Constructing VO/V2O3 interface to enhance hydrogen storage performance of MgH2

Abstract

In this study, MXene-derived V2O5@C nanosheets are successfully synthesized as an efficient catalyst for enhancing the hydrogen storage performance of MgH2. MgH2-V2O5@C exhibits exceptional kinetic and cyclic performance. It desorbs 3.59 wt.% H2 within 120 min at 200 °C and adsorbs 3.9 wt.% H2 within 2.7 h at room temperature after complete dehydrogenation. Moreover, even after 251 cycles at 300 °C, it maintains a hydrogen capacity of 5.45 wt.%, which accounted for 90.5% of the maximum hydrogen capacity. In addition, an activation mechanism for Mg hydrogenation driven by phase transition from V2O3 to VO is firstly clarified through experimental and theoretical analysis. DFT calculations show that the hydrogenation energy barrier of VO (1.01 eV) is significantly lower than that of V2O3 (1.82 eV). The phase transition from V2O3 to VO forms abundant strong hydrogenation sites, effectively reducing the hydrogenation energy barrier of magnesium and activating the hydrogenation ability of deactivated magnesium. Therefore, benefited from the activation mechanism driven by the VO/V2O3 interface, the hydrogen storage capacity of magnesium increased from 4.28 wt.% at 46th cycle to 5.45 wt.% at 251st cycle.