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

CuO and Cu 2 O 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, Cu 2 O, 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 Cu 2 O (<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 . Cu 2 O 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.