A Hierarchical Interconnected Nanosheet Structure of Porous δ-MnO2 on Graphite Paper as Cathode with a Broad Potential Window for NaNO3 Aqueous Electrolyte Supercapacitors

The potential window for aqueous supercapacitor cathodes greatly depends on the electrochemical stability of water, and thus is generally limited to similar to 1.2 V. Herein, a 1.4 V potential window (vs Ag/AgCl) in the 5 M NaNO3 aqueous electrolyte for porous delta-MnO2 with a hierarchical interconnected nanosheet structure grown on electrochemically roughened graphite paper by electrodeposition is reported. A specific capacitance of similar to 407.6 F g(-1) is delivered at 1 A g(-1), and capacitance retention up to similar 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 delta-MnO2//activated carbon, and an energy density (E) of similar to 38.4 Wh kg(-1) is obtained at 599.7 W kg(-1) (even at 12 kW kg(-1), E of similar to 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.