Studies On The Controlled Synthesis And Performance Of Graphdiyne-based Multiscale Electrocatalysts

Graphdiyne is a new type of carbon allotrope with China’s independent intellectual property rights.It is an all-carbon material with a two-dimensional planar network structure formed by a carbon-carbon alkyne bond(sp-C)conjugated to a benzene ring(sp2-C).In 2010,the research group of Pro.Li in the Institute of Chemistry,Chinese Academy of Sciences,successfully synthesized graphdiyne for the first time around the world,which opened up a new field of carbon materials.The unique chemical and electronic structure of graphdiyne endows it with many unique and novel properties,such as rich carbon chemical bonds,rich natural pore structure,super conjugated system,intrinsic band gap,high conductivity and excellent chemical and mechanical stability.In particular,the extremely uneven distribution of the surface charge of graphdiyne makes it has very high surface activity,bringing high intrinsic activity,and easily producing peculiar physical and chemical properties.In addition,graphdiyne is the only carbon material that can achieve controllable growth on any substrate surface under mild condition,showing unique advantages in the growth and assembly of highly active interface structures.Graphdiyne has almost all the structures and properties of ideal advanced materials and is a material that can bring innovative development.Since the first successful synthesis in 2010,the study of graphdiyne has received extensive attention from scholars in different fields around the world,and has rapidly developed into a new research field and hotspot."Graphdiyne Research" was selected as the Top 10 frontier hotspot in the field of chemistry and materials science in the report "Research Fronts 2020" released by Institutes of Science and Development,Chinese Academy of Science,National Science Library.Chinese Academy of Science and Clarivate.According to the statistics of the National Science and Technology Library,there are more than 60 countries and regions including the United States,the United Kingdom,the European Union and Japan and more than 500 research teams from the Institute of Chemistry of the Chinese Academy of Sciences,Peking University,Tsinghua University and other wellknown university research institutes in the world to carry out graphdiyne research,which has greatly promoted the rapid development of graphdiyne research in the world.Graphdiyne has shown revolutionary performance in basic and applied research in the fields of catalysis,energy,photoelectric conversion,life science,intelligent information and devices.In this thesis,based on the unique structure and properties of graphdiyne,a series of multiscale graphdiyne-based catalysts were controllably prepared for the key problems of low catalyst activity,poor selectivity and poor stability in hydrogen energy and carbon dioxide conversion systems,and successfully applied to electrocatalytic nitrate to ammonia,olefin epoxidation,CO2 fixation to esters and other catalytic reactions.We also systematically studied the catalytic reaction mechanism in the reaction process and clarified the structure-activity relationship between the active site structure and catalytic performance,which revealed the key role of the unique structural properties of graphdiyne in improving the selectivity,activity and stability of the reaction and the new properties,new phenomena and new effects brought by graphdiyne.This thesis includes the following parts:(1)In the Chapter 1,based on the basic structure of graphdiyne,we introduced various special physical and chemical properties of graphdiyne,and summarized the commonly used preparation strategies of graphdiyne.The research and application of graphdiyne in catalytic science are mainly introduced.The current research results of graphdiyne in energy conversion and storage,intelligent photoelectric information science,life science and material separation science are also introduced in detail.(2)In Chapter 2,the successful anchoring of zero-valent copper atoms on the surface of graphdiyne is realized by making full use of the space confinement of the hole with rich alkyne structure and the incomplete charge transfer property between alkyne bond and metal atoms.In the prepared catalyst,zero-valent copper atoms exhibit a highly uniform dispersion.The incomplete charge transfer behavior between graphdiyne and copper atom not only stabilizes the copper atom but also promotes the transfer of electrons during the catalytic reaction,providing abundant active sites,resulting in excellent reaction selectivity,high ammonia yield and high long-term stability in electrocatalytic ammonia synthesis.(3)In Chapter 3,aiming at the problem of low Faraday efficiency in the process of electrocatalytic epoxidation of olefins at room temperature and pressure,zero-valent iridium atom was uniformly anchored on the surface of graphdiyne by electrochemical reduction method,named iridium atom catalyst.The epoxidation of styrene was carried out by the active oxygen substance produced by electrolysis of water.The incomplete electron transfer between graphdiyne and zero-valent iridium atoms improves the charge transfer ability between the catalyst and the substrate,forming a large number of active sites and improving the catalytic efficiency.The Faraday efficiency of epoxidation reaches more than 45%,realizing the complete green catalytic process of epoxidation of olefins at room temperature and pressure.Theoretical calculations show that the iridium atom catalyst exhibits a reaction process which different from the traditional pathway,which promotes the in-depth exploration of the olefin epoxidation process.(4)In view of the scientific problem of efficient CO2 fixation reaction under environmental conditions,zero-valent cobalt atom which exhibits excellent CO2 adsorption activity was anchored on the surface of graphdiyne by electrochemical method in the form of single atom to achieve efficient CO2 conversion.We finally obtained nearly 100%conversion and selectivity,and achieved high yield and conversion frequency.The incomplete electron transfer between graphdiyne and cobalt atom effectively promotes the electron transfer from cobalt atom to graphdiyne,accelerating the electron transfer between the intermediate and the catalyst in the catalytic process,and finally realizes the efficient catalytic conversion of CO2.(5)By taking full advantage of the unique physical and chemical properties of the graphdiyne,we finely regulated the structure of platinum-manganese alloy quantum dots anchored on the surface of graphdiyne,and obtained a graphdiyne-based zero-valent bimetallic alloy quantum dot catalyst.The zero-valent platinum-manganese alloy quantum dot catalyst is easier to obtain oxygen atoms from water molecules to electrocatalytically oxidize styrene to phenyl glycol.In the process of regulating the structure of alloy quantum dots,it is found that the proportion of platinum in the alloy has an influence on the valence state of platinum and manganese.Reducing the content of platinum in the quantum dot will lead to the increase of the valence state of manganese firstly,and then leading to the increase of the valence state of platinum.The change of catalyst structure in the reaction process has also been accurately characterized.Through the construction of graphdiyne based catalytic system,the precise regulation of catalyst structure can be realized and the change of active sites in the reaction process may be explored,also the structure-performance relationship and catalytic reaction mechanism can be deeply understood.(6)Reasonable group substitution of the precursor of graphdiyne may obtain structure tunable carbon-based functional materials.Methyl and hydrogen-substituted graphdiyne derivative nanowires can be prepared by replacing the three alkyne bonds in the hexaynebenzene with methyl groups(MGDY)and hydrogen atoms(HGDY),respectively.This strategy can precisely regulate the chemical and electronic structure of the active site,obtain high-performance catalytic materials,and understand the reaction process and mechanism on the catalytic site at the atomic scale.Theoretical research and experimental results show that the delocalized electron density of carbon atoms in the alkyne bond is higher in MGDY due to the electron-donating effect of methyl.The faster charge transfer ability on the active site resulting in better catalytic performance and higher catalytic stability.(7)In Chapter 7,we summarized and gave a future prospect of the thesis.