High-specific capacitance, binder-free composite electrodes prepared from carbon dots embedded in copper oxide-nickel oxide nanowires grown on nickel foam for asymmetric supercapacitors

Abstract

The binder-free electrodes based on CuO-NiO and sodium polyacrylate-derived carbon dots (CDs) composites were simply prepared on nickel foam in two steps: hydrothermal synthesis and thermal annealing. A specific capacitance as high as 635 F g⁻¹ (at 5 mV s⁻¹) was achieved with the electrodes containing CDs embedded in the CuO-NiO nanowires, compared to only 468 F g⁻¹ for the CuO-NiO nanowire electrode without CDs, representing a 136 % improvement. To provide mechanistic insights on the supercapacitor performance, electrochemical analysis was carried out, and it was found that synergistic effects from CuO-NiO and CDs gave an optimum contribution of surface/diffusion processes of charge transfer. Asymmetric supercapacitor was also fabricated using activated carbon as a negative electrode and CDs/CuO-NiO@Ni-foam as a positive electrode, giving a 1.5 V, highest energy density of 20.3 Wh kg⁻¹ at power density of 151.1 W kg⁻¹. Due to simplicity and extraordinary performance, the binder-free CDs/CuO-NiO composite electrodes are potential candidates for the mainstream supercapacitors, and the strategy detailed in this work also provides an innovative, practical way for an electrode design for energy storage devices.