| Reasonable design and synthesis of efficient electrocatalysts for oxygen evolution reaction（OER）is key to energy conversion.From the perspective of coordination chemistry,there are generally two strategies to improve the intrinsic electrocatalytic performance of metal-organic drameworks（MOFs）:（1）regulating the interaction between metal centers through metal ion doping;（2）changing the electronic structure of the active metal center through ligand modification.In this thesis,a series of isomorphic mono-and bi-metallic MOFs based on Co（II）and Ni（II）were synthesized by using squaric acid as organic ligand.The OER electrocatalytic activity of MOFs was regulated by change the doping ratio of metal elements.The electrocatalytic study showed that the OER electrocatalytic activity of MOFs was the best when the doping ratio of Co/Ni was1:1.Two cobalt-based MOFs were synthesized from tetrazole ligands with different side groups,5-nitroisophthalic acid and Co（II）salt.The OER catalytic activity of MOFs can be controlled by changing the side group of tetrazole ligand.When the side group of the tetrazole ligand changes from–NH2 to–CH3which has a stronger electron-donating ability,the electrical conductivity（EC）of the corresponding MOF increased by two orders of magnitude,and the OER overpotential decreases from 385 m V cm-2 to 318 m V cm-2 at 10 m A cm-2.The full text is divided into three chapters:In the first chapter,the significance of OER electrocatalysts for the energy conversion and utilization of renewable energy,the characteristics of transition metal-based OER electrocatalysts,and the advantages and disadvantages of homogeneous and heterogeneous OER catalysts were introduced.Then the advantages of MOFs as OER electrocatalysts and the mechanism of OER in different media were described.Finally,the common strategies for regulating the OER activity of metal-organic framework electrocatalysts were presented.In the second chapter,[Co3-xNix（C4O4）2（OH）2]·n H2O with different Co/Ni doping ratios,named as MOF-1,MOF-2,MOF-3,MOF-4,MOF-5,MOF-6 and MOF-7,were obtained through the hydrothermal synthesis of squaric acid and transition metal salts.PXRD characterization confirmed that they were isomorphic,and ICP-MS revealed that the proportion of Co/Ni in the synthesized bimetallic MOFs is almost the same as the feed ratio.When immersed in0.1 M H2SO4,1 M H2SO4and 1 M KOH solution,the stability of the framework can still be maintained,which showed that the synthesized MOFs have excellent acid and alkali stability.The above MOFs were loaded on hydrophilic carbon paper for OER performance test.The results showed that MOF-5 had the most excellent electrocatalytic OER activity.When the current density was 10 m A cm-2,the overpotential of MOF-5 was 290 m V,and the corresponding Tafel slope was 75 m V dec-1,which was much smaller than other bimetallic or monometallic MOFs and superior to commercial Ru O2 electrocatalyst.At the same time,MOF-5 also showed excellent catalytic stability with a minimal increase in overpotential after 75 h of electrolysis.In the third chapter,two cobalt-based MOFs,that is[Co2（μ3-O）（Hnip）（mtt）（H2O）]·1.5H2O（named as Co-CH3）and[Co2（μ3-O）（Hnip）（att）（H2O）]·1.5H2O（named as Co-NH2）,were synthesized by fine-tuning the side groups of tetrazole ligands.Thermogravimetric analysis and PXRD spectra verified that Co-CH3 and Co-NH2 had excellent thermal and alkaline stability.When Co-CH3 and Co-NH2 were immersed in 0.1 M PBS solution for 48 h,the nanosheets with unchanged framework structures were obtained,named as Co-CH3-NS and Co-NH2-NS,respectively.Transmission electron microscopy（TEM）showed that Co-CH3-NS and Co-NH2-NS are ultra-thin nanosheets with graphene-fold-like shapes.Atomic force microscopy（AFM）height images showed that the thickness of Co-CH3-NS and Co-NH2-NS is about 6 nm.The OER performance test was carried out on the glassy carbon electrode,and the results showed that the catalytic performance of the metal-organic nanosheet electrocatalysts was adjusted in a controlled manner by replacing–NH2 group with–CH3group,and the corresponding OER overpotential reduced from 385 m V cm-2to 318 m V cm-2 at 10 m A cm-2.The catalytic performance was superior to the commercial precious metal-based catalyst Ru O2.At the same time,Co-CH3-NS exhibited higher catalytic stability and its overpotential nearly does not increased after electrolysis for 10 h.The PXRD spectra for the catalyst before and after electrolysis were completely consistent.In addition,the electrical conductivity test for the nanosheets showed that the conductivity of Co-CH3-NS and Co-NH2-NS was 6.96×10-7 S cm-1 and 1.55×10-9 S cm-1,respectively.Obviously,when the side group of the tetrazole ligand was changed from–NH2 to–CH3,the corresponding EC of the nanosheets increased by two orders of magnitude.Moreover,combined with the calculation of Electron Localization Function（ELF）by Density functional theory（DFT）,it is confirmed that the types of ligand side groups can indirectly adjust the electronic structure of catalytic metal center and the degree of electron localization of metal-organic nanosheet catalyst,thus accurately regulating the OER catalytic performance of the catalyst. |
