| Summary: | In this work, a birnessite-type MnO2/carbon composite with hierarchical nanostructures was synthesized using KMnO4 solution and spent printing carbon grains. A hybrid electrochemical supercapacitor device was fabricated based on the birnessite-type MnO2–carbon composite electrode and carbonized iron-polyaniline/nickel graphene foam as positive and negative electrodes, respectively. At the lowest specific current of 1.0 A g−1 and cell potential of 2.2 V in 2.5M KNO3 electrolyte, the device displayed a high energy and power density of 34.6 W h kg−1 and 1100.0 W kg−1, respectively. The device further displayed long-term cycling stability with a capacitance retention of 98% over 10 000 galvanostatic charge–discharge cycles at 10 A g−1. This device displays the overall excellent electrochemical performance.
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