Titanium‒Nickel Dual Active Sites Enabled Reversible Hydrogen Storage of Magnesium at 180 °C with Exceptional Cycle Stability.

Abstract

Enhancing hydrogenation and dehydrogenation (de/hydrogenation) kinetics without compromising cycle stability is a major challenge for Mg-based hydrogen storage materials (Mg/MgH₂). The de/hydrogenation reactions of Mg/MgH₂ are one of the gas-solid reactions involving hydrogen adsorption, dissociation, diffusion, and nucleation, which often results in the catalysts being unable to simultaneously accelerate these distinct kinetic processes. Here, the Mg₂Ni@Ti─MgO catalyst with dual active sites is reported to be designed to address this issue. The stabilization of Ti²⁺ and Ti³⁺ valence states in the MgO lattice simultaneously accelerates hydrogen adsorption and dissociation. Additionally, Mg₂Ni serves as a hydrogen diffusion and nucleation center, synergistically enhancing de/hydrogenation reactions. Consequently, it enables MgH₂ to release 5.28 wt.% H₂ in 2 min at 280 °C, and achieves 1.96 wt.% H₂ of hydrogen release in 60 min at 180 °C. The Mg₂Ni@Ti─MgO catalyst exhibits remarkable chemical stability at the interfacial structure, minimizing structural and chemical degradation impact, and realizing excellent de/hydrogenation performance over 1000 cycles. These results provide a new methodology for optimizing multiple kinetic steps, attaining highly efficient and stable de/hydrogenation reactions.