In situ facile surface oxidation method prepared ball of yarn-like copper oxide hierarchical microstructures on copper foam for high performance supercapacitor

• The ball of yarn-like CuO hierarchical microstructures were prepared by a simple surface oxidation method.
• The as-prepared samples can be used as binder-free electrodes without further treatment.
• The CuO/copper foam electrodes exhibit excellent long life stability (98.11% retention after 20000 cycles).
• Prepared ball of yarn-like morphology and 3D Cu foam both provide countless active sites.
• The maximum specific capacitance of 762.55 mF cm−2 is achieved at scan rate at 2 mA cm−2.

We have developed an in situ facile surface oxidation method to fabricate three-dimensional (3D) hierarchical ball of yarn-like CuO microstructures on copper foam, which can be directly used as a long-life binder-free electrode for supercapacitors. The electrochemical results demonstrated that this CuO microstructures exhibited a specific capacitance of 762.55 mF cm−2, excellent cycling stability (98.11% retention after 20000 cycles) and good rate capability (81.5% retention upon increasing the current density by 10 times). These features will make ball of yarn-like CuO microstructures attractive for high-performance supercapacitors.