Cation-induced topical disordered niobium nickel oxide for robust hydrogen storage in magnesium hydride

Abstract

Catalytic doping is one of the economic and efficient strategies to optimize the operating temperature and kinetic behavior of magnesium hydride (MgH₂). Herein, efficient regulation of electronic and structural rearrangements in niobium-rich nickel oxides was achieved through precise compositional design and niobium cation functionalized doping, thereby greatly enhancing its intrinsic catalytic activity in hydrogen storage systems. As the niobium concentration increased, the Ni-Nb catalysts transformed into a mixed state of multi-phase nanoparticles (composed of nickel and niobium-rich nickel oxides) with smaller particle size and uniform distribution, thus exposing more nucleation sites and diffusion channels at the MgH₂/Mg interface. In addition, the additional generation of active Ni-Nb-O mixed phase induced numerous highly topical disordered and distorted crystalline, promoting the transfer and reorganization of H atoms. As a result, a stable and continuous multi-phase/component synergistic catalytic microenvironment could be constructed, exerting remarkable enhancement on MgH₂'s hydrogen storage performance. After comparative tests, Ni_0.7Nb_0.3-doped MgH₂ presented the optimal low-temperature kinetics with a dehydrogenation activation energy of 78.8 kJ·mol⁻¹. The onset dehydrogenation temperature of MgH₂+10 wt% Ni_0.7Nb_0.3 was reduced to 198 °C and 6.18 wt% H₂ could be released at 250 °C within 10 min. In addition, the dehydrogenated MgH₂NiNb composites absorbed 4.87 wt% H₂ in 10 min at 125 °C and a capacity retention rate was maintained at 6.18 wt% even after 50 reaction cycles. In a word, our work supplies fresh insights for designing novel defective-state multiphase catalysts for hydrogen storage and other energy related field.