Freestanding vanadium nitride nanowire/nitrogen-doped graphene paper with hierarchical pore structure for asymmetric supercapacitor anode

Abstract

Vanadium nitride (VN) is a promising anode material for asymmetric supercapacitors (ASCs) owing to its high theoretical pseudocapacitance and high electrical conductivity. However, the instability of VN in aqueous electrolytes hinders practical applications. In this study, VN nanowires (VNNWs) were hybridized with nitrogen-doped graphene (NG) to fabricate a freestanding VNNW/NG porous paper electrode. The prepared paper electrode exhibited excellent electrochemical performance with an outstanding specific capacitance of 244.7 F·g−1 at 0.5 A·g−1 and a rate capability of 70.7% capacitance retention as the current density increased from 1 to 10 A·g−1. Moreover, the VNNW/NG anode presented remarkable cycling stability of 87% capacitance retention over 10,000 cycles at 5 A·g−1. Encapsulation with NG significantly improved the stability of VNNWs, overcoming their major drawbacks (i.e., low cycling stability). Also, the hierarchical pore structure of the VNNG/NG could facilitate high energy and power density capabilities. An ASC assembled with VNNW/NG anode and nickel oxide/reduced graphene oxide (NiO/rGO) cathode presented high energy density of 20.2 Wh·kg−1 at power density of 850.0 W·kg−1. Thus, we suggest that the design strategy of the fabricated porous paper electrode could be utilized to produce high-performance anode materials for application in supercapacitors.