Distinctive Supercapacitive Properties of Copper and Copper Oxide Nanocrystals Sharing a Similar Colloidal Synthetic Route

CuO and Cu₂O are non-noble transition metal oxide supercapacitive materials with high theoretical specific capacitances above 1800 F g⁻¹. In this work, by adjusting organic additives of a colloidal system, Cu, Cu₂O, and CuO are grown in situ on nickel foam. CuO exhibits a specific capacitance of 1355 F g⁻¹ at 2 A g⁻¹ in 3 m KOH, a value well above those of Cu and Cu₂O (<500 F g⁻¹), and is superior to other known CuO electrodes. The CuO electrode exhibits 70% of its initial capacity, and the Columbic efficiency remains ≈100% after 7000 cycles at 4 A g⁻¹. Cu₂O exhibits the worst electrochemical performance, mainly due to the inactive barrier layer forming on the surface. This work provides an efficient synthetic platform for both comparable supercapacitive studies and cost-effective electrochemical energy storage applications.