Synthesis Of MOF-based Nanomaterials And Study Of Their Electrocatalytic Properties

Metal-Organic Frameworks?MOF?is a coordination polymer with a three-dimensional structure.In general,metal ions?M?are used as the connection points,and organic ligands?O?form a spatial 3D extension.The assembly of the periodically arranged skeleton structure?F?for modification or host-guest assembly to form a crystalline porous material with a network structure is a novel porous material except zeolite and carbon nanotubes.MOF has many advantages,such as the material has a large specific surface area,developed void structure,adjustable pore size,open metal sites,easy functionalization of the pore surface,and diverse composition.It has potential applications in the fields of gas adsorption,storage and separation,energy storage and conversion,fluorescence,chemical sensing,drug release,and catalysis,and MOF has become an important research frontier.On the other hand,materials scientists also use MOF as a method of metal precursor dispersion,which is converted into a corresponding carbon-based material by direct high-temperature pyrolysis of MOF materials,and MOF is used in functionalized carbon materials,or the synthesis of single atoms.The microscopic morphology and state of the catalyst are closely related to the preparation methods.The morphology of the catalysts obtained by different preparation methods is quite different,and the catalyst activity tends to be very different.MOF is modified by non-precious metals such as transition metal manganese?Mn?and molybdenum?Mo?.Metal salts such as Mn and Mo and ligands containing N in MOF formed bimetallic MOF materials with different morphologies.Composites constructed by this method have excellent ORR,OER,HER properties,good conductivity and high capacitive storage capacity.These composites not only retain the structure of MOF precursors,but also have high specific surface area and uniformly dispersed active sites.In this paper,MOF materials?compounds formed by organic ligands containing elements such as nitrogen/oxygen and metal ions through self-assembly process?ZIF-67?transition metal cobalt as central ion and 2-methylimidazole as organic ligand?are precursors.A series of nanocatalyst composites were synthesized by modifying the ZIF-67 with transition metals Mn and Mo.These materials not only retain the structure of the ZIF-67 precursor,but also have a high specific surface area and a uniformly dispersed active site.Those materials can be used as good electrochemical nanocatalysts.The specific research contents of this paper mainly have the following aspects:Firstly,A manganese seed-mediated coordination growth method was used,and the cobalt ion in cobalt hexahydrate was used as the central ion,and 2-methylimidazole was used as the organic ligand to synthesize the ZIF-67 dodecahedral basic this structure.The manganese-cobalt oxide catalyst was confirmed by SEM,TEM and STEM.It can be seen that the catalyst has layered pores and rhombohedral dodecahedron nanocage structure with side length of about 200 nm and manganese cobalt oxide nanocrystal size of 2-50 nm.The mapping image confirmed that Mn,Co,and O were uniformly distributed in the catalyst.XPS demonstrated that the surface of MnCo₂O_4.5 nanoparticles contains Co²⁺,Co³⁺,Mn²⁺and Mn³⁺,which can provide good electrochemical catalytic activity for ORR and OER.The hollow MnCo₂O_4.5 nanocage catalyst was used as the air electrode for constant current charge and discharge test.The results show that the catalyst has good stability.Secondly,using Mn-ZIF-67 as a template and cetyltrimethylammonium bromide?CTAB?as a surfactant,using a stirring method to obtain a core-shell structure Mo/Mn-ZIF-67 nanomaterial catalyst The side length is about 500 nm and the surface of the material is pleated.The core of the Mo/Mn-ZIF-67core-shell structure increases with the stirring time,and the core becomes smaller and smaller.When the stirring time is longer than 120min,a single-layer shell structure is formed.The catalyst consists of Co,Mo,Mn,C,and O.Co is mainly distributed in the core,and Mo is distributed in the outer shell.Mo/Mn-ZIF-67core-shell structured catalysts have good electrochemical catalytic activity and stability for ORR,OER and HER,and Mo/Mn-ZIF-67 can be used for water splitting catalysts.Thirdly,Using ZIF-67 as template material,sodium molybdate dihydrate?Na₂MoO₄·2H₂O?as the molybdenum source and CTAB as the surfactant,the bimetallic CoMoO₄ nanocatalyst with core-shell structure was obtained by calcining at 900°C in a nitrogen atmosphere.Both the inner core and the outer shell maintain the dodecahedron structure of ZIF-67.The side length is around 500 nm,the outer shell has pleats and the inner core has evenly distributed nanoparticles.The main constituent elements of the catalyst are Co,Mo,C,O,Mo is distributed in the outer shell,and Co is mainly distributed in the inner core.The bimetallic CoMoO₄ compound with special morphology has better electrochemical activity of ORR,OER and HER,and can be used as a three-function catalyst.In this paper,ZIF-67 is used as a precursor to provide non-precious metal cobalt and rhombohedral dodecahedral metal organic framework.By simple synthesis method,different transition metals such as manganese?Mn?and molybdenum?Mo?are introduced to design and synthesize the morphology.The MOF-based metal oxides with uniform morphology and stable structure were synthesized.These catalysts have good electrochemical catalytic activity or stability and can be used in ORR,OER,and HER,providing an experimental basis for the commercialization of zinc-air battery catalysts.