Study On Construction Of Nickel-based MOF Catalyst And Its Urea Electro-oxidation Performance

The development of renewable energy sources and wastewater treatment for the environment have become currently the major focus of global attention.Urea electrooxidation reaction（UOR）has received extensive attention due to its effective reduction of hydrogen production energy consumption and purification of urea-rich wastewater.The development of UOR electrocatalysts with high catalytic activity and excellent stability has emerged as a research hotspot in the current field.Based on the fact that UOR is still at the stage of mechanistic investigation,this paper takes nickel-based MOFs catalysts as the object of study and uses the characteristics of MOFs materials that can regulate metal active sites and organic ligands,such as t-NFPBA@LDH and Ni Rh Mn MOF catalysts were constructed to investigate the active sites of UOR.The effect of interfacial synergistic effect on the stability and electrocatalytic performance of UOR in t-NFPBA@LDH catalyst and the synergistic effect of Ni Mn bimetallic and functional carboxylic acid ligands（CLs）on the electrocatalytic performance of UOR in Ni Rh Mn MOF catalyst were investigated by material characterization,electrochemical testing,and in situ Raman.Meanwhile,this thesis realizes the identification of active sites and the regulation of local electronic states in the UOR process,reveals the important factors and their interactions in the UOR reaction mechanism,and provides theoretical guidance for the development of efficient and stable UOR electrocatalysts,which contributes to the sustainable development of UOR applications.The main research results are as follows.（1）Using"Interface engineering"to induce interfacial bonding to accelerate local electron transfer,reveals the microscopic mechanisms of interfacial construction on the regulation of intrinsic catalytic activity,UOR stability augmentation and active sites of materials.In this paper,three-dimensional nanoflower structures（t-NFPBA@LDH）were grown on nickel foam substrates by a one-step hydrothermal method based on the physical properties of nickel-iron Prussian blue pyrolysis at high temperature and pressure,and applied to OER and UOR in alkaline solutions.Through in-situ surface-enhanced Raman（SERS）and in-situ impedance（SEIS）analysis at different voltages,show that the active site of t-NFPBA@LDH during UOR is electrophilic lattice oxygenα-Ni（OH）O,and the active site of NFPBA is electrophilic adsorption oxygenγ-Ni OOH.The excellent stability of UOR can be attributed to the local electron redistribution caused by the in-situ special interface（M₁-O-N≡C-M₂）,in which electrons are transferred from Ni and Fe atoms to adjacent bonded N atoms through O atoms,and the lattice oxygen ligand environment of Ni（II）-O in MOFs/LDH is adjusted to optimize the generation potential of electrophilic lattice oxygenα-Ni（OH）O.The urea-degradation rates of t-NFPBA@LDH,t-NFLDH and NFPBA were～92.72%,～78.03%and～68.56%,respectively.The urea fuel cell had a maximum power density of 1.87 m W/cm² at 7.01 m A/cm²,which was substantially greater than that of commercial Pt/C（0.75 m W/cm² at 3.97 m A/cm²）.（2）The asymmetric coordination trimetallic MOFs structure was constructed by“Metal node engineering”,revealing that the double-site（Ni and Mn）catalysis and synergistic CLs can accelerate the transfer of OH^-during the UOR process,thereby reducing the reaction barrier of UOR.Mn-Ni Rh MOF nanosheets were grown in situ array on nickel foam substrate by one-step solvothermal method,and the electronic structure analysis confirmed that the introduction of Mn induced the local electronic state changes of Ni and Rh,making it bifunctional（HER//UOR）.The electronic state and in-situ Raman show that the O^2-terminal electron cloud is induced by the shift to Mn,which reduces the coordination ability of Ni-O,allowing the isolation of organic ligands and thus faster delivery of OH^-,and improves the catalytic activity of UOR by optimizing the generation potential of the active species Ni Mn（OH）x.Through the urea degradation test,the degradation rates of Ni MOF,Ni Rh MOF and Ni Rh Mn MOF were～77.4%,～83.5%and～99.7%,respectively.At the same time,the power densities of zinc-air batteries with or without urea were 67 m W/cm²and 70 m W/cm²,respectively,and the current densities were 124 m A/cm² and 136 m A/cm²,respectively.The energy conversion efficiency（53.3%）was higher than that of conventional zinc-air batteries（47.3%）.