Understanding and unlocking the role of V in boosting the reversible hydrogen storage performance of MgH2

Abstract

Although MgH₂ is widely regarded as one of the most promising solid-state hydrogen storage materials, the high operating temperature and sluggish kinetics of hydrogenation and dehydrogenation are major challenges for its practical application. Herein, V₆O₁₃ nanobelts with a thickness of 11 nm are fabricated to promote the reversible hydrogen storage performance of MgH₂. The favorable interaction between V₆O₁₃ nanobelts and MgH₂ leads to in situ homogeneous formation of metallic V during the initial dehydrogenation of MgH₂. Induced by the catalysis of metallic V, which results in weaker structural stability and higher surface states of MgH₂ attributed to the strong bonding interactions between V and H, the energy required for H₂ desorption from MgH₂ is decreased to 49.5 kJ mol⁻¹, 10.9 kJ mol⁻¹ lower than that of pristine MgH₂. Moreover, during the reversible hydrogenation process, the catalysis of metallic V lowers the energy for H₂ adsorption and dissociation on Mg down to −5.904 and 0.023 eV, respectively, while those values reach −0.086 and 1.103 eV for pristine Mg. As a result, with the introduction of V₆O₁₃ nanobelts with an ultralow content of 3 wt%, a systematic hydrogen storage capacity of 6.8 wt% could be retained at 250 °C after 10 cycles.