Mg2NiH4 under stress: Coupling transition metal doping with structural deformation for improved hydrogen storage

We use first-principles DFT to assess transition-metal substitution (Ag, Co, Mn) and uniaxial strain (−3% to +3%) as dual levers to improve Mg 2 NiH 4 for hydrogen storage. Among the dopants, Mn is most effective: the formation enthalpy shifts from −63 to −38 kJ.mol −1 . H 2 under compressive strain, near the DOE target (≈−40 kJ.mol −1 . H 2 ). The corresponding decomposition temperature drops from 502 to 282 K, aligning with the PEMFC operating window (≈289–393 K). Structurally, compressive strain increases the volumetric hydrogen density without compromising reversibility. Kinetically, the H migration barrier decreases from 0.50 to 0.42 eV in the Mn-substituted phase, especially under tensile strain, indicating faster diffusion. These results demonstrate that combining chemical substitution with strain engineering tunes both thermodynamics and kinetics, positioning Mn-doped Mg 2 NiH 4 under ±1% compressive/tensile strain as a practical candidate for low-temperature, fuel-cell-compatible hydrogen storage.