ZnO@MnO₂ Core–Shell Nanofiber Cathodes for High Performance Asymmetric Supercapacitors

Abstract

Asymmetric supercapacitors (ASCs) with aqueous electrolyte medium have recently become the focus of increasing research. For high performance ASCs, selection of cathode materials play a crucial role, and core-shell nanostructures are found to be a good choice. We successfully synthesized, ZnO@MnO₂ core-shell nanofibers (NFs) by modification of high-aspect-ratio-electrospun ZnO NFs hydrothermally with MnO₂ nanoflakes. High conductivity of the ZnO NFs and the exceptionally high pseudocapacitive nature of MnO₂ nanoflakes coating delivered a specific capacitance of 907 Fg^-1 at 0.6 Ag^-1 for the core-shell NFs. A simple and cost-effective ASC construction was demonstrated with ZnO@MnO₂ NFs as a battery-type cathode material and a commercial-quality activated carbon as a capacitor-type anode material. The fabricated device functioned very well in a voltage window of 0-2.0 V, and a red-LED was illuminated using a single-celled fabricated ASC device. It was found to deliver a maximum energy density of 17 Whkg^-1 and a power density of 6.5 kWkg^-1 with capacitance retention of 94% and Coulombic efficiency of 100%. The novel architecture of the ZnO@MnO₂ core-shell nanofibrous material implies the importance of using simple design of fiber-based electrode material by mere changes of core and shell counterparts.