Engineering NiO/g-C₃N₄ and NiO/rGO composites for dual applications in electrochemical water splitting and energy storage.

The development of multifunctional electrode materials that can simultaneously serve as efficient electrocatalysts and high-performance energy storage devices is highly desirable for next‐generation energy conversion technologies. In this work, we report a facile hydrothermal strategy followed by annealing at 400 °C, which enables the in-situ reduction of GO to rGO without external reducing agents, leading to robust NiO/rGO and NiO/g-C₃N₄ nanocomposites. This approach ensures intimate interfacial contact between NiO and the conductive carbon matrix, thereby enhancing charge transfer and catalytic activity. The composites were systematically characterized using XRD, BET, Raman, FESEM–EDX, XPS, and TEM analyses to confirm structural and surface features. Electrochemical evaluation revealed that NiO/rGO and NiO/g-C₃N₄ electrodes delivered low overpotentials of 126 and 73 mV at 10 mA cm⁻² for HER in 1 M KOH, with NiO/g-C₃N₄ exhibiting long-term stability over 23 h. As supercapacitor electrodes, NiO/rGO and NiO/g-C₃N₄ achieved remarkable specific capacitances of 597 and 366 F g⁻¹ at 1 A g⁻¹, respectively, surpassing many previously reported NiO–carbon systems. These results demonstrate that the unique synthesis route and synergistic coupling of NiO with conductive carbon frameworks enable a substantial advancement in multifunctional electrode design, offering a promising pathway for integrated energy conversion and storage systems.