Hierarchical Nanoporous Carbons with an Integrated Activation Using 3D Flower‐Like ZnO Microspheres and KOH for Flexible EDL Capacitor with a High Operating Potential

Abstract Activated nanoporous carbons are widely used in various applications, where their efficiency is largely determined by their specific surface area and pore structure. Traditional KOH‐assisted chemical activation methods primarily produce micropores, limiting the performance of these porous carbons in applications requiring a hierarchical arrangement of micro, meso, and macropores. This study introduces a novel integrated activation strategy using 3D flower‐like microsphere (3DFM) ZnO and KOH to synthesize nanoporous carbons from Sesbania Grandiflora side shoots. The porous nanosheet tips and microsphere bulk of 3DFM‐ZnO generate mesopores and macropores, while KOH induces microporosity, resulting in a hierarchical structure with an ultrahigh specific surface area of 4114 m 2 g −1 . The fabricated activated carbon electrodes with the combination of macro, meso, and micropores exhibit high specific capacitances of 672 F g −1 for the positive electrode and 756 F g −1 for the negative electrode. The performance of electrodes is optimized with the proper selection of electrolytic ions for positive and negative electrodes. A high operating potential window of 2.7 V is achieved in a symmetric device through charge‐balanced mass loading. The fabricated flexible electric double‐layer capacitor demonstrates a maximum specific energy of 128.2 W h kg −1 at a specific power of 1.35 kW kg −1 .