• NiS2–MXene hybrid composite synthesized via one-step hydrothermal method reduces MgH2 dehydrogenation temperature by 118°C (from 310°C to 192°C).
• The composite releases 5.87 wt% H2 within 12 minutes at 300°C and absorbs ~2.96 wt% H2 from room temperature to 50°C, demonstrating excellent kinetics.
• Activation energies for hydrogenation and dehydrogenation are reduced by 33.7 and 40.6 kJ·mol−1, respectively, compared to pure MgH2.
• Synergistic mechanisms include multivalent Ti in MXene for electron transport, in situ formed Mg2Ni/Mg2NiH4 and MgS phase interfaces providing active sites, and MXene's high surface area preventing catalyst agglomeration.