The Synthesis And Electrochemical Performance Of Co-MOF-74-based Catalysts For Oxygen Evolution Reaction

High-efficient electrocatalysts for oxygen evolution reaction?OER?play a crucial role in the energy storage and conversion.A lot of research has shown that metal-organic framework materials?MOFs?have gradually become a research hotspot in OER due to the ultra-high specific surface area,regular pore texture and isolated active sites.In this thesis,a series of Co-MOF-74-based catalysts with good electrocatalytic performance are designed and prepared based on the structural advantages and application foundations of MOFs.The main contents of this thesis are as follows:1.The synthesis and electrochemical performance of Co_xFe_1-x-MOF-74?0<x?1?catalysts for oxygen evolution reaction.A series of bimetallic Co_xFe_1-x-MOF-74?0<x?1?catalysts were synthesized by a facile hydrothermal method with Co²⁺and Fe²⁺as metal sources and 2,5-dihydroxy terephthalic acid as organic ligand.The study found that the morphology and electronic structure of Co-MOF-74 can be effectively regulated by the different contents of Co and Fe,which can provide more metal active sites and facilitate effectively synergistic reaction between Co and Fe.The ionization potential of Co-MOF-74 also changed to significantly enhance the catalytic performance.Among all MOFs samples,Co_0.6Fe_0.4-MOF-74 exhibited the best electrochemical oxygen evolution reaction property,with a Tafel slope of 56 mV/dec,an overpotential of 280mV to generate a current density of 10 mA/cm² in 1 mol·L^-1 KOH solution and a good stability.A water splitting cell employing Co_0.6Fe_0.4-MOF-74 and commercial Pt/C as anode and cathode respectively,exhibited a current density of 20 mA/cm² at 1.58V,presenting a promising application.2.The synthesis and electrochemical performance of CoFe-MOF-74/TCNQ catalysts for oxygen evolution reaction.The 7,7,8,8-Tetracyanoquinodimethane?TCNQ?modified CoFe-MOF-74composite catalyst was successfully synthesized by adding a certain amount?-conjugated molecules during the synthesis of CoFe-MOF-74 using one-step hydrothermal method.The experimental results found that the TCNQ guest molecules was modified into the one-dimensional channels of CoFe-MOF-74.The structure of CoFe-MOF-74 was not affected by TCNQ molecules,and the conductivity is enhanced for an improved catalytic activity of OER.The analysis of XRD,FT-IR and XAFS demonstrated that the structure of CoFe-MOF-74/TCNQ and CoFe-MOF-74will be reconstructed during OER.The rate of structural reconstruction,the structure and activity of reconstructed products are greatly influenced by the TCNQ.Because of the strong electronic interaction between CoFe-MOF-74 and TCNQ,the reconstruction process of CoFe-MOF-74/TCNQ is relatively slower than that of CoFe-MOF-74.At the same time,TCNQ acts as a support in the one-dimensional channel of CoFe-MOF-74,ensuring that the structure of catalyst is not easy to collapse during oxygen evolution.And the active sites of the catalyst are also maintained,resulting in a steady catalytic reaction process.3.The synthesis and electrochemical performance of Co-MOF-74/MPc catalysts for oxygen evolution reaction.The Co-MOF-74/CuPc,Co-MOF-74/ZnPc and Co-MOF-74/CoPc composite catalyst were successfully synthesized by adding?-conjugated metal phthalocyanine?CuPc,ZnPc,CoPc?during the synthesis of Co-MOF-74 using one-step hydrothermal method.The study found that the crystal structure of Co-MOF-74 is not affected by MPc molecules,and the electrochemical oxygen evolution activity of the composite catalyst is improved.Because of the strong electronic interaction between Co-MOF-74 and CuPc,Co-MOF-74/CuPc exhibited the best electrochemical oxygen evolution reaction properties.Further research found that Co-MOF-74/CuPc had the largest electrochemical active area,smaller charge transfer resistance and a good stability,compared with Co-MOF-74 and CuPc.It mainly attributed to the?-conjugated system of CuPc molecules can induce the electron interaction between Co-MOF-74 and CuPc,which can improve the charge transfer ability and produce more unsaturated active sites.The structure of Co-MOF-74 and Co-MOF-74/TCNQ were both reconstructed after the electrochemical stability test.Co-MOF-74transformed into Co₃O₄,while Co-MOF-74/CuPc transformed into Co₃O₄/Cu₂O hybrid.