Enhancing redox-active interfaces in Cu₂O via controlled surface sulfurization for advanced energy storage devices

The development of highly efficient electrode materials for the next generation of supercapacitors remains a key challenge despite its importance for enhancing energy storage capacity by maintaining power delivery and cycling stability. This study employed a simple sulfurization strategy for modifying electrodeposited Cu₂O on nickel foam (NF), turning a surface into a hybrid structure comprised of additional CuO and CuS phases. This modification improved electrochemical performance by increasing charge storage and facilitating quick electron and ion transport. The sulfurized Cu₂O-S electrode has shown to have a very high electrochemical surface area of 1014.11 cm² as compared with pristine Cu₂O (371.48 cm²) and bare NF (76.10 cm²). Furthermore, it demonstrated good cyclic stability, retaining ~85 % of the capacitance after 20,000 charge-discharge cycles at 20 mA cm⁻². To evaluate the practical feasibility, we assembled an asymmetric supercapacitor device (ASD) using Cu₂O-S and activated carbon (AC) as the positive and negative electrodes, respectively. The ASD demonstrated an energy density of 0.15 mWh cm⁻² at a power density of 3.75 mW cm⁻² along with a cyclability retention of ~80 % over 12,000 cycles. Post-cycling characterization confirmed the structural integrity of the electrode as XPS and SEM analysis showed moderate surface oxidation and increased roughness that may have contributed to sustaining the electrochemical activity. Overall, this study establishes sulfurization as a simple and effective approach for enhancing the energy storage performance of Cu₂O-based electrodes in supercapacitor applications.