Hierarchical NiCoP nanosheet arrays with enhanced electrochemical properties for high-performance wearable hybrid capacitors

Transition metal phosphides (TMPs) are battery-typed materials with superior conductivity and redox activity, thereby making them promising in fiber-shaped hybrid capacitors (FSHCs). Yet designed synthesis of nanostructured TMPs on conductive fiber substrate as binder-free electrode is essential to improve their electrochemical performance. This work proposes an efficient strategy to directly grow hierarchical NiCoP nanosheet arrays (NSAs) on carbon nanotube fibers (CNTFs) by using a hydrothermal process and subsequent gas-solid phosphorization. Benefiting from the ordered nanosheet structure, the NiCoP/CNTF electrode exhibits a specific capacity of 0.711 mAh cm(-2) at a current density of 1 mA cm(-2). Matching this electrode with a negative electrode of CNTF supported vanadium nitride (VN) NSAs, we fabricated a high-performance twisted FSHC with a maximum operating voltage of 1.6 V. Owing to the ultrahigh electrochemical performance of the hybrid fiber electrodes, the FSHC device delivers a high specific capacitance of 325.6 mF cm(-2)(108.53 F cm(-3)) at the current density of 1 mA cm(-2), and achieves an energy density of 115.78 mu Wh cm(-2). Moreover, it displays excellent flexibility with negligible capacitance loss after 5000 bending cycles. Thus, this work elucidates a feasible route to construct NiCoP-based fiber electrodes for wearable energy storage devices. (C) 2018 Elsevier B.V. All rights reserved.