Research On Electrocatalytic Nitrate Reduction Reaction Based On Interfacial Microstructures Regulation Strategy

Nitrate anion（NO₃^-）is one of the most widespread pollutants in water resources,which seriously threatens human health and ecological environment.Electrochemical conversion of NO₃^-to high value-added chemicals driven by renewable electric energy is a crucial approach to achieve nitrate pollutant degradation and energy conversion.Electrocatalytic NO₃^-reduction and coupling with carbon dioxide（CO₂）molecules at ambitious temperature and pressure are expected to replace the traditional energy-intensive Haber-Bosch and Bosch-Meise technology to realize highly selective generation of ammonia（NH₃）and urea.Nevertheless,complex multi-electron proton transfer process and competitive proton reduction reaction greatly restrict the catalytic activity and selectivity of nitrate reduction reaction（NO₃RR）.As a consequence,it is of great significantly to design highly efficient and selective nitrate reduction systems.In this dissertation,several highly selective nitrate reduction electrocatalytic nanostructures were designed by optimizing the electronic structure and coordination environment of the catalysts and regulating the microenvironment of mass transfer and intermediates adsorption at the interface.（1）Interface defect engineering via signal-atom doing was demonstrated to effective electrocatalytic NO₃RR to NH₃.The isolated Fe atoms could induce the formation of abundant oxygen vacancies defect and occurrence of charge redistribution at the atomic interface of TiO₂ and Fe atoms.The electron-deficient Fe sites could facilitate the adsorption and activation of NO₃^-and suppressing the competitive proton reduction.Fe signal atom modified TiO₂（Fe-TiO₂）electrocatalyst shows excellent NO₃RR performance with NH₃ generation yield rate 137.3 mg h^-1 mg_cat^-1 and Faradaic efficiency of 92.3%at-1.4 V（vs.RHE）.This work provides novel insights for the exploration of highly efficient nitrate reduction electrocatalysts via heteroatom doping and interface defect engineering.（2）Zr-based metal organic framework was used as functional skeleton to load Cu Zn bimetal nanocluster and smart channels were in situ constructed for highly selective electrocatalytic nitrate reduction to NH₃.The electron interaction between Cu Zn bimetal nanoclusters could promote the adsorption and activation of NO₃RR intermediates.The pendant Br（?）nsted acidic groups（COOH）of MOF not only could stabilize the key*HNO intermediate and optimize the*H intermediate adsorption barrier to inhibit the competitive proton reduction reaction.The as-proposed interfiacl microstructure strategy provides a novel route for the application of functional MOF in nitrate reduction reaction and is expected to be applied to other electrocatalytic systems.（3）Polycation-functionalized catalysts electrode was established to optimize C-N coupling interface microenviroment,promoting electrocatalytic co-reduction of CO₂ and NO₃^-to urea.The poly-N-（6-aminohexyl）acrylamide（PNHA）polymer abundant polyamine nodes is conducive to in situ capturing of CO₂ molecules,filtering of proton and stabilizing*CO intermediates.Ni Fe bimetallic nanocluster（Ni Fe NC）could promote the adsorption and activation of CO₂ and NO₃^-reactants and C-N coupling intermediates.PNHA polymer modified Ni Fe NC（Ni Fe NC-PNHA）electrode shows outstanding electrochemical C-N coupling and urea generation activity,which delivers urea generation yield rate of 1254.2μg h^-1 mg_cat^-1 and Faradaic efficiency of 83.4%.This work provides new insights in optimizing reaction kinetics and intermediates adsorption via microenvironments regulation to selective electrochemical C-N coupling and urea production.（4）The orderly coating of bilayer polymer configuration with CO₂ molecules capture and permeation behavior was designed for boosting electrocatalytic C-N coupling reaction and urea generation.Polymer of intrinsic microporosity（PIM）with hydrophobic rigid structure is selected to restrict the proximity of protons,inhibit the competitive proton reduction and promote the mass transfer and penetration of CO₂ molecules.Polyaniline（PANI）with abundant basic amino groups is enables to trigger chemical interaction with acidic CO₂ molecules,which could capture and induce the accumulation of CO₂ and reactant around electrode surface,thus facilitating the carbon source supply for C-N coupling.Ni Fe dual atoms electrocatalyst（Ni Fe DAC）acts as an available site for adsorbing and coordinating reactants and key C-N coupling intermediates.PANI and PIM polymers modified Ni Fe DAC electrodes（Ni Fe DAC-PANI-PIM）shows impressing C-N coupling performance,which delivers maximum urea generation yield rate of 1671.6μg h^-1 mg_cat^-1 and Faradaic efficiency of 75.3%.In addition,the N and C atoms selectivity of Ni Fe DAC-PANI-PIM electrode for electrochemical synthesis of urea are as high as93.9%and nearly 100%,respectively.The microenvironment kinetics modification strategy provides novel insights for the exploration of highly efficient and selective C-N coupling and other gas-involved reactions catalysts.