Design,Preparation And Electrocatalytic Performance Of Novel 2D-COFs

In this paper,the first-principles density functional theory?DFT?method is used to theoretically controllably design a novel phenazine-linked two-dimensional covalent organic framework material?2D-COFs?with excellent performance of electrocatalytic oxygen evolution?OER?.Next,the preparation,structure analysis and performance research of the 2D-COFs were carried out experimentally to verify the correctness of the theoretical driver.Finally,combining theory with experiment,the excellent electrocatalytic OER performance of the 2D-COFs is explained in depth from the nature of the microstructure that affects the function.First,based on the first-principles DFT,the band structures tuning of h-C₂N and h-C₅N₂ using the SIESTA software package.The geometric structure and electronic properties of 2D porous graphene sheet structures h-C₂N and h-C₅N₂ with specific CN stoichiometric ratios,both of which are semiconductors with direct band gaps,were calculated.We also constructed defect structures for h-C₂N and h-C₅N₂ and found that the defect structures h-C₂N-d and h-C₅N₂-d are N-type semiconductors with two intermediate doped bands that can trap electrons.h-C₂N and h-C₅N₂ sheets were tailored to one-dimensional nanoribbon A-h-C₂N,A-h-C₅N₂,Z-h-C₂N and Z-h-C₅N₂,which showed larger bandgap and higher lowest conduction band?CBM?positions than the corresponding h-C₂N and h-C₅N₂.The band gap decreases with increasing pore size,regardless of the size and chirality of the nanoribbons.As the width of the nanoribbon increases,the band gap decreases and approaches the corresponding 2D sheets.The band structures characteristics of the above h-C₂N and h-C₅N₂ and their defective derivatives are summarized,and their catalytic properties are predicted.According to this idea,we designed a new 2D-COFs?COF-C₄N?with the same phenazine connection as h-C₂N and h-C₅N₂,but with a pore size between the above two,with a CN stoichiometric ratio of 4:1.Next,the band structures of the series h-C₂N,COF-C₄N and h-C₅N₂ were calculated and summarized using two methods,GGA/PBE and HSE06,and their potential OER performance was found.At the same time,based on the hybrid DFT calculations using the Gaussian 09 program,at the level of B3LYP/6-31+G?d?,the OH*,O*,and OOH*free energies of the model intermediates in the OER pathway were calculated,and conducted a theoretical electrocatalytic OER performance study,and the results show that COF-C₄N has potential OER performance.Based on the theoretical study of DFT,this novel type of 2D-COFs was successfully synthesized.We conducted a series of structural tests on the experimentally prepared COF-C₄N to prove that COF-C₄N is a phenazine-linked porous graphene rigid planar crystal structure,which is consistent with the theoretically designed structure.The low overpotential of 349 mv@10 m A cm^-2 and the Tafel slope of 64 m V dec^-1 were obtained by analyzing the results of the electrocatalytic OER performance test of COF-C₄N to verify the theoretical prediction.The free energy of OH*,O*and OOH*of the model structure in the OER pathway at an applied bias of 1.579 V are calculated,and it was found that the OER pathway showed a reasonable downhill trend at U=1.579 V,which further explained the excellent performance of the COF-C₄N electrocatalytic OER.