Biomass‐Derived Activated Carbon Microtubes From Butea monosperma Flowers and Hydrothermally Grown Triple‐Morphological Co ₃ O ₄ Electrodes in Flexi

The fabrication of an energy storage device with high energy and power densities is highly demanding for advanced energy storage systems for commercial applications. The asymmetric hybrid supercapacitor device is a promising configuration to increase both energy and power densities using the battery‐type (cathode) and EDLC‐type (anode) electrode materials. In this work, the hydrothermally synthesized cobalt oxide (Co ₃ O ₄ ) samples are calcined at different temperatures 300 °C (named as CO3), 400 °C (CO4), and 500 °C (CO5) for 2 h. The X‐ray diffraction results confirm the cubic phase of the Co ₃ O _4, and the field‐emission scanning electron microscopic (FE‐SEM) study reveals the unique triple morphology of the electrode CO5 (Co ₃ O ₄ calcined at 500 °C). The cyclic voltammetry studies reveal that the triple‐morphological Co ₃ O ₄ (CO5) electrode shows battery‐like behavior in the KOH electrolyte and exhibiting a high specific capacity of 546 C/g at a current density of 1 A/g due to the increased redox‐active sites of the electrode. On the other hand, the biomass‐derived activated carbon (BAC) from Butea monosperma flowers (BMF) confirms the formation of a microtube‐like structure by the FE‐SEM studies. Consequently, an asymmetric flexible supercapattery (FSC) device was fabricated using the better‐performing triple‐morphological Co ₃ O ₄ (CO5) electrode as the cathode and the BAC electrode as the anode, exhibiting a significantly higher specific capacity of 239 C/g at 1 A/g with high energy density (39.83 Wh/kg) and power density (560 W/kg). The excellent electrochemical performance of the FSC device holds significant potential as an advanced energy storage solution for flexible and wearable electronics.