Study On Preparation Of Transition Metal Sulfide Composite Material And Its Electrocatalytic Nitrogen Fixation Performance

Ammonia is a widely used chemical raw material and a promising clean energy.At present,the primary NH₃production way depends on industrial synthetic ammonia（Haber-Bosch）,which consumes high energy and emits large carbon emissions.In order to reduce emissions,save energy,and achieve sustainable environmental protection development,it is urgent to explore a new alternative synthetic ammonia technology with lower energy consumption and green environmental protection.Because electrocatalytic ammonia synthesis has the advantages of simple process,safe,controllable and mild conditions,it is favored by the majority of scientific researchers.However,electrocatalytic nitrogen fixation still has the problem of slow ammonia production rate and low Faraday efficiency,so it is of great significance to explore a new type of stable,efficient and high-yield electrocatalytic nitrogen fixation catalyst.In response to the above problems,this article designed and synthesized an electrocatalytic nitrogen fixation catalyst with better performance through morphology control,heterostructure building and defect engineering.The main research contents are as follows:1.The heterostructure of cobalt-molybdenum bimetallic sulfide was constructed and its nitrogen fixation reaction path was clarified.Using polyoxometalate as the precursor,Co S₂/Mo S₂ with a heterojunction structure was synthesized by a one-step hydrothermal method.Co S₂/Mo S₂ formed a flower-like array structure from interlaced nanosheets.The synergistic effect between Co S₂ and Mo S₂ components and the formation of mesoporous structure improve the charge transfer characteristics,increase the number of electrocatalytic active sites and electrochemical active area,and then improve the electrochemical performance of Co S₂/Mo S₂.The Co S₂/Mo S₂ hybrid exhibited a greatly enhanced NRR performance,whether NH₃ yield(38.61μg h^–1mg^–_cat.~1)or FE（34.66%）in acidic K₂SO₄（p H=3.5）solution under ambient conditions.This study successfully designed and constructed high-efficiency transition metal sulfide catalysts for electrocatalytic nitrogen fixation,and promoted the development and practice of transition metal sulfide catalysts in this field.2.Through the introduction of sulfur vacancies,the core-shell cobalt tungsten sulfide in electron deficient environment was formed,and its electrocatalytic nitrogen fixation performance was studied.Using the prepared ZIF-67@PW₁₂ as the precursor,the Co₉S₈@WS₂ with S vacancies was formed by calcination and vulcanization at high temperature.The nanosheet structure increases the specific surface area of the composite,which is conducive to the infiltration and penetration of the electrolyte.The combination of the Co₉S₈ core with excellent redox ability and the outer layer WS₂ with good stability can improve the electrocatalytic performance and stability of the composite material.The introduction of S defects adjusts the electronic structure of the material,reduces the reaction energy barrier,makes nitrogen molecules better adsorbed and activated,and promotes the electrocatalytic nitrogen fixation performance.The Co₉S₈@WS₂ hybrid exhibited a greatly enhanced NRR performance,whether NH₃ yield(50.25μg h^–1mg^–1_cat.)or FE（46.81%）at–0.4V vs.RHE in 0.1 mol L^–1KOH solution under ambient conditions.This experiment provides a new idea for the design and preparation of polyacid and metal organic framework derived nano materials as high-efficiency nitrogen fixation electrocatalysts.