Controllable Preparation Of Metal Sulfide Cathodes And Investigation On Their Eletrocatalytic Nitrogen Fixation Performance

Ammonia plays an important role in production and life.It can not only be widely used as a raw material for the production of fertilizers,resins,rubbers,etc.,but also be used as a new type of carbon-free clean fuel due to its large hydrogen content of 17.6 wt%and high energy density of4.3 k Wh kg^-1.However,the traditional Haber-Bosch method（N₂+3 H₂→2 NH₃）for the ammonia synthesis needs to be completed at a high temperature and pressure of 400–500 ^oC and150–250 atm,which has extremely high requirements for production equipment and requires fossil fuels,which results in a large amount of greenhouse gases.CO₂emissions and waste of resources make it increasingly important to develop sustainable ammonia synthesis methods.Among many methods,electrocatalytic nitrogen fixation can be performed at normal temperature and pressure,which has the advantages of environmental protection and energy saving,and has attracted widespread attention.At present,there are some new catalysts for electrocatalytic nitrogen fixation,such as noble metal catalysts,carbon-based catalysts,and non-noble metal-based catalysts.Recently,low cost and rich content nanostructures of abundant metal oxides,sulfides,nitrides and carbides have been discovered.In these materials,metal sulfides have the advantages of easy synthesis and good activity,due to their strong agglomeration tendency and poor carrier mobility,they have low Faraday efficiency and ammonia yield.However,most of the current electrocatalysts need to be applied to the working electrode with the adhesive,which increases the resistance virtually,weakens the effective specific surface area.Therefore,developing a controllable construction of self-supporting metal sulfide composites,increasing the specific surface area of the material,reducing the agglomeration effect of its own nanostructures,and exploring the mechanism of ammonia-catalyzed synergistic nitrogen fixation will have a role in promoting the development of nitrogen fixation at room temperature and piezoelectric pressure,which have important theoretical and practical significance.This dissertation focuses on the controllable preparation and electrocatalytic nitrogen fixation properties of self-supporting metal sulfide-based electrode materials.Firstly,the orderly assembly of metal sulfides on the upper surface of the conductive carrier foam nickel was achieved by a solvothermal method,and which has a larger specific surface area and more active sites.Based on this,active semiconductor nanofibers was prepared by combining with electrospinning technology,and then the semiconductor fiber-metal sulfide dual-catalyst composite was prepared using the fiber membrane as a carrier,and its electrocatalytic synergistic nitrogen fixation was explored.mechanism.The main results of this study include two aspects as the following:（1）Through self-assembly growth under solvothermal conditions,flower-like SnS₂and forest-like ZnS nanoarrays are grown on nickel foam in one step.This method can combine metal sulfides SnS2 and ZnS with conductive matrix foam Nickel is directly combined without the need for an adhesive to achieve a self-supporting electrode material.In addition,nickel foam has significantly better performance than carbon-based materials due to its good electrical conductivity and mechanical stability.The results show that SnS₂@Ni has the highest ammonia yield is 9.17×10^–10mol s^–1cm^–2and Faraday efficiency of 10.8%at–0.5 V vs.RHE;meanwhile,studies have shown that forest-like ZnS@Ni composite catalysts The highest ammonia yield at–0.5 V vs.RHE is 5.27×10^–10mol s^–1cm^–2,and the Faraday efficiency is 5.62%.（2）Combined with electrospinning technology,a supportable TiO₂fiber membrane was prepared.At the same time,CoS nanosheets were generated on the fiber surface by self-assembly via solvent heat.Finally,oxidation polymerization of dopamine in-situ and carbonization,which were used to prepare CoS nanometers.The sheet is vertically assembled on the surface of TiO₂nanofibers and the carbon nanolayer（C@CoS@TiO₂）on the outermost surface,which is a dual-active electrocatalyst.Moreover,during this process,Co-O coordination bonds are formed between the CoS nanosheets and the TiO₂fibers,a close bond is established at the interface.And the introduction of a carbon nano-plating layer increases the carrier transport performance.Experiments show that this dual-active self-supporting catalyst has a high ammonia yield is up to8.09×10^–10mol s^–1cm^–2,and Faraday efficiency of 28.6%,and good repeatability and long-term durability.