Structure-dependent hydrogen sorption and cycling stability of MgH2 enabled by Ti/Ni multiphase catalyst–CNT co-modification

Abstract

MgH₂ is a promising solid-state hydrogen storage material, but its practical application remains limited by sluggish hydrogen sorption kinetics, high thermodynamic stability, and insufficient cycling durability. Herein, a Ti/Ni multiphase catalyst and carbon nanotubes (CNTs) were co-introduced into MgH₂ by ball milling to construct a carbon-coated composite, in which the effects of Ti/Ni ratio and CNT structure on hydrogen-storage behavior were systematically investigated. Among the examined samples, the optimized composite exhibits the best overall performance, with an onset dehydrogenation temperature of 180 °C, rapid hydrogen uptake of 6.0 wt% within 42 s at 200 °C and within 15 s at 275 °C, and hydrogen release of 5.91 wt% within 200 s at 325 °C. The hydrogenation and dehydrogenation activation energy are reduced to 41.59 and 44.98 kJ mol⁻¹, and the hydrogenation/dehydrogenation enthalpy changes are 35.61 and 42.33 kJ mol⁻¹, respectively. In addition, the composite maintains hydrogenation and dehydrogenation capacity retentions of 98.6% and 99.1%, respectively, after 10 cycles. Structural characterization indicates that the improved hydrogen-storage behavior is associated with the formation of TiO₂, NiTi, and Mg₂Ni species together with a carbon coating generated from CNTs. Notably, CNTs with different structural parameters form carbon coatings of different thicknesses after ball milling, which strongly influences hydrogen sorption kinetics and cycling stability. Density functional theory calculations further suggest that Ti/Ni catalyst–CNT co-modification weakens the Mg–H interaction and modifies the electronic structure of MgH₂. This work demonstrates a structure-dependent catalyst–carbon synergistic strategy for improving the hydrogen storage performance of MgH₂.