Multifunctional materials are vital for enhancing energy storage and conversion technologies. Supercapacitors, with their high power density and rapid charge–discharge capabilities, are essential for electric vehicles and renewable energy systems. Meanwhile, electrocatalysts are essential for promoting electrochemical reactions, including water splitting and fuel cells. By integrating these multifunctional materials, the performance and longevity of electrocatalysts can be significantly improved, resulting in greater energy conversion efficiency. In this context, we synthesized a novel catalyst by first preparing nickel oxide (NiO) through copper (Cu) dealloying, followed by the growth of manganese dioxide (MnO2) nanosheets on nickel foam (MnO2/NiO/NF). In terms of supercapacitor performance, the MnO2/NiO/NF electrode exhibits a specific capacitance of 260.44 F g–1 at 1 A g–1 in a 3.0 M KOH electrolyte. It achieves an energy density of 81.37 W kg–1 at a power density of 1350 W kg–1 and retains 78.5% of its capacitance after 5000 cycles. The MnO2/NiO/NF exhibits exceptional electrocatalytic performance in alkaline environments, achieving overpotentials of 114.00 mV for the hydrogen evolution reaction (HER) and 338.59 mV for the oxygen evolution reaction (OER) at a current density of 10 mA cm–2. The Tafel slopes measured at 113.40 mV dec–1 for HER and 47.70 mV dec–1 for OER indicate the high efficiency of this system. Furthermore, the developed electrolyzer enables complete water splitting at a low cell voltage of 1.57 V while sustaining a current density of 10 mA cm–2. This study highlights the potential of multifunctional materials in enhancing technologies related to energy storage and conversion.

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