Preparation Of Molybdenum Disulfide-based Electrocatalyst And Study Of Electrocatalytic Nitrogen Fixation Properties

Ammonia（NH₃）is an important chemical raw material,widely used in chemical production.Electrochemical synthesis of ammonia in aqueous solution by electric energy is a promising method.But the ammonia yield of electrochemical ammonia synthesis are low,so clean and efficient catalysts are needed to improve the ammonia yield of electrochemical ammonia synthesis.Based on the defect engineering and electronic structure of molybdenum disulfide,the modification of molybdenum disulfide by doping metal and nonmetal has significantly improved its ammonia yield of electrocatalytic ammonia synthesis in aqueous solution.The main research contents are as follows:（1）Boron doped molybdenum disulfide was synthesized by using ammonium molybdate tetrahydrate as molybdenum source,boron trioxide as boron source and thiourea as sulfur source in N₂atmosphere and calcined at 700℃for 2 h.In acidic electrolyte(0.005 mol·L^-1dilute sulfuric acid)under environmental conditions,when the potential is-0.5 V（vs.RHE）,the boron doped molybdenum disulfide achieves the highest ammonia yield(53.73μg _NH3·h^-1·mg^-_{ca t}~1)and Faraday efficiency（2.33%）,and the ammonia yield is 5.47 times that of molybdenum disulfide under the same potential.The improvement of ammonia yield of boron doped molybdenum disulfide electrocatalytic ammonia synthesis is attributed to the successful doping of boron.When boron atoms are introduced into molybdenum disulfide,the boron atoms and molybdenum atoms form a strong-weak electron polarization pair due to the great difference in electronic properties.When the electron polarization pair acts as the active center of ammonia electrocatalytic synthesis,it can weaken the nitrogen-nitrogen triple bond of nitrogen and promote the polarization and the first protonation of nitrogen,thus improving the ammonia yield of ammonia electrocatalytic synthesis.（2）Molybdenum disulfide co-doped with nickel and phosphorus was synthesized by hydrothermal method using thioacetamide as sulfur source,sodium molybdate dihydrate as molybdenum source,sodium hypophosphite monohydrate as phosphorus source and nickel acetate tetrahydrate as nickel source.In acidic electrolyte(0.005 mol·L^-1dilute sulfuric acid)under environmental conditions,when the potential is-0.5 V（vs.RHE）,the ammonia yield of the electrocatalytic synthesis of ammonia by nickel and phosphorus co-doped molybdenum disulfide is 84.29μg _NH3·h^-1·mg_c^-1_at,and the Faraday efficiency is 2.39%.The ammonia yield is3.67 times that of nickel doped molybdenum disulfide at the same potential.It is 4.35 times of molybdenum disulfide at the same potential.The experimental results show that the introduction of nickel partially converts the 2H phase molybdenum disulfide with semiconductor properties into 1T phase molybdenum disulfide with metal properties,which improves the conductivity of molybdenum disulfide;and the introduction of phosphorus increases the number of sulfur vacancies in molybdenum disulfide,thus increases the concentration of^*H,promotes the protonation of nitrogen,and improves the ammonia yield of electrocatalytic ammonia synthesis.