Investigation Of Graphene Nanoribbon Composite In Electrochemical Energy Storage And Conversion

Graphene nanoribbons?GNRs?,as a new type of carbon nano-material,have higher electronic conductivity and thermal conductivity than traditional carbon material.At the same time,due to their special open edges and ordered layered structure,graphene nanoribbons have drawn more and more attention among researchers.In this thesis,we focus on the study of the transitional metal?Fe,Co,Ni?oxide/graphene nanoribbons composites,optimization and design of the structure were carried out.The electrochemical behaviors and mechanism of these composites in the fields of lithium ion batteries,supercapacitors and electrocatalysis were also discussed.A three-dimensional composite of graphene nanoribbons crosslinked by Fe₃O₄nanoparticles,which is denoted as 3D Fe₃O₄@GNRs,is synthesized in a simple reflux way.In this hybrid,GNRs with open and active edges are used as building blocks while Fe₃O₄ nanoparticles are employed not only as anode materials but as a cross-link agent to weld GNRs at the joins,resulting in the assemble of a 3D porous composite.The 3D Fe₃O₄@GNRs hybrid have exhibited a super high cycling performance(1700 mAh g^-1over 100 cycles at 0.1 A g^-1)and an excellent rate capability(1265 mAh g^-1 at 1 A g^-1).On above basis,a series of new 3D Fe₃O₄/MO@GNRs?M=Co,Ni?composite materials were obtained by magnetic cross-linking of Fe₃O₄/MO nanoparticles.It was clarified that the formation foundation of 3D GNRs porous structure lay in the preferential aggregation of Fe₃O₄/MO magnetic nanoparticles at the junction of GNRs,which played the role of connecting and fixing graphene nanobarbels,thus constructing the 3D porous structure based on GNRs.As cathode material of lithium battery,3D Fe₃O₄/MO@GNRs composites have delivered high capacity and cyclic stability for Li⁺storage(The discharge capacities of 3D Fe₃O₄/CoO@GNRs and 3D Fe₃O₄/NiO@GNRs electrodes were 1432 mAh g^-1and 1058 mAh g^-1,respectively,over 80 cycles at 0.1 A g^-1).In addition,the superparamagnetism of two hybrids indicates that they can be suitable for potential applications in magnetic controlling devices,magnetic resonance imaging and biological separation.Based on the 3D Fe₃O₄/CoO@GNRs composite,we have mixed 3D Fe₃O₄/CoO@GNRs and graphene quantum dots?GQDs?through simple ultrasonic treatment to obtain 3D GQDs-Fe₃O₄/CoO@GNRs composite.The synergistic effect between them have improved the ORR activity of 3D GQDs-Fe₃O₄/CoO@GNRs.The hollow NiCoO₂ nanocage wrapped by interlaced graphene nanoribbons?GNRs?through electrostatic action,was denoted as NiCoO₂/GNRs.NiCoO₂/GNRs showed high electrochemical performance of oxygen evolution reaction?OER?,which exhibited small onset potential of 1.50 V and achieved current densities of 10 mA cm^-2 at potentials of 1.62 V.And the hybrid delivered high capacitance of 937.8 F g^-1 at 1 A g^-1in supercapacitors.The results showed that the electrostatic action of GNRs have improved the electrical conductivity and stability of the composite and provided more electrochemical active sites for OER at the same time.