Research On The Preparation And Application In Electrochemical Synthesis Ammonia Of Nano-metal Carbides

Industrial ammonia?NH₃?production is mainly dominated by Haber-Bosch processing,which usually requires high temperature and high pressure,consuming a large amount of energy producing a large amount of CO₂ emissions.NH₃ production by electrochemical reduction of N₂?NRR?at room temperature and pressure is considered to be a promising alternative to Haber-Bosch reaction,which uses water as hydrogen source and has no carbon emission as a clean and sustainable means of NH₃ production.However,achieving both high NH₃ yield and selectivity is still a great challenge for NRR,which requires electrocatalysts with high activity to break stable N?N bond.Transition metal carbides?TMCs?have great potential in electrocatalysis due to their high conductivity and unique electronic structure.However,studies on transition metal carbides?TMCs?as NRR electrocatalysts are very limited.Herein,we prepared TMCs based nano-electrocatalyst and study its NRR catalytic characteristics in detail with complete electrochemical tests,also further explained its possible NRR mechanism via density functional theory?DFT?.The specific research content can be divided into the following three parts:?1?The two-dimensional vanadium carbide?V₂C MXene?was prepared by chemical etching and the structure and composition are fully characterized.Then series tests were conducted to test its NRR performance.The ammonia yield and Faraday efficiency?FE?in 0.1 M Na₂SO₄ are 12.64?g h^-1 mg^-1_cat.and 4.02%,respectively,with no significant performance degradation after five cycles.Therefore,the layered structure of V₂C nano-sheets can be potentially used as NRR catalyst,which lays a foundation for the subsequent design of efficient and stable two-dimensional NRR electrocatalyst.?2?Titanium carbide/carbon nanofibers?TiC/C NFs?are designed and prepared.Meanwhile,complete characterization analysis was also carried on.After tested in acidic,neutral and alkaline electrolytes,it was found such electrocatalyst achieves a large NH₃ yield of 14.1?g h^-1 mg^-1_cat.and a high FE of 5.8%in 0.1 M HCl.Through a series of control tests,it was found that its excellent electrocatalytic performance was mainly due to the synergistic effect of self-generated TiC nanocrystalline and one-dimensional carbon framework,in which TiC nanocrystalline has a strong adsorption of N₂ which would facilitates cleavage of N?N bond and carbon fiber skeleton increase conductivity and active sites.DFT results show that TiC can efficiently activate N₂ in enzymatic route with a reaction barrier of only 0.88 eV.?3?Chromium carbide nanoparticle embedded carbon nanofibers?Cr₃C₂@C NFs?are designed and prepared as NRR electrocatalyst.When tested in 0.1 M HCl,it acheives a high FE of 8.6%and a large NH₃ yield of 23.9?g h^-1 mg^-1_cat.,superior to most of the well-developed NRR electrocatalysts in an ambient environment.In addition,it was found to have good electrochemical and structural stability during 24 h long-term test.The DFT calculation shows that the reaction barrier of NRR on the surface of Cr₃C₂ is only 0.53 eV.The conclusion demonstrated that TMCs own high catalytic activity as well as stability towards NRR.Meanwhile,TMC/C composite 1-D structure cans significantly promote NRR process.Such conclusion is helpful for the design and preparation of efficient NRR electrocatalysis,.