Design And Preparation Of Metal Coordinated Polymer Derived Electrocatalysts And Study On Electrocatalytic Reduction Nitrate Properties

Ammonia（NH₃）is a key chemical in agriculture,industry,and national defense.At present,the large-scale synthesis of NH₃ mainly relies on the traditional Haber-Bosch method,which has problems such as large carbon dioxide emissions and excessive energy consumption.Therefore,the development of green and low-energy preparation methods is of great significance to achieve large-scale ammonia production.The electrocatalytic nitrate production technology for ammonia has advantages such as the use of renewable electricity and the use of water as a proton source,and is considered an alternative to the traditional Haber Bosch method.Electrocatalytic reduction of nitrate to ammonia involves a multi electron/proton transfer process,which involves the generation of by-products and low ammonia selectivity.Therefore,how to design high-efficiency and low-energy electrocatalysts has become the focus of current attention.Metal catalysts with highly occupied d-orbital and unclosed d-orbital shells have been widely studied in the field of electrocatalytic nitrate reduction,and the advantages of d-orbital electrons to promote the lowest empty orbital charge injection of nitrate are used to promote the reaction.At present,metal based catalysts have the problem of having few active centers.One of the effective ways to solve this problem is to build metal coordination polymer electrocatalysts to increase the active centers.However,metal-coordinated polymers have poor stability in non-neutral electrolytes,which is not conducive to practical applications.In this paper,the electrocatalyst of metal coordination polymer derivative was constructed by hydrolysis reaction and pyrolysis,which exposed more active sites,promoted the transport of electrons and intermediates,and improved the electrocatalytic reduction of nitrate.The specific research content of this paper is as follows:（1）Cobalt-based coordination polymers are grown in situ as Co（OH）₂ nanosheets for electrocatalytic nitrate reductionCobalt-based coordination polymer（Co-CP）was prepared from squaric acid and cobalt acetate tetrahydrate.Co-CP grows two-dimensional Co（OH）₂ nanosheets（Co-CP-OH）in situ in KOH solution at p H13.The NH₃ yield rate of Co-CP-OH catalyst is 6.2 mg h^-1 mg_cat.^-1at-0.7 V vs.RHE,the Faraday efficiency（FE）reaches 92.6%and has good electrochemical stability.By comparing the structure of Co-CP in different p H KOH solutions and its electrocatalytic nitrate reduction performance,the high ammonia yield benefits from the formation of Co（OH）₂ nanosheets,exposing more active site,and promoting the contact between reactants and active site.（2）Synthesis of three-dimensional iron based coordination polymer Fe@C Application in electrocatalytic nitrate reductionIron-based coordination polymer（Fe-CP）was prepared from squaric acid and ferrous acetate tetrahydrate,and then Fe-CP was used as a precursor and pyrolyzed into iron nanoparticles（Fe NP）in an argon atmosphere at high temperature into nanohybrid material（Fe@C）encapsulated in the carbon layer.Fe@C has good electrocatalytic activity and structural stability in electrocatalytic reduction of nitrate to ammonia.At-0.6 V vs.RHE,the NH₃ yield rate reaches 5.1 mg h^-1 mg_cat.^-1,FE up to 94%.Fe@C prepared with Fe-CP as a precursor can expose more active sites and promote the electron interaction and electrocatalytic reaction between Fe NP and the carbon layer.