| Complex chemical systems are particularly important in the field of electrocatalysis,because complex chemical components will change the electronic structure of electrocatalysts and adjust the coordination environment,which is conducive to improving the adsorption energy of electrocatalytic intermediates,thereby accelerating the electrocatalytic reaction.Metal-organic framework(MOF)material is a good model for constructing complex chemical systems,and a variety of metal ions and organic ligands can coexist in the same framework material.In addition,the physical and chemical treatment of MOF can induce the synthesis of crystal-solid structure transformation,and further directional construction of MOF derivative materials with more complex chemical composition and structure,and provide new opportunities for electrocatalysis and other fields.At present,the research on the multi-metallization of MOF,post-synthetic structural transformation and the regulation of electrocatalytic performance of its derived chemical complex systems is far from sufficient.In this paper,a linear trinuclear cluster-based MOF is used as a model.Based on the extensive metal compatibility of the octahedral coordination configuration of metal ions in the cluster core,Ni2+,Co2+,Fe2+,Cu2+ and Mn2+ are doped to prepare a series of single,double,three,four and five metal MOF.It was transformed into a metal oxide/alloy nanoparticle@C composite by pyrolysis,and the electrocatalytic water splitting performance of the system was studied.The details are as follows:The first chapter is the introduction part,which mainly summarizes the structural characteristics of metal-organic framework materials and their applications in the fields of electrocatalysis,gas adsorption and separation.Then,the composition and structure complexity of metal-organic framework based on reticular chemistry are introduced.The specific application of metal-organic framework derived complex chemical systems in electrocatalysis is summarized.Finally,the purpose and significance of this topic are discussed.In the second chapter,Ni3-MOF,Co3-MOF,Ni1.65Co1.35-MOF,Ni1.89Fe1.11MOF and Ni1.32Co1.26Fe0.42-MOF were synthesized by solvent method.A series of electrocatalysts were prepared by pyrolysis of MOF[M3(bpt)2(DMF)2(H2O)2](M=Fe2+,Co2+,Ni2+,H3bpt=[1,1’-biphenyl]-3,4’,5-tricarboxylic acid)in nitrogen atmosphere at 400℃,600℃ and 800℃.NiCoFeOx@C-400 prepared by pyrolysis at 400℃ is a complex chemical system in which multi-metal oxide nanoparticles are uniformly dispersed in amorphous carbon.The size of a single nanoparticle is about 5.0～12.8 nm.X-ray powder diffraction,X-ray photoelectron spectroscopy,transmission electron microscopy and synchrotron radiation X-ray scattering series of characterizations prove that it is composed of metal alloy phase and M3O4,M2O3,MO and other metal oxide phases.The multi-component synergy between these complex phases,phase interfaces,heterojunctions,and disordered carbon structures significantly improve the electrocatalytic performance of NiCoFeOx@C-400.In 1 mol/LKOH solution,NiCoFeOx@C-400 exhibits(ηj=10=253 mV)OER low overpotential and(ηj=-10=84 mV)HER low overpotential,and can achieve full water decomposition at a battery voltage of only 1.63 V.Based on the excellent electrocatalytic performance of NiCoFeOx@C-400,this chapter provides a new perspective for the design of electrocatalytic agents with high activity and stability.In the third chapter,NiCoFeMn-MOF,NiCoFeCu-MOF and NiCoFeCuMnMOF were prepared by solvothermal method.The effects of solvothermal method,reflux method and microwave-assisted method on the size and crystal shape of MOF were systematically investigated.The tetra-metal and penta-metal MOFs synthesized by solvothermal method were pyrolyzed at 400℃,500℃,800 ℃and 900℃.The compounds pyrolyzed at 900℃ showed different kinds of alloys dispersed on the highly graphitized carbon structure and a small amount of oxide nanoparticles.These multi-metal complex phases achieve efficient electrocatalytic water splitting reactions.At a current density of 10 mA cm-2,the overpotential of OER is 283 mV,the overpotential of HER is 75 mV,and the electrochemical stability can be maintained to 40 h.In addition,the preliminary study also found that NiCoFeCu-MOF can be transformed into amorphous hydroxide a-NiCoFeCu(OH)2 also showed an ultra-low OER overpotential of 260 mV and a HER overpotential of 99 mV.Polymetallic MOF and their derivatives have shown good application potential in the field of electrocatalysis.Therefore,it is of great significance to explore the multi-metallization of MOF and their derivatives for electrocatalytic water splitting. |
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