The role of catalysts in enhancing the hydrogen storage kinetics of the Mg/MgH₂ system is pivotal. However, the exploration of efficient catalysts and the underlying principles of their design remain both a prominent focus and a significant challenge in current research. In this study, we present a bimetallic oxide of Bi₂Ti₂O₇ hollow sphere as a highly effective catalyst for MgH₂. As a result, the Bi₂Ti₂O₇-catalyzed Mg/MgH₂ system lowers the hydrogen desorption initiation temperature to 194.3 °C, reduces the peak desorption temperature to 245.6 °C, decreases the dehydrogenation activation energy to 82.14 kJ·mol⁻¹, and can absorb 5.4 wt.% of hydrogen within 60 s at 200 °C,demonstrating outstanding hydrogen ab/desorption kinetics, compared to pure MgH₂. Additionally, it can maintain a high hydrogen capacity of 5.2 wt.%, even after 50 dehydrogenation cycles, showing good cycle stability. The characterization results show that the high-valent Bi and Ti in Bi₂Ti₂O₇ are reduced to their low-valent or even zero-valent metallic states during the dehydrogenation and hydrogenation process, thus establishing an in-situ multivalent and multi-element catalytic environment. Density functional theory calculations further reveal that the synergistic effects between Bi and Ti in the Bi-Ti mixed oxide facilitate the cleavage of Mg-H bonds and lower the kinetic barrier for the dissociation of hydrogen molecules, thereby substantially enhancing the kinetics of the Mg/MgH₂ system. This study presents a strategic method for developing efficient catalysts for hydrogen storage materials by harnessing the synergistic effects of metal elements.

The mechanism governing the pseudocapacitive lithium storage behavior is one of the most critical unsolved issues in conversion-type anodes for lithium-ion batteries. In this work, we, for the first time, demonstrate that the pseudocapacitive capability of iron oxide-based anodes is closely associated with the electronic structures of iron ions. As proof of concept, the introduction of amorphization, nitrogen doping, and oxygen vacancies reduces the coordination of iron ions and contributes significantly to the pseudocapacitive lithium storage capability of iron oxide, reaching up to 96% of the specific capacity at 1 mV·s⁻¹. Due to the significantly modulated coordination environment, the 3d electrons of Fe(II) are delocalized with increased spin state and the energy band gap is narrowed, accompanied by an upshift of Fermi energy. The redox activity and carrier mobility of iron oxides are substantially increased, which substantially enhance the exchange current density and thereby improve the pseudocapacitive capability of iron oxide.