Regulation of the integrated hydrogen storage properties of magnesium hydride using 3D self-assembled amorphous carbon-embedded porous niobium pentoxide

Abstract

Three different types of porous niobium pentoxide, namely, porous niobium pentoxide (p-Nb₂O₅), carbon-embedded porous niobium pentoxide (C-p-Nb₂O₅), and non-porous niobium pentoxide (np-Nb₂O₅), were prepared by the wet chemical method and employed to improve the hydrogen storage properties of magnesium hydride (MgH₂). It was found that C-p-Nb₂O₅ played an important role in improving the hydrogen storage performance of MgH₂. The C-p-Nb₂O₅-doped and p-Nb₂O₅-doped MgH₂ samples had the same dehydrogenation temperature of 181 °C, which was lower than those of the np-Nb₂O₅-doped (200 °C) and undoped MgH₂ (300 °C) samples. The catalytic effect of C-p-Nb₂O₅ on the hydrogen storage performance of MgH₂ was better than those of p-Nb₂O₅ and np-Nb₂O₅. The dehydrogenation apparent activation energy of C-p-Nb₂O₅-doped MgH₂ (69.3 kJ mol⁻¹) was 7.4 kJ mol⁻¹, 12.8 kJ mol⁻¹, and 72.2 kJ mol⁻¹ lower than those of p-Nb₂O₅-doped MgH₂, np-Nb₂O₅-doped MgH₂, and undoped MgH₂, respectively, and their catalytic effect on the hydrogen storage performance of MgH₂ was in the order of C-p-Nb₂O₅ > p-Nb₂O₅ > np-Nb₂O₅. The mechanism analysis indicated that partial Nb₂O₅ reacted with MgH₂ to form NbO and MgO during the milling process. Under the combined effect of C, Nb₂O₅, and in situ formed NbO, the C-p-Nb₂O₅-doped MgH₂ sample manifested an excellent comprehensive hydrogen storage performance.