Experimental Preparation And Properties Research Of Vanadium-Based Electrocatalytic Nitrogen Fixation Materials

NH₃ plays a decisive role in both agricultural and industrial products.Meanwhile,it provides us with an attractive energy carrier with high hydrogen density and low liquefying pressure.As the primary process for industrial-scale NH₃ production,the Haber-Bosch（H-B）process however operates under harsh conditions（Pressure:200-350 atm;Temperature:400℃～650℃）,leading to large energy consumption and heavy CO₂ emission.Facing the problems of the century,such as energy crisis and global warming,it is urgent to develop an alternative method of carbon neutral ammonia synthesis,which the electrochemical reduction of N₂ using water as a media source.But it relies on highly active and stable catalysts.Therefore,it is essential to seek electrocatalysts with higher NH₃ yield rate and Faradaic efficiency（FE）,good stability and excellent selectivity.In this work,Firstly,P-V₂O₃/C nanorods were prepared by the heteroatom doping modification of V₂O₃/C by calcination of Na H₂PO₂,and the introduction of P with rich valence electrons into V₂O₃/C crystals.And it has good nitrogen reduction（NRR）activity.In the electrolyte of 0.1 mol/L Na2SO4,the NH₃ yield increased from12.6μg h^-1 mg^-1_cat.to 22.4μg h^-1 mg^-1_cat.,at–0.25 V vs.reversible hydrogen electrode（RHE）;Faraday efficiency（FE）increases from 6.06%to 13.78%at–0.25 V vs.RHE.Importantly,the catalyst has high electrochemical durability and outstanding selectivity.Then,the NRR reaction mechanism of N₂molecule on V₂O₃/C（104）surface was studied by density functional theory（DFT）calculation.The active sites and corresponding changes of electronic structure on the surface of NRR P-V₂O₃/C electrocatalyst were analyzed from the microscopic level to further understand the origin of NRR catalyst activity.The DFT results show that P doping causes geometric and electronic structure changes near（104）surface,including crystal distortion,bond length,bond angle and charge distribution changes.It is confirmed that the presence of P can expose more active sites of nitrogen reduction on the surface.Enhance the adsorption of nitrogen on V₂O₃ surface,which is conducive to the reduction of nitrogen to produce ammonia.Finally,a two-dimension electrocatalyst for V₂O₅ nanosheets was prepared by cryogel method and further calcination.The catalyst has good nitrogen reduction activity,in 0.1 mol/L Na₂SO₄ electrolyte,the NH₃ yield can be as high as 19.5μg h^-1mg^-1_cat.（at–0.25 V vs.RHE）;FE is 10.08%（at–0.15 V vs.RHE）.This performance is better than most reported NRR catalysts.Through durability test,it is found that it has good electrochemical stability and NRR selectivity.