Pyrolysis Process Analysis On Salan-Ligated Manganese Cluster/Low-Dimensional Manganese Dioxide And Its Performance In Supercapacitor/Electrocatalytic Urea Oxidation

Manganese have many oxidation valence states,most of which have a special structure,which leads to different crystal forms,defects,morphology and porosity.Manganese oxides also exhibit various different electrochemical properties.But their electrochemical performance are not enough to meet the practical application,so it is very important to make a reasonable design in light of the corresponding characteristics.On the other hand,pyrolysis is one of the methods to transform the precursor into advanced nanomaterials with special structure and performance.However,the analysis of the pyrolysis process has always been a difficult problem to solve.By studying the pyrolysis mechanism,the temperature-controllable design of derivative nanomaterials with specific functions can be realized.Therefore,designing characteristic manganese oxide composite materials by studying the pyrolysis mechanism is a new challenge.In this thesis,in view of the limitations of the current design characteristics of manganese oxide and its difficulty in accurately analyzing the challenges of the pyrolysis process,the salan-ligated manganese clusters and a variety of low-dimensional manganese dioxide materials are represented.By using thermogravimetric-mass spectrometry to capture small molecules that escaped from high-temperature pyrolysis,the process of converting manganese clusters into a composite material of manganese oxides and carbon with high capacitance was explored.Moreover,the changes in pyrolysis conditions are also used to effectively control the low-dimensional manganese dioxides of different forms to obtain excellent electrocatalytic performance with different preparation methods.The main research contents are as follows:The first chapter is the preface,expounding the research background of manganese oxides and its application challenges in electrochemistry.Then the preparation methods,development and current status of manganese oxide composite materials in electrochemical applications are introduced.Finally,the use of thermogravimetric mass spectrometry for the analysis of pyrolysis process is described,and also the application of this technology in the thermal decomposition analysis on other transition metals about capacitors and electrocatalysis are explained,along with the significance of this thesis.The second chapter introduces a salan-ligated Mn₃（Mn₃（3-Me Osalophen）₂（Cl）₂）cluster.The Mn₃ cluster is a discrete neutral molecule with three Mn atoms protected by two3-Me Osalophen-ligands,and the molecular layers stacked in the C direction and the molecular layers stacked in a direction combine Mn and O to form a cube structure,which is similar to the structure of MnO,which provides conditions for the subsequent formation of high-performance manganese oxide composite materials.Then it is pyrolyzed in an inert atmosphere to directly prepare mixed-valence MnO_x embedded in the N-doped porous carbon framework.It is worth noting that MnO_x as active sites is uniformly distributed in the carbon framework,which is different from the conventional structure of MnO_x/C composites.In addition,we also use TG-MS technology to capture small organic molecules that escape from pyrolysis to accurately understand the formation process from Mn₃ clusters to MnO_x/C,and combine other characterization methods to infer the change in the ratio of Mn²⁺/Mn³⁺in the resulting material.It helps us to clarify that a reaction may occur during the pyrolysis process,and we found that the material has a higher specific surface area of 577 m²·g^-1,which answers the excellent performance of the MnO_x/C-900 sample.We further study its electrochemical performance as an electrode material for supercapacitors.As a result,MnO_x/C-900 reached943 F·g^-1 at 1 A·g^-1 and maintained a good durability of 90%under 5000 cycles.We hope that analyzing the packing pattern of molecular clusters will provide an effective method for the directional synthesis of specific functional materials and the analysis of complex structures.The third chapter introduces three kinds of manganese dioxide with different crystalline structures,two cation intercalated two-dimensional manganese dioxide and one one-dimensional manganese dioxide nanomaterials,namely bulkδ-MnO₂,colloidalδ-MnO₂and one-dimensionalα-MnO₂.Moreover,we used TG-MS technology to track the pyrolysis process in real time,and carried out accurate process analysis on the pyrolysis process of three manganese oxides.The evolution of the crystal lattice and electronic structure of cation intercalation two-dimensional MnO₂ nanomaterials has been successfully elucidated.Further successfully realized the directional synthesis of MnO_x with a controllable structure,more active sites,and significantly improved electrochemical performance.As expected,using pyrolysis technology to build the structure-activity relationship between temperature and special structure manganese oxide,manganese oxides with different unique structures are obtained.In addition,we combined with other characterizations to discuss the nanostructures of the three derivatives in detail.As expected,at a current density of 10 m A·cm^-2 in a 1 M KOH+0.33 M Urea solution,the pyrolyzed 2D MnO₂-550 nanosheets have better UOR performance,and the overpotential relative to RHE is 1.32 V.This provides a new pathway for seeking precise structures that enhance electron/ion transport behavior.