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.