The Structure Regulation, Functional Assembly And Application Study Of Graphenes

Graphene, a two-dimensional monolayer sheet of sp2-bonded carbon atoms, hasattracted increasing attention in recent years due to its extraordinary electrical, mechanical,thermal properties, large specific surface area, and relatively low manufacturing cost. Inthis thesis, based on the graphene material, we foucs on the desination and development ofthe new structure and assembly of the graphene to explore the novle sturcture and uniqueproperties, which will further expand the application of graphene in energy strorage andconversion. Herein, the regulation and assembly for graphene are carried out by two ways:the structure regulation and the functional assembly of graphene. Based on above results,the graphene based functional materials have been applied into the energy strorage andconversion fields.1．Structure regulation of grapheneA simple and efficient method for regulating the intrinsic structure of graphenequantum dots has been established. N-doped graphene quantum dots (N-GQDs) with theN/C atomic ratio of ca.4.3%were prepared by electrochemical strategy, which showunique optoelectronic features distinctive from those of their N-free counterparts. Themethod has been efficient regulated the inherent optical and electronic properties ofgraphene quantum dots which providing a new application for graphene quantum dots inenergy conversion.2．Functional assembly of graphene1) Assembly of macroscopic one-dimensional structure of grapheneA continuous coaxial wet spinning technique has been developed, relazing thecontinuously engineered production of morphology-defined, graphene oxide hollowmicrofibers (GO-HFs) on a large scale with a high throughput. One meter of GO-HFs isgenerated within30s with a production rate of3.3cm s-1. GO-HFs has beenwell-controlled produced with ease of functionalization and can converse to G-HFs viathermal or chemical reduction. Besides, a necklace-like structure of the GO-HFs can beperpared by controlling the compressed air within the internal capillary of the coaxial device.2) The three-dimensional assembly of grapheneA new method for the assembly of ultralight graphene materials with small moleculehas been demonstrated. Due to the molecular interaction between pyrrole molecule andgraphene, a versatile, ultralight, three dimensional (3D) graphene frameworks was preparedby one-step hydrothermal treatment, which mainly consists of the network of only fewgraphene layers, and has an ultra-low density of2.1±0.3mg cm-3. It exhibits a highadsorption capacity, thermal stability and excellent elctrochenmical properties.Based on the above method, On the one hand, the approach for metal oxide assisted insitu etching holes within three-dimensional graphene has been developed. The graphenenanomesh foam with pore-hierarchical arrangement has been successfully fabricated with asite-localized iron oxide nanoparticle-induced etching process. Besides, the N (S) doped orco-doped graphene nanomeshes have also been achieved. On the other hand, the method forin-situ electrochemical synthesis of graphene functional composites has been demonstrated.The3D polypyrrole-graphene (PPy-G) foam was formed by direct electro-polymerizingPy-containing3D graphene. The as-formed PPy-G foam is durably tolerant to the largecompressive strain without any structural collapse and loss of springiness.In addition, with the2D graphene sheets as the template, the in-situ formed1Dgraphitic carbon nitride (g-C3N4) nanoribbons assembled on graphene sheets has beenachieved by using a simple one-step hydrothermal method, which leads to the rationallyassembled3D architecture of1D g-C3N4nanoribbons with2D graphene sheets, and theformation of g-C3N4nanoribbons on graphene sheets can be controllable by tuning thereaction parameters.2．Applications of graphene and graphene-based functional materialsThe graphene and graphene-based functional materials which were fabricated throughregulating and assembling process have been applied in the related electrochemical energyconversion and storage fields.In the electrochemical energy conversion: Both the N-GQDs electrode supported bygraphene sheets and the nitrogen and sulfer co-doped graphene nanomesh electrode havebeen demonstrated to possess the high electrocatalytic activity showing excellent oxygen reduction performance. G-HFs produced with ease of functionalization can be assembledinto an optoelectronic device exhibiting high photoelectronic properties. In addition, theprepared3D architecture of in-situ formed1D graphitic carbon nitride (g-C3N4)nanoribbons with2D graphene sheets exhibit highly efficient electrocatalytic ability in thehydrogen evolution reaction with low overpotential, small Tafel slope and extremely largeexchange current density.In the electrochemical energy storage: The assembled ultralight3D grapheneframeworks supercapacitor shows a high specific capacitance of484Fg-1which isapproaching to the theoretical capacitance of pure graphene and can also be used as a newmetal-free catalyst for efficient electrocatalytic oxygen reduction reaction. Due to the highcompression and electrochemical performance, the PPy-G foam can be used as thedeformable electrodes for assembly of highly compression-tolerant supercapacitors withhigh specific capacitances.