Theoretical Design Of MXene-based Two-dimensional Nitrogen Fixation Electrocatalysts

Finding a technology to replace the Haber-Bosch method is an important topic today,and electrocatalyst nitrogen fixation provides a new idea for this topic.This paper aims to study the potential application of transition metal-modified MXene materials in the field of nitrogen fixation,and to study its catalytic reaction mechanism by analyzing its density of states,calculate its entire nitrogen fixation reaction path,and analyze its feasibility as an electrocatalyst for nitrogen fixation.First,based on first-principles,we explored the feasibility of four transition metals（Fe,Zr,Mo,Ru）intercalated into MXenes material V₂C as an efficient nitrogen reduction reaction（NRR）catalyst.The calculation results show that the overpotential of Mo atom-embedded V₂C under the mixed enzymatic pathway is only 0.49 V.This low overpotential is due to the synergistic effect of the diatomic Mo and V,which makes the nitrogen molecule more easily activated,making its entire NRR.There is no excessive overpotential in the process.In addition,we also investigated the main side reaction of NRR,HER,because the adsorption of nitrogen by Mo/V₂C is significantly larger than that of H⁺,so it can effectively inhibit HER.The extremely low overpotential and good selectivity make Mo/V₂C a potentially feasible catalyst in theory.Secondly,based on first-principles calculations,this work systematically explores the feasibility of diatomic catalysts formed by transition metal dimers（Fe,Mo,Ru）dispersed on2D V₂CN₂ for electrocatalytic nitrogen fixation.The synergistic effect of the diatoms enables better activation of nitrogen and enhanced catalytic performance.The results show that the V₂CN₂ supported double iron atoms（Fe₂@V₂CN₂）have excellent stability,and have obvious advantages in the competition with the HER reaction,which can well inhibit the occurrence of the HER reaction.In the study of the donation-feedback mechanism,the larger charge transfer plays a key role in the activation of nitrogen.Especially in the side-on mode,the overpotential of the enzymatic pathway is only 0.25 e V,which makes Fe₂@V₂CN₂ have better catalytic activity for nitrogen reduction to ammonia.Finally,based on first-principles calculations,other applications of 2D semiconductor energy conversion materials are also investigated.In this paper,the electronic structure and optical properties of the structurally stable Pt SSe/Hf S2 heterostructures are systematically investigated.The results show that the Pt SSe/Hf S₂ heterostructure is a type II heterostructure with an indirect band gap of 1.22 e V.The resulting conduction band offset（CBO）and valence band offset（VBO）are 0.83 and 0.89 e V,respectively.The light absorption coefficient in the visible region reaches 10⁵cm^-1.There is a built-in electric field of 0.58 e V between the heterostructures,which is beneficial to the separation of photogenerated carriers.The band gap can be adjusted regularly by biaxial strain.In particular,the band gap closes at-9%,forming a type III heterojunction.The variation of the heterojunction band gap is related to the unoccupied Hf-5d state.The tunable bandgap under compressive strain suggests that the Pt SSe/Hf S₂heterojunction is a promising candidate material for high-performance tunable optoelectronic nanodevices.Our results can provide some ideas for the design of 2D nitrogen-fixing electrocatalysts and other 2D semiconductor energy conversion materials.