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 (C s) (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 (E s) and supercapacitor-like specific power (P s) in aqueous alkaline asymmetric supercapacitors (ASCs). The HNWs ASCs have shown high E s (90 Wh kg–1) (volumetric energy density E v ≈ 0.52 Wh cm–3) with P s up to ∼104 W kg–1 (volumetric power density P v ≈ 5 W cm–3) in 6 M KOH electrolyte, allowing the device to store an order of magnitude more energy than conventional supercapacitors.