EDS maps before and after H 2 cycling are also shown in Figure . Polished surfaces were not possible due to powder form of the HEAs upon hydrogenation; regardless, no phase segregration was noticeable in the EDS maps for any of the compositions. EDS spectra supporting near-equimolar elemental compositions are shown in the SI. The bottom of Figure shows PCT curves for each composition, with an inset corresponding to the van't Hoff analysis from which thermodynamic parameters can be derived. Table summarizes the ML predictions vs. experiment for the Pareto axis quantities visualized in Figure . The ML model predicts a ∆H ranking of MgTiVZrNbHf > Mg-TiVCrNb > MgAlTiVCr, and the significant destabilization of MgAlTiVCr relative to Mg-TiVZrNbHf is correctly captured. The model also correctly predicts the effects of Mg addition on ∆H and H/M relative to the non-Mg containing HEAs. The saturation capacity H/M, which was extracted from the last PCT measurement point, is underestimated for MgAl-TiVCr in Table (in contrast to MgTiVZrNbHf which has clearly reached saturation). Due to sluggish kinetics observed in the MgTiVCrNb sample and the highly sloped plateau, saturation of the material has not occurred despite the maximum pressure (100 bar) and high measurement temperature (644 K). Thus, obtaining equilibrium during PCT measurements at lower temperatures was not possible in a reasonable time period. Therefore, future investigation of this material should consider yet additional substitution strategies that improve kinetics so that equilibrated PCT can be obtained at lower temperature, and both reaction thermodynamics and saturation capacity can be accurately obtained.