DFT analysis of physical properties and solid-state hydrogen storage potential of Sodium-Based Double Perovskites Na 2 XH 6 (X = V, Cr and Co)

Abstract

This study investigates novel hydrogen storage materials Na 2 XH 6 (X = V, Cr and Co) using first-principles density functional theory (DFT) within the GGA-PBE approximation, as implemented in the CASTEP code. The structural, electronic, mechanical, optical and thermal properties are systematically analyzed. Gravimetric capacities (Cwt.%) are 5.88%, 5.81% and 5.45% for Na 2 VH 6 , Na 2 CrH 6 and Na 2 CoH 6 , respectively. Geometry optimization yields stable structures with lattice constants of 7.65Å, 7.50 Å and 7.24Å. Negative formation enthalpies confirm thermodynamic stability, while band structure analysis reveals metallic character. Mechanical stability is verified by calculated elastic constants (C 11 , C 12 and C 44 ) satisfying the Born-Huang criteria.