Fabrication and characterization of highly porous cobalt oxide coated graphene fibers for supercapacitors

Abstract

Graphene fibers have attracted attention as new carbonaceous fibers to substitute for carbon fibers due to their properties such as light, high mechanical and electrical properties. As a raw materials, graphene oxide was produced by Hummers method. Unlike conventional graphene synthesis methods such as arc discharge, laser ablation, and CVD, Hummers method is useful to produce graphene oxide from graphite due to possibility of mass production and inexpensiveness. Fabricated graphene oxide solution represented liquid crystalline properties. Owing to this liquid crystalline properties of GO, graphene fibers by wet spinning had aligned graphene sheet structure in a uniaxial direction. Due to it, graphene fibers had high performance properties by interaction between graphenes. However, it is not suitable for supercapacitors because their structure induced low surface area. Therefore, in this study, electroplating was applied to fabricate vertically porous $Co_3 O_4$ at surface of graphene fibers for enhanced porous structure and supercapacitive properties. Here, graphene fibers was produced by wet spinning. And fabricated graphene fibers was electroplated to form $Co_3 O_4$ at surface of fibers Mechanical properties of graphene fibers were analyzed by micro tensile tester and X-ray to evaluate alignment. Electrochemical properties were analyzed by three electrode cell (6M KOH) such as CV curve, galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS). Fabricated $Co_3O_4$/Graphene fibers exhibited highest specific capacitance due to porous structure at surface and synergistic effect of EDLC and psudocapacitor. Based on this study of fabricating $Co_3 O_4$/Graphene fibers by electroplating, applying this process to graphene fibers by continuous process is expected to further improve properties.