Theoretical Design Of A Series Of 2D TM-C₃N₄ And TM-C₃N₄@Graphene ?TM=V,Nb And Ta? Nanostructures With Highly Efficient Catalytic Activity For The Hydrogen Evolution Reaction

Hydrogen,as a clean and sustainable fuel with a high gravimetric energy density,has been regarded as an ideal substitute for exhaustible fossil fuels and thus meeting the urgent demand for energy and reduced emissions of hazardous substances.The bottleneck we encounter in the hydrogen evolution reaction?HER?is to find a cost-effective catalytic material to reduce the overpotential in the electrolysis process.Superatoms are the stable assembly of atoms that could mimic the chemical behavior of an elemental atom.In addition,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 empolying the concept of the superatom to design new nonprecious catalysts to replace the correlative noble metals?e.g.Pt,the most efficient electrocatalysts for HER?.However,to the best of our knowledge,the related investigations on designing HER catalysts are rather scarce.In this work,we constructing the nonprecious Nb-C₃N₄ configuration that comprising the NbN unit through embedding the transition metal?TM?Nb atom in the in-plane cavity of g-C₃N₄.Through density functional theory?DFT?calculations,we comprehensively investigated the structures and the HER catalytic activity of the Nb-doped g-C₃N₄system.Our computed results reveal that the Nb atom can be stably bonded to the center of the cavity.The calculated adsorption free energy values of H*(?G_H*,a smaller absolute value of?G_H*means a better catalytic activity toward HER)reveal that embedding Nb can significantly improve the catalytic activity for the hydrogen evolution reaction?HER?of g-C₃N₄,since?G_H*value at T_C site is very small with ranging from-0.052 to-0.271 eV.This is mainly due to the NbN-related species can have a similar electronic structure to the noble metal atom?e.g.Pt?,inducing the high HER activity.Besides,the complicated electron transfer process?Nb?N?C?can effectively activate the correlative C atoms in Nb-C₃N₄ to be another factor that leads to good catalytic activity of the system.Similarly,such a high HER activity can also be observed in the analogous V-or Ta-doped g-C₃N₄ systems.In addition,along with the increase of atomic number of the embedded transition metal?TM?,the ionization potential of TM can become lower,and the positive charge on the TM and negative charge on the bonded N atom can also increase.And for these three doped TM-C₃N₄systems,the computed binding energy can exhibit an increasing trend with the increase of the atomic number of TM.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.All these studied systems can uniformly exhibit metallic behavior.Note that good conductivity and high structural stability,which can be beneficial for the HER activity of the material.Thus,all of them can be viewed as a new class of promising candidates as highly efficient and nonprecious electrocatalysts,and this work can also provide new strategies for designing low-cost and high-performance electrocatalysts.