Catalytically driven hydrogen storage in magnesium hydride through its chemical interaction with the additive vanadium

Considering the importance of understanding the catalysis of metal oxides incorporated hydrogen storage system MgH2, in this study we tried to identify the chemical interaction between magnesium hydride (MgH2) and the additive vanadium pentoxide (V2O5). Two test samples, MgH2+0.25V2O5 and 0.25MgH2+V2O5, were subjected to mechanical milling treatment for different times (15 min, 1h, 2h, 5h, 10h and 15h), and the phase change was monitored systematically. The detailed X ray diffraction analyses suggest that the phase evolution starts with the reduction of V2O5 and it ends up with the formation of a rock salt structure, typified by MgxVyOx + y. High-resolution transmission electron microscopy study coupled with energy dispersive spectroscopy suggest that the distribution of V, Mg and O in MgxVyOx + y is homogenous, though V-rich spots/boundaries can be spotted across the rock salt particles. Further verification by X–ray photoelectron spectroscopy suggests that V exists in a mixed valence state in the end sample, 15h reacted MgH2+0.25V2O5. Differential scanning calorimetry and hydrogen storage kinetics studies prove the improved hydrogen storage behavior of MgxVyOx + y containing MgH2 sample. We believe that the formation of MgxVyOx + y rock salt particles with V enriched spots/interfaces is the key step in the catalysis of V2O5 incorporated hydrogen storage system, MgH2.