Multi-Principal Element Alloys for Solid-State Hydrogen Buffering: A Comprehensive Meta-Analysis of CALPHAD Modeling, Thermodynamic Parameters, and Kinetic Reversibility

The transition toward a zero-emission energy infrastructure depends heavily on the creation of reliable, high-capacity hydrogen storage frameworks. Traditional binary hydrides are often limited by irreversible structural degradation and inflexible thermodynamic limits. In contrast, multi-principal element alloys, frequently referred to as high-entropy alloys (HEAs), offer a groundbreaking pathway for solid-state hydrogen containment. By exploiting maximized configurational entropy, these advanced materials form stable solid-solution phases that demonstrate exceptional durability against cyclic fatigue and phase segregation. This manuscript provides a rigorous meta-analysis of the thermodynamic mechanisms governing HEA hydrides. We critically evaluate the empirical design constraints—specifically Valence Electron Concentration (VEC), atomic size disparity (δ), the Omega parameter (Ω), and mixing enthalpy (ΔHmix )—and investigate the role of CALPHAD modeling with sublattice configurations in accelerating alloy discovery. Furthermore, we dissect the unique graphical signatures of HEA pressure-composition-temperature (PCT) profiles. By synthesizing the most advanced alloy formulations and highlighting current technological bottlenecks, this review outlines a strategic blueprint for achieving commercially viable, room-temperature reversible hydrogen storage systems