Nest-like V3O7 self-assembled by porous nanowires as an anode supercapacitor material and its performance optimization through bonding with N-doped carbon

Abstract

Vanadium oxides (such as V₂O₅, V₂O₃ and VO₂) hold great promise as electrode materials for energy storage due to their high electrochemical activity, low cost and environmental benignity. However, V₃O₇ is rarely investigated as a supercapacitor material. Herein, nest-like V₃O₇ self-assembled by porous V₃O₇ nanowires was fabricated. The energy storage mechanism of V₃O₇ was investigated at different reaction potentials. It was found that V₃O₇ was converted to V₆O₁₃ at a potential of −0.6 V, and became V₂O₅ at 0.2 V. Additionally, an in situ photopolymerization method was introduced to synthesize V₃O₇@polypyrrole (PPy) and then, V₃O₇ nanowires coated with a layer of N-doped carbon were obtained after calcination to enhance the performance in terms of capacitance and stability. This unique N-doped carbon coated nest-like V₃O₇ (NC-V₃O₇) exhibited a high specific capacitance of 660.63 F g⁻¹ at a current density of 0.5 A g⁻¹ and even reached 187.72 F g⁻¹ at a high current density of 50 A g⁻¹. According to this investigation, the superior performance of NC-V₃O₇ is attributed to the synergy between N-doped carbon and V₃O₇, that is, the unique three layer structure (C bonded both to V and N) stabilized V₃O₇ and supported high-speed ionic and electronic transmission channels. Finally, full symmetric (NC-V₃O₇//NC-V₃O₇) and asymmetric (MnO₂ nanosheets//NV-V₃O₇) supercapacitor devices were assembled and showed higher power and energy density than those of related reports.