Facilely Hierarchical Growth of N‑Doped Carbon-Coated NiCo₂O₄ Nanowire Arrays on Ni Foam for Advanced Supercapacitor Electrodes

Ternary NiCo₂O₄ has attracted tremendous interest as a type of prospective electrochemical energy storage material. Hence, a facile and economical preparation method for N-doped carbon-coated NiCo₂O₄ (NiCo₂O₄@NC) nanowire array electrodes is reported by simply dipping the NiCo₂O₄ nanowire arrays grown on Ni foam substrate into a dopamine aqueous solution followed by annealing in an argon atmosphere. The hybrid NiCo₂O₄@NC nanowire arrays grown on a Ni foam substrate is directly employed as a 3D-structure porous electrode without adhesive. Compared with the original NiCo₂O₄ nanowire array electrode, the hierarchical hybrid NiCo₂O₄@NC nanowire array electrode delivers a higher capacitance, better rate performance, and excellent stability (final capacity remains 91.3% at 10 A g^–1 after 5000 test cycles). An asymmetric supercapacitor based on NiCo₂O₄@NC//active carbon is designed and achieves a high energy density of 29.4 Wh kg^–1 at a power density of 349 W kg^–1 with superior capacitance retention of 97.3% at 5 A g^–1 after 15,000 cycles. The improvement of the electrochemical energy storage property demonstrates the potential of the hierarchical NiCo₂O₄@NC nanowire array electrode in the electrochemical energy field.