Revealing the effect of 2D carbides with different metal sites for improving hydrogen storage in MgH₂

Two-dimensional (2D) carbon materials are considered as efficient catalysts for improving hydrogen storage in MgH₂, but their catalytic mechanisms of different materials remain unclear. Herein we compare the hydrogen storage properties of MgH₂ with doping different 2D carbon materials for revealing their catalytic effecting mechanisms. It can be seen that the effect of 2D metal carbides including Nb₂C and Ti₂C are superior to 2D graphene for improving hydrogen storage properties of MgH₂, where the Ti₂C exhibits the best catalytic effect with a remarkable decrease of activation energy (E _a) from ∼124 kJ/mol for doping graphene to ∼86 kJ/mol. This is related to the changes of individual metal and graphite chemical valence states of catalysts. The high catalytic activity of the hydrogen storage reaction originates from its unique layered structure and in situ formation of MH_X, i.e., the tiny metal crystals can serve as a channel to facilitate hydrogen transport in MgH₂ matrix. Moreover, the Ti catalytic effect is better than Nb, which originates from the surface of the multivalent Ti atoms is an intermediate of the electron moving between H^- and Mg²⁺, thus leading to the Ti₂C catalyzed MgH₂ with superior hydrogen kinetic and cyclic performance.