Bifunctional Electrochemical Behavior of S‐rGO@GO/MnO ₂ for Advanced Supercapacitor and Lithium‐Ion Hybrid Capacitor

In pursuit of advanced and efficient energy storage technologies, the development of multifunctional electrode materials that can deliver superior performance across various platforms has become a focal point nowadays. In this context, the present work demonstrates the in situ synthesis and comprehensive electrochemical evaluation of a sulfonated reduced graphene oxide anchored on a graphene oxide/manganese dioxide hybrid nanostructure S‐rGO@GO/MnO ₂ (SGM), as a versatile electrode for both supercapacitor and lithium‐ion hybrid capacitor (LIHC). By strategically combining the high electrical conductivity, large surface area, and mechanical robustness of graphene‐based materials with the intrinsic pseudocapacitive properties of MnO ₂ , the hybrid nanostructure achieves a synergistic enhancement in electrochemical performance. When used as an electrode in a symmetric supercapacitor with an aqueous electrolyte, the SGM electrode exhibits a high total device capacitance of 109 F g ⁻¹ , along with excellent rate capability and cycling stability up to 10 000 cycles, making it well‐suited for high‐power applications. In the case of LIHC, the same hybrid nanostructure, when evaluated as an anode in a half‐cell, exhibits a high specific capacity of 725 mAh g ⁻¹ at 0.1 A g ⁻¹ and retains 340 mAh g ⁻¹ even at a high current density of 1.5 A g ⁻¹ . Upon appropriate mass balancing and prelithiation, this anode is paired with porous carbon, which acts as the cathode, resulting in a full‐cell LIHC that achieves an impressive energy density of 80 Wh kg ⁻¹ and a peak power density of 3.75 kW kg ⁻¹ , with good cycling stability. This dual functionality across different energy storage systems underscores the versatility and robustness of the SGM hybrid nanostructure, positioning it as a promising candidate for next‐generation hybrid energy storage devices.