Fabrication And Electrochemical Application Of Graphene Composite Assemblies

Graphene is a two-dimensional carbon material,which is composed of monolayers of carbon atoms tightly packed into hexagnol symmetry.Because of its extraordinary mechanical,thermal and electrical properties,graphene has great promise applications in the fields of energy,electronics,environmental and biological medicine,and so on,since its first successful fabrication.The graphene itself can not only own unique properties at the nanoscale,but can also form a novel macroscopic assembly,such as graphene paper and graphene foam.Through the preparation and fabrication of nano graphene materials in macro scale,not only the unique properties of graphene can be reflected,also can endow graphene more and more excellent performance.The preparation method with simple operation,mild conditions and low cost as well as regulation of the structure and composition of graphene assembly can make up the defects of single graphene,and therefore superior performance can be achieved.In this regard,we focused our studies on the easy preparation and regulation of the structure and composition of graphene assembly,and its application in the electrochemical energy storage and sensing is also explored.The main contents of the thesis are listed as follows:We report a new type of MnO₂-graphene nanohybrid paper fabricated by one-step electrochemical reduction of graphene oxide?GO?paper and electrodeposition of MnO₂.Our straightforward one-step synthesis of MnO₂-ERGO nanohybrid paper from metal ions precursor and GO paper has been demonstrated to be a facile,green and efficient approach to fabricate graphene-based nanohybrid paper materials.Owing to the synergistic contribution from highly conductive GO paper and high loading of MnO₂ nanowires on ERGO paper,MnO₂-ERGO paper shows significantly improved electrocatalytic activity toward H2O₂ as well as excellent stability,selectivity and reproducibility.The amperometric responses are linearly proportional to H2O₂ concentration in the range 0.1-45.4 mM,with a detection limit of 10 ?M?S/N=3?and detectionsensitivity of 59.0 ?A cm^-2 mM^-1.These outstanding sensing performances enable the practical application of MnO₂-ERGO paper electrode for the real-time tracking H2O₂ secretion by live cells macrophages.We present a facile strategy to fabricate N,S-codoped graphene paper?N,S-rGOP?by microbial method to further regulate the micro structure and component of graphene paper.Our strategy eliminates drastic conditions,cumbersome reaction procedures,and the use of toxic reagent,which allows us to prepare hybrid graphene paper under green and mild conditions and offers greater possibilities for mass production.In addition,the macro flexibilies and micro stack structure are completed retained.Owing to synergistic effect from dual-element doping,the obtained N,S-rGOP possesses high electrochemical sensing activity toward H2O₂ detection in terms of excellent sensitivity,stability and reproducibility.The amperometric responses are linearly proportional to H2O₂ concentration in the range 0.5?45.5 mM,with a detection limit of 50 ?M?S/N=3?and detectionsensitivity of 47.0 ?A cm^-2 mM^-1.Based on its good biocompatibility and cell adhesion,cancer cells can be directly growth on the surface of N,S-rGOP,which enable it for real-time tracking the secretion of a new type of cancer biomarker H2O₂ in live breast cancer cells MCF-7 in a normal state and after the radiotherapy treatment.The macro structure regulation of graphene assembly is developed as the main line,GO foam with porous structure and large surface area was firstly fabricated by solution-casting of graphene oxide?GO?nano sheets on Ni foam,then Ni,Co2x?OH?6x/graphene foam was fabricated by simultaneous electrochemical reduction of GO foam and electrodeposition of NixCo2x?OH?6x nanoflakes on it.Owing to the unique nano/micro hierarchical design combining the high electrochemical activity of NixCo2x?OH?6x/rGOF nanocomposite,high conductivity of graphene layers and large-area porous structure of 3D rGOF scaffold,when used as binder-free electrode for supercapacitor,the 3D NixCo2x?OH?6x/rGOF exhibits a high specific capacitance of 703.6 mF cm^-2 at a current density of 10 mA cm^-2 and a good rate capability of 83.8%at 10 mA cm^-2,and the specific capacitance retention remains 97.5%after 1000 cycles.Furthermore,for electrochemical biosensor application,the NixCo2x?OH?6x/graphene nanohybrid electrode exhibits high selectivity,reproducibility and stability towards the nonenzymatic detection of hydrogen peroxide.The amperometric responses are linearly proportional to H2O₂ concentration in the range 0.1?37.4 mM,with a detection limit of 10 ?M?S/N=3?and detectionsensitivity of 23.66 ?A cm^-2 mM^-1.The macro structure and micro component regulation of graphene foam is developed as the main line,we first synthesized flexible rGOF using simple compression method,and then polypyrrole nanowire/graphene foam?PPy NWs/rGOF?serves as negative material was prepared by the electrodeposition of polypyrrole nanowires on rGOF.polypyrrole@MnO₂ core-shell nanowires/graphene foam?polypyrrole@MnO₂ NWs/rGOF?served as positive material was obtained by directly growing MnO₂ film on PPy NWs/rGOF via one-step redox reaction at room temperature.One-step chemical synthesis of positive material from negative material has demonstrated to be novel and facile approach for high-performance supercapacitor fabrication.Owing to rational design of different components in negative and positive electrodes,the assembled asymmetric supercapacitor can be reversibly charged/discharged at a high voltage of 1.6 V,and displays remarkable energy density of 1.04 mWh cm-3,and the initial specific capacitance still retains 86.5%after 5000 cycles.