Pseudocapacitive charge storage in single-step-synthesized CoO-MnO2-MnCo2O4 hybrid nanowires in aqueous alkaline electrolytes

A new pseudocapacitive combination, viz. CoO-MnO2-MnCo2O4 hybrid nanowires (HNWs), is synthesized using a facile single-step hydrothermal process, and its properties are benchmarked with conventional battery-type flower-shaped MnCo2O4 obtained by similar processing. The HNWs showed high electrical conductivity and specific capacitance (Cs) (1650 F g-1 or 184 mA h g-1 at 1 A g-1) with high capacity retention, whereas MnCo2O4 nanoflower electrode showed only one-third conductivity and one-half of its capacitance (872 F g-1 or 96 mA h g-1 at 1 A g-1) when used as a supercapacitor electrode in 6 M KOH electrolyte. The structure-property relationship of the materials is deeply investigated and reported herein. Using the HNWs as a pseudocapacitive electrode and commercial activated carbon as a supercapacitive electrode we achieved battery-like specific energy (Es) and supercapacitor-like specific power (Ps) in aqueous alkaline asymmetric supercapacitors (ASCs). The HNWs ASCs have shown high Es (90 Wh kg- ) (volumetric energy density Ev 0.52 Wh cm- ) with Ps up to ~104 W kg-1 (volumetric power density Pv 5 W cm-3) in 6 M KOH electrolyte, allowing the device to store an order of magnitude more energy than conventional supercapacitors. © 2017 American Chemical Society.