Research On The Performance And Mechanism Of Electrocatalytic Oxidation Of 5-Hydroxymethyl Furfural By Nickel Nitride

As the chemical energy stored in organisms,biomass energy is currently the renewable carbon-containing energy that is expected to replace fossil energy,possessing great potential in solving energy crises,developing green economy,and protecting the ecological environment.5-Hydroxymethylfurfural（HMF）is one of the biomass platform compounds,which can generate a series of high-value chemical products and biofuels through redox reaction,called"Sleeping Giant".2,5-Furandicarboxylic acid（FDCA）is one of the high value-added oxidation products of HMF and can be used to synthesize green degradable plastics in industry.Compared with traditional catalytic methods,electrochemical catalysis is a kind of green and high-efficiency conversion method.Mild reaction conditions,controllable reaction rate,no additional redox reagents and simple operation platform make electrochemical catalysis attract wide attention and have been widely used in the reaction of HMF oxidation to FDCA.As the core of the HMF electrochemical oxidation reaction（HMFOR）,Ni-based catalysts show great potential and are one of the most excellent materials for efficient HMFOR.The study on the HMFOR reaction mechanism and the structure-activity relationship of Ni based catalyst have important significance.In this thesis,the nickel nitride（Ni₃N）is used as typical catalyst to systematically study its performance,reaction path and oxidation mechanism of HMFOR.The main contents are as follows:（1）Using glucose as the carbon source,carbon-coated nickel nitride nanosheets（Ni₃N@C）were grown in situ on a nickel foam substrate.The coated carbon layer can not only effectively maintain the nanosheet structure of Ni₃N,and increase its stability and active sites,but also regulate the electronic structure of Ni₃N and improve its intrinsic catalytic activity.When Ni₃N@C is used in HMF electrocatalytic oxidation reaction,the Faraday efficiency is as high as 99%,and the yield of FDCA is also stable at about 98%.After 6 consecutive cycles of electrolysis,it still has good catalytic activity.At the same time,Ni₃N@C has good hydrogen evolution performance.In a two-electrode system composed of hydrogen evolution reaction（HER）and HMF oxidation reaction,driving a current density of 10 m A cm^-2 only requires a cell pressure of 1.46 V,indicating that Ni₃N@C can effectively realize the simultaneous production of hydrogen energy and high value-added compounds.Aiming at the problem of unclear oxidation path of HMF,this work uses in-situ and frequency resonance spectroscopy（SFG）for the first time to explore the path of HMF electrocatalytic oxidation,demonstrating that HMFCA is the main reaction path under this reaction condition.（2）Through various in-situ and quasi-in-situ analysis methods（XANES,Raman,EIS,and XPS）,the active species and reaction mechanism of Ni₃N-catalyzed HMF oxidation were explored;that is,Ni²⁺on the catalyst surface is oxidized to Ni³⁺under the action of electricity,and OH in water is adsorbed.The active species Ni³⁺N（OH）_ads is formed later;the active species reacts spontaneously with the HMF molecules and then returns to the Ni²⁺state,and the HMF molecules are oxidized.The catalyst material continuously undergoes dynamic evolution between Ni²⁺and Ni³⁺throughout the process.In addition,by analyzing and comparing the reaction rate of HMF and the distribution characteristics of reaction products under different alkali concentrations,it is found that a high OH^-concentration environment is conducive to the formation of Ni³⁺,and it is also conducive to the adsorption of HMF molecules on the electrode surface,thereby increasing the overall oxidation reaction rate.This study deepens the understanding of the electrocatalytic reaction of HMF by explaining the oxidation mechanism and the influence of alkali concentration.