Ni-Doped Carbon Nanotube-Mg(BH₄)₂ Composites for Hydrogen Storage

Borohydride magnesium is widely studied as a promising hydrogen storage material due to its high gravimetric and volumetric density (14.9 wt % and 112 g/L, respectively). Different types of catalysts play a good catalytic role in enhancing the hydrogen desorption rates in borohydride systems. In the present paper, multiwalled carbon nanotubes supported Ni (Ni/MWCNTs) were synthesized by a chemical reduction method, and the catalyst was introduced into Mg(BH4)2 to enhance the dehydrogenation kinetics. The effect of Ni/MWCNTs on the microstructural evolution and hydrogen storage properties of Mg(BH4)2 is studied. The Mg(BH4)2-5wt% Ni/MWCNTs (95M@5NiMWCNTs) sample exhibits the best hydrogen storage performance; it starts to release hydrogen at 93 °C, which is 113 °C lower than that of the primary Mg(BH4)2 sample. Moreover, it takes only 3600 s to desorb hydrogen completely at 300 °C, showing a significant improvement on hydrogen desorption kinetics. In comparison with the primary Mg(BH4)2 sample, the dehydriding apparent activation energy of the 95M@5Ni3MWCNTs2 sample is significantly lowered to 119.5 kJ mol–1. Transmission electron microscopy analysis exhibits that the striking improvement of dehydriding properties of Mg(BH4)2 is mainly due to the synergistic catalysis of Ni and MWCNTs. This work provides a new method for designing and synthesizing high-performance catalysts in borohydride hydrogen storage materials, which is potentially utilized as a hydrogen supplier for hydrogen fuel cells.