Additively manufactured high-entropy alloys for hydrogen storage: Predictions

This review paper covers an analysis of the empirical calculations, additive manufacturing (AM) and hydrogen storage of refractory high-entropy alloys undertaken to determine the structural compositions, particularly focusing on their applicability in research and experimental settings. The inventors of multi-component high-entropy alloys (HEAs) calculated that trillions of materials could be manufactured from elements in the periodic table, estimating a vast number, N = 10^100, using Stirling's approximation. The significant contribution of semi-empirical parameters such as Gibbs free energy ΔG, enthalpy of mixing ΔHmix, entropy of mixing ΔSmix, atomic size difference Δδ, valence electron concentration VEC, and electronegativity difference Δχ are to predict BCC and/or FCC phases in HEAs. Additive manufacturing facilitates the determination of refractory HEAs systems with the most stable solid-solution and single-phase, and their subsequent hydrogen storage capabilities. Hydride materials, especially those from HEAs manufactured by AM as bulk and solid materials, have great potential for H2 storage, with storage capacities that can be as high as 1.81 wt% of H2 adsorbed for a ZrTiVCrFeNi system. Furthermore, laser metal deposition (LMD) is the most commonly employed technique for fabricating refractory high entropy alloys, surpassing other methods in usage, thus making it particularly suitable for H2 storage.