Sandwich-Structured Transition Metal Oxide/Graphene/Carbon Nanotube Composite Yarn Electrodes for Flexible Two-Ply Yarn Supercapacitors

Carbon nanotube (CNT) yarn has been regarded as a perfect electrode material for linear flexible supercapacitors. However, the supercapacitors composed of pure CNT yarn electrodes always have lower specific capacitance and energy density. In this work, a pseudocapacitive material composed of a transition metal oxide mixture (Co3O4@NiO) is electrodeposited on the CNT yarn surface and followed by coating of a layer of graphene (GN) to improve the electrochemical performances of the as-fabricated flexible supercapacitor. The deposited NiO Co3O4 and the coated GN on the CNT yarn surface form a uniform hybridized CNT/Co3O4@NiO/GN layer like a sandwich. The two-ply yarn supercapacitor based on the sandwich-structured CNT/Co3O4@NiO/GN composite yarn displays excellent electrochemical properties with a volumetric capacitance of 263.34 F/cm(3) at 0.01 V/s. The two-ply yarn supercapacitor also shows a high energy density of 5.86 mWh/cm(3) and a power density of 263.64 mW/cm(3). In addition, the high electrochemical performance of the two-ply CNT/Co3O4@NiO/GN yarn supercapacitor is flexible and can be knitted into fabrics for wearable electronic devices.