Functional Assembly Of Graphene Toward Stimuli-response And Energy-related Applications

Graphene,a unique two-dimensional single-carbon-atom layer conjugate structure,has excellent physical and chemical related properties,which presents considerable potential in a variety of research areas,combining with designed moifications.In this thesis,various graphene based stimuli-responsive materials have been prepared through controllable electrochemicalmethods,includingelectro-responsivegraphenecomposite,multi-responsive graphene composite and moisture-responsive graphene oxide.Additionally,their applications in information storage,sensing and energy conversion have been investigated.1)Electro-responsive graphene compositeThe graphene is modified by graphitic carbon nitride to fabricate composite film.Wherein,the coupling effect of graphene and graphitic carbon nitride is consisted by electrostatic interactions andπ-πstacking,which can be tuned by applied voltage,dominating the charge transfer between them.As a result,the composite is enabled with electro-responsive bistable conductivity,achieving an all-carbon based flexible information storage with high ON/OFF ratio of 10~4.2)Multi-responsive graphene compositeThe graphene is modified by graphitic carbon nitride oxide by selective electrochemical deposition.The obtained composite,which has rugged morphology and tunable oxygen content,presents different conductivity upon variation of external force,humidity and temperature,i.e.stimuli-responsive multi-stable conductivity.Remarkably,according to the result from 1),the feedback signals of specific stimulus can be enlarged,achieving selectivelu senstive detection of external stimuli.3)Moisture-responsive graphene oxideA novel moisture assisted electrochemical polarization has been developed to accurately regulate the distribution of oxygen containing groups in graphene oxide assemblies,realizing the gradient of ionizable functional groups(e.g.carboxyls).The obtained material has beem used to demostrate a newly developed mositure-enabled power generation as follow:a.An efficient moist-electric energy transformation has been discovered by means of establishing the oxygen-functional-group gradient in the graphene oxide films.Combining the moisture-responsive property and electrical un-stability of graphene oxide(GO),a moisture-sensitive graphene oxide films with gradient oxygen-containing groups is prepared by the moisture assisted electrochemical polarization,which can accordingly induce rapid and repeatable charging of the film upon exposure to the moisture.The moisture variation(30%)served as an energy source to generate electric power with voltage output of up to ca.30 mV.Based on this finding,a prototype power generator and self-powered respiratory monitor have been demonstrated under the stimuli of the human breath.b.A high performance chemical potential energy harvester has been successfully fabricated for directly generating electric power based on a superhydrophilic and porous three-dimensional assembly of graphene oxide with preformed oxygen-containing group gradient.The open framework of this specially designed graphene oxide assembly largely facilitated the diffusion of water molecules to produce the dissociated charged ions as free-carriers.Meanwhile,its asymmetrical oxygen-containing groups enabled a voltage output of ca.1.5 V under a humidity variation of 75%.Its potential as a practical power source was evidenced by lighting the LED.c.A porous membrane of self-assembled graphene oxide nanoribbon networks that enabled with a potential switching by external stimulus of moisture.The resulting membrane can provide significant moisture triggered voltage output of 40 mV upon humidity variation of 30%within c.a.80μs.This unique property allows the fabrication of novel self-powered data recording device with high ON/OFF ratio of 10~6.