Study On The Application Of Multi-metal Sulfides In Electrocatalytic Nitrogen Reduction Reactions

Against the backdrop of global low-carbon transition,the emerging low-carbon technology for synthetic ammonia has aroused widespread attention.With the advantages of high energy density and easy storage and transportation,ammonia（NH₃）is becoming an important carrier for hydrogen energy utilization in the context of carbon neutrality.In addition,ammonia offers a wide range of applications in agriculture,pharmaceuticals and transportation.At present,the traditional Harber-Bosch（H-B）process dominates the production of industrial grade ammonia,which is based on the synthesis of ammonia from nitrogen and hydrogen under high temperature and pressure conditions.This process has low utilization rate,harsh preparation conditions,and a large amount of CO₂ gas during the synthesis process,which aggravates the greenhouse effect and brings environmental problems.Therefore,there are two solutions to the problems caused by the H-B method.One is to design an efficient catalyst that reduces the reaction conditions of the traditional synthesis technology.The other is to develop an environmentally friendly and sustainable ammonia synthesis method that avoids the environmental problems caused by harsh reaction conditions.Electrocatalytic nitrogen fixation is considered as a promising ammonia synthesis technology,which uses nitrogen and water as raw materials and electrical energy as driving force to synthesize ammonia in the presence of an electrocatalyst.The technology provides mild reaction conditions,low energy consumption,and no greenhouse gases or other harmful gases.Electrocatalytic nitrogen reduction is a promising green generation pathway in this"dual-carbon"context.Multi-metal sulfides are characterized by good electrical conductivity,electrochemical activity,complex and variable chemical composition and metal valence states.Compared with mono-metallic sulfides,multi-metal sulfides present more tunability properties.The control of material morphology and properties can be achieved by regulating the ratio of their elemental composition to expose more catalytic active sites,thus improving the performance of e-NRR.Therefore,the different active sites of multi-metals and the synergistic effects of metals are exploited.The design and development of efficient catalysts that can promote the activation of N₂ molecules and improve the reaction kinetics is the key to improve the nitrogen reduction performance.The thesis focuses on the preparation of multi-metal sulfide catalytic materials.The performance of e-NRR is investigated by preparing nano-catalytic materials through the construction of heterogeneous interfaces or defective structures.Combined with the physical characterization and electrochemical performance study analysis,the conformational relationship between multi-metal sulfides and the performance of e-NRR was explored.The specific study contents are as follows:（1）Firstly,Cu Co₂S₄ and its composite material Cu Co₂S₄@Cu S were grown directly on copper foam using hydrothermal method with copper foam as the substrate.The composites exhibited relatively excellent catalytic performance for e-NRR ammonia synthesis applications.Its faraday efficiency could reach 10.37%at-0.3 V vs.RHE,which is 2.7 times higher than that of Cu Co₂S₄.The excellent catalytic performance was attributed to the construction of heterogeneous interface that modulated the electronic structure of the electrocatalyst and redistributed the charge,and the tight coupling of the interface between Cu Co₂S₄ and Cu S also enhanced the electron transport,thus improving the electrocatalytic activity.（2）FeCo dihydroxide was prepared by the solvothermal method and FeCo₂S₄was obtained after sulfidation.Based on this,catalytic materials with defective structures（Mo-FCS）were further synthesized by regulating the doping amount of Mo in FeCo₂S₄.Among them,5%Mo-doped FeCo₂S₄ had more excellent catalytic performance,and the faraday efficiency of 5%Mo-FeCo₂S₄could reach 15.84%at-0.2 V vs.RHE.The 5%Mo-FCS material was proved to be a better electrocatalyst with high selectivity and good stability.Combined with physical characterization and electrochemical analysis tests,it was shown that the doping of Mo modulated the electronic structure of FeCo₂S₄,improved the electron transfer rate and accelerated the kinetics of the nitrogen reduction reaction,which was beneficial to the performance of e-NRR.