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The potential window for aqueous supercapacitor cathodes greatly depends on the electrochemical stability of water, and thus is generally limited to ∼1.2 V. Herein, a 1.4 V potential window (vs Ag/AgCl) in the 5 M NaNO 3 aqueous electrolyte for porous δ-MnO 2 with a hierarchical interconnected nanosheet structure grown on electrochemically roughened graphite paper by electrodeposition is reported. A specific capacitance of ∼407.6 F g −1 is delivered at 1 A g −1 , and capacitance retention up to ∼90.7% is achieved after 5000 cycles at 8 A g −1 . The aqueous asymmetric supercapacitors of 2.4 V are assembled with the configuration of δ-MnO 2 //activated carbon, and an energy density (E) of ∼38.4 Wh kg −1 is obtained at 599.7 W kg −1 (even at 12 kW kg −1 , E of ∼21.7 Wh kg −1 is still delivered). Moreover, the asymmetric supercapacitors exhibit good rate and cycling performance. Thanks to the simple preparation for the electrode materials/structures and high device performance, it is believed that this work provides valuable contributions to developing aqueous supercapacitors delivering a broad working voltage window and thus an elevated energy density.

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