The development of low-cost and earth-abundant electrocatalysts with efficient energy conversion and excellent super-capacitive storage is highly desirable for practical applications. Herein, three-dimensional sea urchin-like Co(OH)₂@CuO structure nanocomposites were successfully synthesized by an ammonia coordination strategy. Compared with Co(OH)₂ and CuO electrocatalysts, the optimized Co(OH)₂@CuO composite exhibits excellent oxygen evolution reaction activity and supercapacitor performance due to the synergistic effect between them. The as-prepared Co(OH)₂@CuO-2 electrocatalyst displays a low overpotential of 361 mV to drive 10 mA cm^–2 and a long-term durability during at least 30 h of OER testing. In addition, Co(OH)₂@CuO-2 also exhibits a high capacitance of 270.8 F g⁻¹ at 0.5 A g⁻¹ when used as a supercapacitor electrode. This work provides a new idea for developing highly active, low-cost bifunctional electrocatalysts for electrochemical conversion and energy storage.