Strain engineering for optimized hydrogen storage: Enhancing ionic conductivity and achieving near-room-temperature desorption in Mg₂NiH₄

Abstract

This study investigates strain engineering to optimize hydrogen storage in Mg₂NiH₄, with a focus on enhancing ionic conductivity and approaching room-temperature desorption. Using density functional theory (DFT), we analysed the effects of uniaxial and biaxial tensile and compressive strains on the structural, mechanical, diffusion kinetics, and electronic properties of Mg₂NiH₄. The activation energy for hydrogen diffusion was found to range from 0.38 to 0.45 eV under different strain conditions. The application of strain significantly influences ionic conductivity, with uniaxial strain resulting in values between 1.18 and 25.5 S/m, and biaxial strain yielding values from 12.3 to 18.3 S/m. Mechanical analysis shows that Mg₂NiH₄ exhibits brittle behaviour across all strain conditions. Additionally, electronic structure analysis indicates that the material maintains its metallic properties under both uniaxial and biaxial strain. Although the study did not achieve room-temperature desorption, it demonstrated significant progress, with desorption occurring at approximately 500 K. These results demonstrate that strain engineering can significantly improve ionic conductivity and facilitate hydrogen desorption closer to practical room temperature, providing valuable insights for optimizing Mg₂NiH₄ for practical hydrogen storage applications.