▎ 摘　　要

Inspired by the fascinating result that NbN-related species can possess a similar electronic structure to noble metal atoms (e.g. Pt), in this work we have proposed for the first time a new strategy, through embedding the transition metal (TM) Nb atom in the in-plane cavity of g-C3N4, for constructing the nonprecious Nb-C3N4 configuration comprising the NbN unit exhibiting noble-metal-like characteristics. Our computed results reveal that embedding Nb can significantly improve the catalytic activity for the hydrogen evolution reaction (HER) of g-C3N4, and even that the formed Nb-C3N4 can exhibit a considerably high HER catalytic activity over a wide range of hydrogen coverage. Similarly, such a high HER activity can also be observed in the analogous V- or Ta-doped g-C3N4 systems. Furthermore, a series of new hybrid systems TM-C3N4@G (TM = V, Nb or Ta) is constructed by coupling the single-layered TM-C3N4 with graphene, and all of them can also possess a considerably high HER catalytic activity over a wide range of hydrogen coverage. Moreover, all these composite TM-C3N4 and TM-C3N4@G systems possess high structural stability and metallic conductivity. Thus, all of them can be viewed as a new class of promising HER catalysts, and this work can also provide new strategies for designing low-cost and high-performance electrocatalysts.