The effects of Al on the hydrogen storage properties of V from first-principles calculations

Vanadium-based materials have great potential for advancing novel hydrogen storage technology. To address the limited gravimetric hydrogen storage capacity of V, incorporating light alloying elements has been proposed. In this study, the hydrogen storage capacities of V_1-Al (x = 0, 0.1, 0.2, 0.3, and 0.4) solid solutions are investigated by employing first-principles calculations. Our results indicate that both the stability and hydrogen storage capacity of V_1-Al hydrides decrease with an increase in Al content due to a reduction of chemical contribution, consistent with experimental results. The chemical bond analysis, Bader charge, and projected density of states investigation reveal that the Al-H antibonding states appear at the Fermi level and net H-H antibonding states surrounding Al form due to the transfer of excessive electrons from Al to H. To further explore the relationship between chemical bonding and desorption enthalpy, over 20 face-centered cubic (FCC) metal dihydrides are selected. It is found that the desorption enthalpies correlate weakly with the metal-hydrogen (M-H) bond strength and positively with M-H antibonding states below the Fermi level. Our study reveals the mechanism of interactions between chemical bonds and hydrogen storage properties in metal hydrides, providing valuable insights for the future design of hydrogen storage materials.