Thermal Decomposition And Electrical Behavior Regulation Of Brucite-like Zn/Co-based Coordination Molecular Clusters Based On O-vanillin Schiff Base

Nanostructured materials such as porous carbon,porous metal oxides and its composites have been widely studied for storage tools and energy conversion,catalysis and gas storage.In recent years,in order to obtain materials with high electrochemical performance,suitable precursors and synthesis methods are particularly important,among which heterogeneous synthesis methods provide many unique properties.Common anion doping,namely nitrogen doping into carbon materials,can not only improve the wettability of electrolyte solution,the accessibility of active surface area and the combination with ions,but also improve the conductivity by enriching the density of free charge carriers.Although ion doping has not been systematically studied,cation doping or heterogeneous metal doping has flourished in the energy field.However,the distribution of metal atoms in doped metal molecular clusters has been a crucial problem restricting the pyrolysis preparation process for many years.How to use coordination chemistry and anion substitution methods to construct new reaction systems and guide the synthesis of derivative materials of coordination molecular clusters is a very challenging topic.In this thesis,two molecular clusters with zinc participation coordination were synthesized based on o-vanillin Schiff base ligands,and the electrical behavior of their pyrolysis products was regulated by low temperature pyrolysis and high temperature pyrolysis.Zn/Co-doped coordination molecular clusters based on brucite-like discs were successfully prepared.The thermal decomposition process was analyzed by the organic small molecular fragments captured by TG-MS,and the stability of the solid-liquid structure of the compounds was investigated by PXRD and ESI-MS.At the same time,XRD,TEM,IR,Raman and XPS were used to study the changes of material composition,crystallization degree and element valence state of the products under low temperature and high temperature pyrolysis.At the same time,the effects of structural evolution of molecular clusters after low temperature and high temperature pyrolysis on OER catalytic activity and capacitance performance were explored.The thesis is divided into three chapters:The first chapter is a preface that outlines the research background and scientific challenges of doped complex derived materials and their energy conversion and energy storage.Then,the development history and current situation of doped coordination molecular cluster derived materials for supercapacitors and electrocatalytic oxygen evolution are introduced.Finally,the TG-MS tracking precursor decomposition process and the progress and advantages of designing and regulating doped coordination molecular cluster derived materials are analyzed.Combining the good foundation of our research group for the design,assembly process and mechanism research and electrical behavior of seven-core disc-like molecular clusters,the significance of the topic selection is introduced.The second chapter introduces the synthesis of a brucite-like disc-like compound[Zn₇L₆（OCH₃）₆][ZnLCl₂]₂ by selecting N/O-dichelated 2-methoxy-6-methylmethyleneaminophenol ligand（HL）,and then introducing cobalt atoms by anion substitution to obtain a Zn-Co doped compound[Zn₇L₆（OCH₃）₆][Co₂Cl₅]（compound 1）.In this work,the catalyst and porous carbon materials were prepared by pyrolysis of compound 1 from room temperature to 900℃ in a helium atmosphere.Thermogravimetric analyzer（TG-MS）was used to explore the fracture of organic small molecule fragments of molecular clusters under low temperature pyrolysis and high temperature pyrolysis and analyze the gas information escaped during pyrolysis.The solid-liquid structure correlation,structural characteristics and the thermal decomposition process of Zn₇Co₁ were studied by combining various techniques and characterization methods.The solid-liquid structure stability of Zn₇Co₁ was investigated by PXRD and ESI-MS.SEM/TEM,XPS and BET were used to characterize and analyze the related phases.When the pyrolysis temperature reaches 900℃,the porous carbon structure containing micropores is left on the surface due to the escape of liquid zinc near its boiling point（907℃）,which is a potential supercapacitor material.Through the introduction of the above mechanism,at 700℃,the proportion of Zn and Co elements is just the best ratio,Co atoms are drilled into the micropores left by the escape of liquid Zn,and a porous carbon structure is obtained.The surface area is 274 m²·g^-1,the pore volume vluea of about 0.253cm³·g^-1,and the capacitance is 1389 F·g^-1 at a current density of 1 A·g^-1.The doped clusters with unique structure were obtained by post-synthesis modification of anion substitution,and the electrical behavior was controlled by pyrolysis temperature.In the third chapter,a compound 2 based on L3 ligand was introduced.The ligand（H2vanen）was obtained by aldehyde amine condensation reaction of ethylenediamine and o-vanillin.The ligand and metal Zn were solvothermally reacted at a certain temperature to synthesize[Zn₄（H2vanen）₃（Cl）₂]（compound 2）.In this work,we synthesized tetranuclear Zn-based molecular cluster Zn4,and combined with PXRD,SEM/TEM,XPS and other characterization methods to study their structural characteristics.At 900℃,liquid Zn leaves vacancies due to evaporation to obtain a microporous porous carbon structure,it provides perfect conditions for the subsequent formation of high-performance supercapacitor materials.A series of N-containing porous carbon materials were obtained by temperature gradient pyrolysis.At the same time,we combined TG and TG-MS to explore the internal mechanism of the pyrolysis process of precursor molecular clusters,and analyzed the process of Zn4molecular clusters forming porous carbon structure,which helps us to explore the whole process of pyrolysis.As a result,2-900 reached 1785 F·g^-1 at 1 A·g^-1,maintaining a good durability of 90%under 5000 cycles.We hope to lay a foundation for exploring potential high-performance electrochemical materials by directional design of molecular clusters.