Cathode Glow Discharge Electrolysis Fabrication of Flower‐Like Ni(OH) 2 ‐Co(OH) 2 /Graphite Flake Nanocomposites for Ultrahigh Energy Density Asymmetric Supercapacitor

Transition metal hydroxides are promising electrode materials for supercapacitors due to their multiple oxidation states, high theoretical capacitance, and abundant resources. However, poor cycling stability, low energy density, and limited conductivity restrict their practical applications. Herein, a 3D Ni(OH) 2 ‐Co(OH) 2 /graphite flake nanoflower assembled from dozens of 1.7 nm ultrathin nanosheets was synthesized in a mixed solution of NaCl and Co(NO 3 ) 2 via cathode glow discharge electrolysis (CGDE), in which nickel foil served as both the anode and Ni 2+ source, while a tapered graphite rod contacting the solution interface acted as the cathode and nano‐graphite flake source. Electrochemical measurements show that the nanoflowers deliver a specific capacitance of 3777 F g −1 at 1 A g −1 and retain 84.4% of the initial capacitance after 10 000 cycles at 5 A g −1 . The assembled asymmetric supercapacitor (ASC) exhibits an energy density of 84.2 Wh kg −1 at a power density of 933.1 W kg −1 with 85.3% capacitance retention after 10 000 cycles. The outstanding performance is attributed to the synergistic effects of abundant oxygen vacancies, large specific surface area (295.7 m 2 g −1 ), and excellent conductivity. Compared with conventional synthesis routes, CGDE provides a simple, controllable, and environmentally friendly strategy for preparing advanced electrode materials.