Rational electrode architectural design, favorable electrode composition, and versatile synthesis approach play a significant role in developing advanced electrodes for high-performance supercapacitor. In this work, we report a facile approach for fabricating 1D hierarchical CuO@Co x Ni 1−x (OH)2 nanowire arrays grown on 3D highly conductive copper foam. The optimized CuO@Co0.2Ni0.8(OH)2 electrode delivers an ultrahigh specific capacity of 374.7 mAh g−1 at 2 A g−1 with exceptional rate capability (301.7 mAh g−1 at 50 A g−1) and remarkable cycling stability (95.9% after 10 000 cycles at 50 A g−1). A flexible asymmetric solid-state supercapacitor (ASC) is fabricated using the optimized CuO@Co0.2Ni0.8(OH)2 as the positive electrode, activated carbon-coated nickel foam as the negative electrode, and polyvinyl alcohol/KOH gel as electrolyte. The flexible ASC operating with a potential window of 0–1.6 V delivers an energy density of 46.5 Wh kg−1 with a power density of 526.9 W kg−1. The ASC also exhibits excellent cycling stability with a capacity retention of 84.3% after 10 000 cycles at a current density of 7 A g−1.