Pseudocapacitive Charge Storage in Single-Step-Synthesized CoO–MnO₂–MnCo₂O₄ Hybrid Nanowires in Aqueous Alkaline Electrolytes

A new pseudocapacitive combination, viz. CoO-MnO 2 –MnCo 2 O 4 hybrid nanowires (HNWs), is synthesized using a facile single-step hydrothermal process, and its properties are benchmarked with conventional battery-type flower-shaped MnCo 2 O 4 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 MnCo 2 O 4 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 ∼10 4 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.