Construction of an Ni3V2O8/CoMoO4 core–shell heterostructure with urea as an additive and its capacitive properties in high-performance asymmetric supercapacitors

Abstract

In this work, a core–shell heterostructure cathode (Ni₃V₂O₈@CoMoO₄-A) consisting of a Ni₃V₂O₈ nanowire core and a vertically coated CoMoO₄ nanosheet shell is controllably synthesized by a two-step hydrothermal method using urea as a morphology regulator. Urea slowly releases OH⁻ ions via a homogeneous precipitation mechanism, which effectively promotes the heterogeneous nucleation and dense growth of CoMoO₄ on the Ni₃V₂O₈ surface. The material presents a well-developed porous structure and abundant redox-active sites. Three-electrode tests show that the electrode exhibits a specific capacitance of 952.1 F g⁻¹ at 1 A g⁻¹ with a retention of 94% after 10 000 cycles. A CNT/Fe₂O₃ composite anode is prepared by loading α-Fe₂O₃ nanoparticles onto acidified carbon nanotubes, integrating high conductivity and high pseudocapacitive activity. An asymmetric supercapacitor is assembled with Ni₃V₂O₈@CoMoO₄-A as the cathode and CNT/Fe₂O₃ as the anode, which operates stably at a voltage of 1.4 V. The asymmetric supercapacitor assembled with these positive and negative electrodes operates stably within a 1.4 V voltage window. When the power density is 750 W kg⁻¹, the energy density reaches 215 Wh kg⁻¹; after 10 000 cycles, the capacitance retention remains 95.9%. This work demonstrates that the combination of interface engineering and structural regulation can significantly improve the performance of supercapacitors, providing a feasible strategy for developing high-performance aqueous energy-storage devices.