Density functional theory insights into the structure, electronic and mechanical properties, thermodynamics, and diffusion of high-entropy alloys for hydrogen storage: A review

This review highlights the application of first principles in studying hydrogen interactions within HEAs. It explores key aspects, including electronic, mechanical stability, thermodynamics, and diffusion pathways. Most research uses SQS to simulate chemical disorder, which is paired with GGA-PBE exchange-correlation functionals and PAW pseudopotentials to ensure accurate energetic and structural predictions. Electronically, DFT descriptors such as DOS/PDOS, COHP/ICOHP, bond order, and Mulliken charges have demonstrated that hydrogen stabilization is controlled by localized metal-hydrogen bonding, charge transfer, and element-specific d-1s hybridization, all of which influence interstitial site preference and hydride stability. Mechanically, DFT-derived elastic moduli (B, G, E), Pugh's ratio, and dislocation energy factors show that hydrogen can strengthen or soften HEAs, depending on concentration, phase, and local lattice distortion, influence powder hydride decrepitation and cycle durability. Thermodynamically, hydrogen binding energy emerges as the critical descriptor, requiring an ideal intermediate binding strength for reversible absorption and desorption. DFT exhibits heterogeneous hydrogen transport regulated by competing lattice distortion (trapping) and lattice expansion (enhanced pathways), resulting in diffusion composition and phase dependence. DFT's strengths include unmatched atomistic insight, but it is limited by exchange-correlation approximations, neglect of short-range order, incomplete entropy/zero-point effects, static 0 K models, and high computing cost. Future advancement will be made by combining DFT and machine learning for high-throughput screening in rational HEA design. • Provides the first unified DFT framework for HEA hydrogen-storage mechanisms. • Identifies electronic, thermodynamic, and mechanical descriptors governing H behaviour. • Clarifies hydrogen-induced phase transitions and diffusion in complex HEAs. • Evaluates DFT limitations and required advances for accurate HEA hydride modelling. • Outlines DFT–ML pathways for rational design of high-performance HEA hydrides.