Feeling the strain: Enhancing the thermodynamics characteristics of magnesium nickel hydride Mg2NiH4 for hydrogen storage applications through strain engineering.

This work is based on density functional theory (DFT) and studies the structural, electronic, thermodynamic properties and dehydrogenation kinetics of the hydride Mg 2 NiH 4 under different uniaxial and biaxial strain applied to Mg 2 Ni or Mg 2 NiH 4. structural properties are first studied based on generalized gradient (GGA) and local density (LDA). Thermodynamic and electronic properties and dehydrogenation kinetics are then studied using the GGA method based on the Perdew-Burke-Ernzerhor (PPE) approximation. The results obtained show that uniaxial/biaxial tensile and compressive strains are capable of inducing structural deformation by increasing the value of the strain step on both Mg 2 Ni and Mg 2 NiH 4 , and that these strains applied to Mg 2 NiH 4 are capable of reducing the stability of the system more than strains applied to Mg 2 Ni, due to the contribution of strain energy. More specifically, it lowers the enthalpy of formation to −40 kJ/mol.H 2 under compressive strain ε = −7.5% or biaxial tensile strain ε = +7.8%, which corresponds exactly to the ideal value suggested by the US Department of Energy (DOE) for materials suitable for hydrogen storage. And the decomposition temperature fell within the fuel cell operating range (PEM) of 289–393 K. On the other hand, under uniaxial and biaxial strains, the activation energy of hydrogen atom diffusion in Mg 2 NiH 4 varied between 0.40 eV and 0.22 eV, resulting in a remarkable improvement in dehydrogenation properties. Analysis of the total (TDOS) and partial (PDOS) density curves shows that the Mg 2 NiH 4 system has a metallic characteristic, and that this characteristic is maintained by increasing the strain pitch, with a variation in the energy width of the valence band. [Display omitted] • Improvement in the thermodynamic properties of Mg 2 NiH 4 under strain. • Compressive strain make Mg 2 NiH 4 more competitive for hydrogen storage. • The results meet DOE standards, boosting hydrogen storage potential in Mg 2 NiH 4. • Biaxial tensile strain improves hydrogenation/dehydrogenation kinetics. • Biaxial strain make Mg 2 NiH 4 more suitable for fuel cell (PEM) operation. [ABSTRACT FROM AUTHOR]