Study On The Preparation And Electrocatalytic Nitrogen Reduction Properties Of MXene-based Composites

As the most widely used method for the synthesis of ammonia in the industry,the Haber-Bosch process consumes a large amount of energy and generates a large amount of CO₂.The electrocatalytic nitrogen reduction reaction（NRR）ammonia synthesis method is a more environmentally friendly method and can effectively reduce the use of fossil fuels,which has attracted more and more attention from researchers.Although some progress has been made in this field,there is still a great need to design electrocatalysts that can achieve both high ammonia yield and high Faradaic efficiency for NRR.The two-dimensional MXene material Ti₃C₂ has a unique structure and excellent electrochemical performance,and is expected to become a high-performance catalyst for electrocatalytic ammonia synthesis.Ti₃C₂ is synthesized by selective etching of MAX phase material Ti₃AlC₂ to remove Al.However,high-purity Ti₃AlC₂ usually needs to be synthesized under high temperature conditions,which results in a large amount of energy consumption while causing higher production costs.Therefore,there is an urgent need to find a new method that can effectively reduce the synthesis temperature of MAX phase Ti₃AlC₂.In this study,we used a NaCl-assisted method to synthesize Ti₃AlC₂ and etch it to obtain Ti₃C₂.Cu/Ti₃C₂ and CuAg/Ti₃C₂ composites were synthesized based on Ti₃C₂ and used as catalysts for the electrochemical synthesis of ammonia.First,Ti₂AlC and TiC were mixed in a 1:1 M ratio by ball-milling,and the fully mixed Ti₂AlC-TiC mixture was completely coated with NaCl and placed in a corundum boat.The corundum boat was put into a tube furnace,and the synthesis reaction was carried out at a temperature of 1150°C in an argon atmosphere.The results of material characterization and theoretical calculation simulation confirmed the successful synthesis of high-purity Ti₃AlC₂with ideal crystal structure and the subsequent successful preparation of Ti₃C₂.This molten-salt-assisted method can successfully reduce the synthesis temperature of MAX phase Ti₃AlC₂ by 200°C.It has more advantages in energy and material costs,and is expected to promote the application and development of two-dimensional MXene materials.Based on the preparation of two-dimensional MXene material at low temperature,a Cu/Ti₃C₂ composite material was synthesized and tested for NRR.It was found that the material can electrochemically reduce nitrogen to ammonia with good selectivity under ambient conditions.When the NRR test was performed in a 0.1 M KOH solution,at a potential of-0.5 V,the ammonia production rate can reach 3.04μmol cm^-2 h^-1,and the Faradaic efficiency can reach 7.31%.It is worth noting that the Cu/Ti₃C₂ composite material exhibits strong electrochemical stability during the NRR process,and is expected to be used in the electrochemical synthesis of ammonia.In order to further improve the catalytic performance of the Cu/Ti₃C₂ composite material,CuAg/Ti₃C₂ composite materials were synthesized based on Ti₃C₂.The CuAg/Ti₃C₂ catalyst has better activity in NRR test at room temperature and pressure.When measured in 0.1 M KOH,at a potential of-0.5 V,the ammonia production rate and Faradaic efficiency of the catalyst were as high as 4.12μmol cm^-2 h^-1 and 9.77%,respectively.Compared with other reported two-dimensional nitrogen reduction electrocatalysts,the catalyst has excellent stability and selectivity.Theoretical calculation results show that the synergistic effect in the composite material enhances its catalytic activity.