Morphology Tuning of Ni ₃ O ₆ /Co ₃ O ₄ Donut Nanostructure as High‐Performance Positive Electrode for Aqueous Hybrid Supercapacitor

Hybrid supercapacitors (HSs) have a great potential to bridge the gap between battery and supercapacitor by offering high energy density and power simultaneously. It is highly crucial to design appropriate battery‐type electrode materials for HSs to deliver both high capacity and fast charge‐discharge performance. We report the facile route and rapid preparation technique of bimetallic oxide Ni 3 O 6 /Co 3 O 4 (CNO) nanocomposite with a unique donut‐like morphology by simple one‐step wet chemical methods. Further, the donut‐like morphology was fine‐tuned by changing the urea concentration of 5 mmol (CNO‐1), 10 mmol (CNO‐2), and 20 mmol (CNO‐3) without compromising the hexagonal (Ni 3 O 6 )/cubic (Co 3 O 4 ) crystal structure of all samples. Moreover, the three‐electrode measurements exhibit specific capacitances of 219, 284, and 231 F g −1 at 0.5 A g −1 for CNO‐1, CNO‐2, and CNO‐3, respectively. Furthermore, a HS device delivers a specific capacitance of 120 F g −1 at 1 A g −1 , along with an energy density of 47 W h kg −1 and a power density of 8500 W kg −1 . It maintains 72% capacitance retention and excellent coulombic efficiency of 99% up to 5000 cycles, signifying stable long‐term performance. Hence, this work demonstrates an effective and scalable strategy for tailoring the morphology of bimetallic oxide nanocomposites for advanced aqueous HSs.