Highly Conductive Deformation-Free Reduced Graphene Oxide Fibers : Towards High-Performance Wearable Supercapacitors

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Solution-processed graphene fiber has been introduced by a wet spinning process of liquid crystal (LC) graphene oxide because of its strong hydrogen bonding and self-assembled layered structures with nematic phases. Substantially, graphene oxide (GO) solidified with layered structures in a coagulation bath. The LC-spun GO fibers generally have highly stacked and layered structures and are uneven along the fiber axis. However, due to the insulating properties of GO fiber, a reduction process should be introduced for a practical approach. Following the chemical reduction process, the LC-spun GO fiber has abundant and irregular structural deformation on the core and shell in fiber due to significant volume shrinkage. It has poor electrical conductivity, low specific surface area, and weak mechanical properties for applying high-performance supercapacitors.Herein, we introduce deformation-free graphene fiber by extruding reduced graphene oxide (rGO) and GO hybridization. This is also used in the conventional wet spinning processes. The rGO-GO hybrid dope is a possible candidate for applying porous graphene fiber with high electrical conductivity, effective surface area, and proper mechanical strength. In addition, the rGO has high electrical conductivity with low defect sites. The fabrication method is based on modified Brodie method which generates quasi-defect-free reduced graphene oxide as introduced previous work. In particular, against LC-spun GO spinning, high-quality rGO-GO dope reveals that the rGO minimizes the self-assembly of GO and adjusts the imbibition ratio simultaneously for rapid dope solvent-coagulation exchange on extruding the graphene fiber. In addition, chemically stable rGO plays a role in a frame for supporting the fiber structure after the reduction process without the deformation of core and shell structures. Despite porous rGO-GO fiber, the significantly high circularity and effective porosity could enhance electrical conductivity (~654 S/cm, after drawing) and capacitance of supercapacitors. The graphene fiber can be applicable for wearable energy storage devices with high performance.