Performance And Mechanism Of Surface Defect Engineering Of Two-Dimensional Materials In Electrocatalytic Nitrogen Reduction Reaction

Ammonia（NH₃）is widely used in the manufacture of modern fertilizers,plastics,fibers,explosives and other chemical products.However,the current industrial production of NH₃ is limited to the traditional Haber-Bosch process.In recent years,electrocatalytic nitrogen reduction（N₂）has been widely studied as a green and clean method for NH₃ production..At present,various types of catalysts have been developed and used for electrochemical nitrogen reduction reaction（E-NRR）.To achieve high catalytic performance and high selectivity simultaneously,electrocatalysts must be rationally designed to optimize mass transfer,chemical（physical）adsorption,and transfer of protons and electrons.In this paper,the reaction mechanism of E-NRR is discussed in detail,referring to the latest research progress in this field,summarizing the existing problems in the current research,and putting forward a reasonable prospect for the future research work.Here,we completed the study of defect engineering on two 2D materials to enhance the catalytic performance of the material E-NRR,and discussed the reaction mechanism in depth.The specific research contents are as follows:1.By in situ oxidation of Nb₂CT_x MXenes,Nb₂O₅ nanoparticles（NPs）intercalated Nb₂CT_x MXenes 2D material,namely Nb₂O₅/C,was synthesized and used as a cathode catalyst material for E-NRR.Density functional theory（DFT）was used for theoretical calculations to explore active sites and reaction mechanisms.The first step should be N₂adsorption on an oxygen vacancy with an end-on configuration,and the potential determining step（PDS）might be the first hydrogenation step.The catalysts were composed of a few layers of graphitic carbon with intercalated Nb₂O₅ NPs,which resulted in the activation of Nb layers for NRR and opening of the interlayer space for N₂transport.Notably,controlled oxidation produced plenty of V_O which were the active sites for NRR.The experimental results found,Nb₂O₅/C-800 obtained a high FE of 11.5%at-0.4 V vs reversible hydrogen electrode（RHE）under ambient conditions.At the same time its ammonia production(V_NH3)was 29.1μg h^-1 mg^-1_cat.This high FE indicated the great selectivity of this catalyst for NRR,outperforming recently reported Nb-based catalysts and some other catalysts.Furthermore,the catalyst showed great stability after longtime electrochemical tests.2.Multidefective boron nitride nanosheets（C-BNNSs）for catalyzing efficient E-NRR were synthesized using a template method.Specifically,for electrocatalytic NRR,the C-BNNSs prepared by this method has two advantages compared with previous studies.First,the C-BN was grown on the surface of the porous template and could achieve the sheet-like structure with a large pore volume.This led to a number of unsaturated boron atoms along the edge of the pores,which could act as chemically reactive sites for NRR.Second,doping of carbon atoms could improve the electronic conductivity of C-BNNSs compared with pure BNNSs,leading to a faster charge transfer rate that would promote electrocatalysis.To be used as the cathodic catalyst for NRR,C-BNNSs achieved a high V_NH3 of 36.7μg h^-1 mg^-1_cat and a comparable FE of 6.51%at-0.55 V（vs.RHE）in 0.1 M HCl solution.In conclusion,we have carried out surface modification of 2D materials MXenes and BNNSs by defect engineering to realize the surface activation of the materials and greatly improve the E-NRR performance of such materials.Defective sites in electrochemical catalysts often have unique electronic structures that can be appropriately combined with reaction intermediates to provide enhanced activity and improve reaction selectivity.In addition,through theoretical calculations,we deeply explored the reaction mechanism of E-NRR under the action of catalysts,which provided a solid theoretical basis for the improvement of material properties.