Mechanical Synthesis and Hydrogen Storage Characterization of MgVCr and MgVTiCrFe High-Entropy Alloy

Body-centered cubic (BCC) and high-entropy alloys are being investigated as potential hydrogen storage materials due to their ability to absorb high amounts of hydrogen at moderate temperatures. Herein, the synthesis and hydrogen storage behavior of new MgVCr BCC and MgTiVCrFe high-entropy alloys are studied. The alloys are initially synthesized by mechanical alloying via high-energy ball milling (HEBM) under hydrogen atmosphere followed by high-pressure torsion (HPT) processing to improve activation. X-ray diffraction (XRD) in combination with transmission electron microscopy (TEM) shows a very refined nanostructure in both samples with the presence of a BCC solid solution phase for MgVCr, whereas the crystalline and amorphous phases coexist in MgTiVCrFe. The MgVCr alloy exhibits fast kinetics but with a low reversible hydrogen storage capacity (up to 0.9 wt%), whereas MgTiVCrFe shows low affinity to absorb hydrogen. Moreover, MgTiVCrFe demonstrates a partial decomposition from the initial structure by hydrogen storage cycling, whereas MgVcr exhibits reasonable stability.