. The rehydrogenation kinetics of the sample are also greatly improved and the adsorption capacity reaches 5.3wt.% H₂ in 1000 s at 482 K and under 3 MPa hydrogen pressure. Moreover, the activation energies of de/rehydrogenation of the MgH₂-10wt.% nano-Ni sample are reduced to 88 ± 2 kJ mol⁻¹ and 87 ± 1 kJ mol⁻¹, respectively. In addition, the thermal stability of the MgH₂-10wt.% nano-Ni system is reduced by 5.5 kJ (mol H₂)⁻¹ from that of pristine MgH₂. It means that nano-Ni significantly improves both the thermodynamic and kinetic performances of the de/re-hydrogenation of MgH₂, serving as a bi-functional additive of both reagent and catalyst.