Design Of Multiple Metal-Organic Frameworks Nanomaterials For Electrocatalysis

As the resource crisis of non-renewable energy and the tension of environmental pollution increase,the evolvement of renewable energy needs to be solved urgently.Hydrogen energy ranks among the most popular new energy materials due to its advantages for high-energy and zero-contamination.Hydrogen production by electrocatalytic water splitting has the advantages of convenient method,simple operation,high purity,etc.It is a reliable hydrogen production mode.However,due to the low utilization rate of water splitting catalyst,its promotion and application are severely restricted.Therefore,the development of efficient,stable and economical electrocatalytic materials can improve the efficiency of water splitting,promote the promotion and application of hydrogen production by electrocatalytic water splitting in the direction of new energy,advance the country’s energy transition and improve the status quo of environmental governance in my country’s high-quality development.Compared with traditional catalytic materials,metal-organic frameworks（MOFs）have adjustable functional sites,which can directionally regulate the density and position of active sites,and facilitate the optimization of catalytic performance.Therefore,this paper selects the third group transition metals Fe,Co,Ni and different organic ligands to coordinate and assemble,and successfully synthesize a variety of multi-metal MOFs materials by solvothermal method.The electrocatalytic performance differences of these multi-metal MOFs materials were explored through tests for morphology,different metal composition and ratio of multi-metal MOFs materials,as well as the effects of organic ligand functional groups and ratios on their catalytic properties were analyzed.The research methods and conclusions are as follows:（1）The four types of 2-amino-terephthalic acid,2-triazole-terephthalic acid,2-dimethylimidazole-terephthalic acid and 2-benzimidazole-terephthalic acid organic ligands with different functional groups were coordinated with Fe/Ni bimetals,and four types of MIL-53were successfully prepared.These four types of MIL-53 were respectively loaded on activated carbon cloth to form integrated electrodes with self-charged catalysts.Through analysis of morphology and crystal structure characterization,it was proved that these four different morphologies of MIL-53 had the same crystal structure.In the energy spectrum analysis,it was determined that the nitrogen atom in the triazole functional group of MIL-53（Fe Ni）-C2 could improve the electronic environment of the Fe ion active center,but could not improve the electronic surrounding of the Ni ion active center.In the electrocatalytic performance test,compared with the other three functional groups,MIL-53（Fe Ni）-C2 with a two-dimensional flake morphology had the best OER catalytic capability.At a high current density of 50 m A cm^-2,its overpotential was only 291 m V,and it also had excellent long-lasting stability.（2）The isomeric ligand 4,6-hydroxyisophthalic acid（L₂）was introduced into MOF-74 by solvothermal method,and a MOF-74 isomorph Fe Co-L₁L₂ was successfully synthesized.Through the crystal structure characterization,it was proved that Fe Co-L₁L₂ had the same crystal structure as MOF-74.In the energy spectrum analysis,it was proved that the isomer ligand L₂replaced the partial ligand L₁ to coordinate with the metal ion,which could enhance the coupling of the bimetallic Fe and Co in Fe Co-L₁L₂.Through performance testing,it was found that the catalytic performance of Fe Co-L₁L₂ with bimetal and dual ligands was better than that of single metal and single ligand samples.Moreover,when the ratio of bimetal to dual ligand approaches1:1 at the same time,Fe and Co metal ions and L₁ and L₂ ligands achieved coordination balance.At a current density of 10 m A cm^-2,the overpotential of Fe Co-L₁L₂ was only 283 m V,which was26 m V lower than commercial Ir O₂.The Tafel slope and electric double layer capacitance were31.6 m V dec^-1 and 57.5 m F cm^-2,respectively,which had reached the better performance of current MOFs catalysts.After working for 10 hours,Fe Co-L₁L₂ still retained 98.9%of the initial potential,and its crystal structure and morphology shown limited changes.（3）Inspired by the above different functional group ligands and metal ratios,3,3-azo-bis（6-hydroxy-benzoic acid）（OSA）was used to coordinate with three metal ions of Fe,Ni and Co.A type of IR-MOF was successfully prepared.Through the crystal structure characterization,it was proved that OSA was coordinated and connected with the three metal ions of Fe,Ni and Co to form a hexagonal pore structure,and this hexagonal pore structure was an isomorphic product of the increased micro-deformation of MOF-74 pore size.The conformation of the sample could be transformed by regulating the composition and ratio of Fe,Ni and Co metal ions.Fe₃Ni₇-OSA had a nano-hydrangea-like morphology structure of self-assembled two-dimensional nanosheets,which could expose more active sites.Under the same test conditions,Fe₃Ni₇-OSA had the best OER catalytic performance.