Study Of Carbon-based And Its Composite Materials In The Field Of Electrocatalytic Nitrogen Reduction

Ammonia（NH₃）,as the most basic raw material chemical,has become indispensable in industrial production,energy economy and other fields.However,the industry now mainly relies on the Haber-Bosch process to convert chemical fuels and nitrogen（N₂）in the air into ammonia.This method requires the participation of iron-based catalysts under high temperature and pressure conditions.As a result,energy use accounts for 2%of the world’s total energy consumption and annual carbon dioxide emissions account for about 1%of global greenhouse gas emissions.This is obviously in conflict with the“Carbon-peak”and“Carbon-neutral”work proposed by the Chinese government.Therefore,it is more urgent to find a new method of NH₃synthesis which is both economical and sustainable.Electrocatalytic nitrogen reduction reaction（ENRR）is an alternative method for NH₃ synthesis due to its high efficiency,controllable selectivity and simple reaction unit.However,efficient electrocatalysts are needed to deal with the challenge of breaking the N≡N triple bond.In order to find a low-cost,earth-abundant,environmental-friendly materials as ENRR catalyst,this paper carried out related research.Since carbon-based materials conform to the above characteristics and have shown unique advantages in other electrocatalysis fields,this paper starts from the study of carbon-based materials,and then uses the carbon-based materials with many characteristics to form new composites with the reported catalysts to study the performance of ENRR.Some excellent research results have been achieved by using heteroatom-doped carbon as a new type of electrocatalyst for basic electrochemical reactions.In this paper,nitrogen doped carbon fibers（N-CF）were synthesized by electrospinning technology and applied in the field of ENRR.The final electrochemical performance test results show that in 0.1 M HCl the optimum NH₃ yield of N-CF can reach 14.89μg h^-1mg^-1_cat.at-0.45 V vs.RHE,and the maximum Faradaic efficiency can reach 2.66%at the potential of-0.35 V vs.RHE.Meanwhile,the N-CF has good stability and selectivity.Due to the adjustable advantages of biological carbon in surface area,porosity,surface charge and element content,on the basis of previous experimental conditions,carbon nanosheets（CN）were obtained by annealing tannic acid.After ENRR tests were carried out in 0.1 M HCl and 0.1 M Na₂SO₄,it was found that CN has better electrochemical performance in acidic conditions.At-0.6 V vs.RHE,the performance is the best:NH₃ yield is 20.15 20.15μg h^-1mg^-1_cat.,and Faradaic efficiency is 4.97%.At the same time,the catalyst also shows good electrochemical durability.Mn₃O₄ nanocube has been proved to be an effective catalyst for ENRR,and the electrical conductivity of Mn₃O₄ can be effectively improved by using rGO.In this paper,Mn₃O₄/rGO composite material was synthesized by hydrothermal method and applied in the field of ENRR.The results show that NH₃ yield rate and Faradaic efficiency can reach 17.4μg h^-1mg^-1_cat.and 3.52%respectively in 0.1 M Na₂SO₄ at-0.85 V vs.RHE.Moreover,it also shows high electrochemical stability and selectivity in the electrolysis process.The research also further reveals that the rGO can effectively improve the conductivity of the material,increase the BET area,and expose more active area.Finally,the density functional theory calculation shows that the catalytic active crystal plane of the material is the（1 1 2）planes of Mn₃O₄.