Abstract
Two-dimensional (2D) carbon materials are considered as efficient catalysts for improving hydrogen storage in MgH(2), but their catalytic mechanisms of different materials remain unclear. Herein we compare the hydrogen storage properties of MgH(2) with doping different 2D carbon materials for revealing their catalytic effecting mechanisms. It can be seen that the effect of 2D metal carbides including Nb(2)C and Ti(2)C are superior to 2D graphene for improving hydrogen storage properties of MgH(2), where the Ti(2)C 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 MgH(2) 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 Mg(2+), thus leading to the Ti(2)C catalyzed MgH(2) with superior hydrogen kinetic and cyclic performance.