Temperature driven high-performance pseudocapacitor of carbon nano-onions supported urchin like structures of α-MnO₂ nanorods

The promising pseudocapacitive charge storage insists the strategic design of three-dimensional architecture of nanostructures with extra-active redox sites on and/or near surface with high capacity of ionic insertion into the porous network of electrodes. Herein, we report the urchin like structure of α-MnO₂ nanorods grown on carbon nano-onion (CNO) support via simple, cost-effective wet chemical method. The highly crystalline α-MnO₂ nanorods with larger spinel sizes of 0.46 nm and 0.18 nm are characterized by SEM, TEM, XRD and Raman spectra. These spinel structures of α-MnO₂ nanorods offers large cavity for ions insertion, which further improved by increasing temperature due to fast ionic mobility. The temperature driven increment of specific capacity from 202 Cg^-1 to 363 Cg^-1 at current density 0.3 Ag^-1 is accomplished owing to the improved ionic conductivity, surface area and fast charge transfer. Further the 78% capacitance retention after 1000 cycles at 70 °C is realized, which is just 17% lower that the cyclic stability at 4 °C. It emphasizes an importance of three-dimensional design/architecture of electrode materials for the high-temperature pseudocapacitor applications.