Graphene-based Functional Assemblies And Their Applications In Energy Related Fields

Graphene is a two-dimensional planar structured carbon material with a single layer of atomic thickness.Its unique physical and chemical properties promote it to apply in many fields.Reasonable structural assembly of graphene is an important way to realize its practical applications.Based on new methods and new effects,this thesis breaks through the structural limitations of traditional graphene assemblies,and designs as well as realizes novel graphene-based functional assemblies from micro/nano-scale to macro-scale at different scales.The electrochemical energy conversion and storage properties of graphene-based assemblies at various scales were studied.The main achievements of the dissertation were as follows:1.Zero-dimensional graphene-based nanocapsules?1?We have developed a substrate-induced method to prepare nitrogen-doped porous graphene nanocapsules.Theoretical calculations confirmed that the substrate has an enhancement effect on the nitrogen doping of graphene and pore-forming process.Benefiting from a high nitrogen doping content,large specific surface area and hierarchically porous structure,these nanocapsules exhibit excellent bifunctional electrocatalytic activity and stability toward oxygen reduction-oxygen evolution reaction,even close to commercial Pt/C and RuO₂ electrocatalysts.?2?Using the novel"dopamine-like"molecule as a carbon precursor,the controllable preparation of the defect-rich porous graphene-like nanocapsules was realized by the template method.These nanocapsules possess an ultrahigh specific surface area,a hierarchically micro/mesoporous structure and a high pyridine N-doping content.Electrochemical tests show that the graphene-like nanocapsules exhibit excellent bifunctional electrocatalytic activity and stability toward hydrogen evolution-oxygen evolution reaction,which is superior to all other reported metal-free water splitting electrocatalysts.2.One-dimensional graphene composite fiberWe have designed and prepared two novel graphene composite fibers with a core-shell structure,i.e.manganese dioxide/reduced graphene oxide/carbon fiber with hierarchical structure and three-dimensional porous graphene hydrogel wrapped copper wire,which exhibit excellent energy storage performance.Furthermore,a fiber based flexible all-solid-state asymmetric supercapacitor is successfully assemblied by using these two fibers.Owing to the synergistic effect of different components in the composite fiber,the device displays a wide working potential window,high area/volume energy density,excellent flexibility,good rate capability,and long-term cyclability.3.Two-dimensional graphene nanomesh filmFor the first time,we have realized the controllable fabrication of large-area ultrathin graphene nanomesh film by in-situ carbothermal reduction of spontaneously assembled graphene hybrid film.The abundant nanopores in graphene nanomesh provide a high density of cross-plane ion diffusion channels.As a result,the graphene nanomesh film-based supercapacitors exhibit high volumetric capacitance,ultrahigh power density,ultrafast frequency response,excellent mechanical flexibility,and long-term cyclability.Thus,it is promising to replace commercialized aluminum electrolytic capacitors for AC line-filtering in future flexible electronics.4.Three-dimensional graphene composite bulk?1?Based on the multiple synergistic effect,we have developed a simple and inexpensive method to achieve large-scale preparation of three-dimensional graphene/Pd composite foam.The obtained composite foam as a self-supported electrode exhibits superior ethanol electro-oxidation activity and stability,much higher than commercial Pd/C catalysts.?2?Guided by the design of high performance lithium-ion battery electrodes,a new type of three-dimensional graphene nanomesh coupled hollow transition metal oxide composite aerogel was successfully prepared.Due to the structural advantages of graphene nanomesh and hollow metal oxide,which can synergistically provide a robust structure and efficient electron/ion transport pathways,the resultant composite aerogel as a negative electrode material exhibits ultrahigh specific capacity,excellent rate capability,and cycling stability.