High-capacity and reversible hydrogen storage of two-dimensional V2C and V2CT2 (T = OH, O, F) monolayer MXenes via hybrid adsorption mechanisms

Solid-state hydrogen storage materials offer a promising solution to the compact and safe storage of the hydrogen energy. However, traditional hydrogen storage materials, relying either on chemical adsorption or on physical adsorption, hardly simultaneously meet the technical requirements of high capacity, acceptable operation temperature and pressure, fast kinetics, and good reversibility. Two-dimensional transition metal carbides (MXene) are expected to change this situation due to the hybrid adsorption mechanisms of the Kubas-type interaction, the electrostatic polarization interaction, and weak chemical adsorption. In this work, first-principles calculations were employed to investigate the hydrogen storage performance of the monolayers of V2C MXene and V2CT2 MXene (T = OH, O, and F). Through adsorption energy calculation, charge transfer analysis, the projected density of states (PDOS) analysis, and ab initio molecular dynamic simulations, it is demonstrated that the maximum hydrogen storage capacity of V2C MXene is determined to be 8.146 wt. %, among which the reversible hydrogen storage capacity is 3.258 wt. %, attributed to the contribution of Kubas-type interactions. In addition, the effects of –O, –F, and –OH functional groups on the hydrogen storage performance were further studied. Specifically, V2C(OH)2 is suitable for hydrogen storage with a reversible hydrogen storage capacity of 2.59 wt. %. This work provides an important reference for understanding the hydrogen storage properties and mechanisms of V2C and V2CT2 MXene.