Indexed on: 27 Oct '17Published on: 27 Oct '17Published in: ACS Applied Materials & Interfaces
Manganese oxides (MnO2) are regarded as typical and promising electrode materials for supercapacitors. However, the practical electrochemical performance of MnO2 is far from its theoretical value. Nowadays, numerous efforts are devoted to the design and preparation of nano-structured MnO2, with the aim of improving its electrochemical properties. In this work, ultra-long MnO2 nanowires were fabricated induced by carbon quantum dots (CQDs); subsequently, a binder-free flexible electrode membrane was easily obtained by vacuum filtration of MnO2 nanowires. It was found that the carbon quantum dots did not only induce the formation of 1D nanostructure MnO2, but also significantly improved the wettability between electrode and electrolyte. In other words, the MnO2 membrane demonstrated a superhydrophilic character in aqueous solution, indicating the sufficient and abundant contact probability between electrode material and electrolyte solution. The binder-free flexible MnO2 electrode exhibited a preeminent specific capacitance of 340 F g-1 at 1 A g-1; even when the current density reached 20 A g-1, it still maintained 260 F g-1 (76% retention rate compared to 1 A g-1). Moreover, it also showed good cycling stability with 80.1% capacityretention over 10,000 cycles at 1 A g-1. Furthermore, an asymmetric supercapacitor device was constructed using a MnO2 membrane and active carbon as the positive and negative electrodes, respectively, which exhibited a high energy density of 33.6 Wh kg-1 at 1.0k W kg-1, and a high power density of 10k W kg-1 at 12.5 Wh kg-1. The above results indicate the great potential of CQD-induced MnO2 as a high-performance active material for supercapacitors.