High-voltage and high-rate symmetric supercapacitor based on MnO2-polypyrrole hybrid nanofilm

A manganese oxide (MnO2) nanosheet film, hybridized with a conducting polymer polypyrrole (PPy), was prepared through the direct reaction of a carbon cloth with potassium permanganate (KMnO4) and through the subsequent chemical polymerization; this type of prepared nanosheet has been used as an electrode for symmetric supercapacitors. The influence of the reaction time in the KMnO4 solution on the capacitive property of the MnO2 film was systematically investigated. Further experimentation revealed that the PPy with the high electrical conductivity had promoted the charge transfer in the MnO2 nanofilm and had played an important role in enhancing the electrode performance (∼45.6 mF cm−2). An areal capacitance of 25.9 mF cm−2 and an excellent rate performance (∼50.08% of the initial capacitance when the scan rate increases 100 times from 2.5 to 250 mV s−1) can be achieved for an aqueous symmetric supercapacitor that is assembled from the MnO2-PPy nanofilm. In particular, an operating voltage of 1.2 V can be delivered by choosing an appropriate electrolyte; this voltage level is much larger than that of traditional aqueous symmetric supercapacitors (⩽1.0 V) and contributes to a high energy density (∼3.5 μWh cm−2). Under such a high output voltage, the device can still maintain ∼86.21% of the initial capacitance, even after 2000 cycles.