High‐Capacitance Aqueous Asymmetric Super Capacitor Enabled by Ultrathin Honeycomb‐Like Hierarchical α ‐MnO ₂ @CC Cathode With Remarkable Energy Density

Efficient ultrathin honeycomb‐like nanosheets of α ‐MnO 2 hollandite, decorated on carbon cloth (CC), were successfully synthesized by a one‐pot hydrothermal method. Leveraging the unique tunnel articulated morphology of α ‐MnO 2 , the electrode material exhibited impressive electrochemical performance, achieving a high specific capacitance of 434.46 F g −1 at a current density of 1 A g −1 , exceptional higher value than the previously reports till date, along with exceptional rate capability and excellent stability, evidenced by only 13.1% decay in capacitance after 10 000 cycles at 10 A g −1 . The phase of the synthesized material was confirmed through XRD and XPS analyses. TEM and HR‐TEM imaging revealed the desirable ultrathin nature of the MnO 2 nanosheets on the carbon substrate. When applied in an asymmetric supercapacitor device, the α ‐MnO 2 @CC electrode demonstrated an extended potential window of up to 2.0 V, delivering a remarkable energy density of 57 Wh kg −1 at a power density of 1000 W kg −1 . Notably, it maintained an energy density of 16 Wh kg −1 even at a high‐power density of 20 000 W kg −1 . Consequently, the fabricated cell α‐ MnO 2 @CC//AC demonstrates outstanding electrochemical performance, positioning it as a highly promising candidate for next‐generation supercapacitor applications.