In situ hydrogenolysis-engineered Ti_xC MXenes synergistically enhance hydrogen storage in magnesium

Two-dimensional (2D) transition metal carbides (a MXene material) have garnered significant attention owing to their exceptional catalytic performance in magnesium-based hydrogen storage systems. However, existing studies on metal-based MXene catalysts have predominantly focused on elucidating how multivalent metal species facilitate hydrogen transport pathways, while largely neglecting the structural configuration, spatial distribution, and mechanistic roles of carbon components within these materials. Herein, we first study the intrinsic mechanism of in situ hydrogenolysis-engineering of representative Ti-based MXene (Ti_xC) systems based on density functional theory (DFT) calculations. Subsequently, these theoretical results are experimentally validated through comprehensive characterization and hydrogen storage performance evaluations for Ti_xC-doped MgH₂ composites that were synthesized via mechanical ball milling under a 40 bar H₂ atmosphere. Key findings reveal that the hydrogen-driven structural reorganization of Ti_xC spontaneously generates graphene-like carbon layers and Ti active species during ball milling. These carbon encapsulations of MgH₂ with doped Ti-containing catalytic species not only effectively inhibit grain agglomeration but also synergistically enhance hydrogen diffusion kinetics. Hence, the dehydrogenation temperature of MgH₂@Ti₂C decreased from 360 °C to 290 °C compared with pure MgH₂, while the capacity retention rate increased from 62 % to 97 %. This work addresses the dual roles of MXene for enhancing Mg-based hydrogen storage systems, providing critical insights into the design of efficient catalytical material.