Femtosecond Laser-Induced Copper Oxide Nanospheres on Copper Foam Surfaces

A facile and scalable strategy is presented in this work for the direct fabrication of binder-free copper (Cu) oxide nanospheres on the Cu foam surface via femtosecond (fs) laser ablation for energy storage applications, primarily in supercapacitors. XRD and EDX analyses confirmed the presence of Cu oxides. At the same time, SEM images indicated that the resulting Cu oxide nanospheres range from ~70 to 700 nm in size, with hierarchical surface features such as laser-induced periodic surface structures (LIPSS), which provide additional active sites for reversible redox reactions. The prepared fs laser-ablated Cu foam samples, with Cu oxide nanospheres (Femto-Cu), can store 8 to 10 times more energy than the bare Cu foam, with ~87.7% capacitance retention after 10,000 charging–discharging cycles. Further, in-depth kinetic investigations revealed that the charge is stored through both surface-controlled capacitive behavior and a diffusion-controlled mechanism. These findings highlight the effectiveness of fs laser-induced structuring in improving the charge-storage characteristics of Cu foam and provide a promising route for developing high-performance, binder-free electrodes in a single step.