Ultrathin Mesoporous RuCo O Nanoflakes: An Advanced Electrode for High-Performance Asymmetric Supercapacitors.

A new ruthenium cobalt oxide (RuCo O ) with a unique marigold-like nanostructure and excellent performance as an advanced electrode material has been successfully prepared by a simple electrodeposition (potentiodynamic mode) method. The RuCo O marigolds consist of numerous clusters of ultrathin mesoporous nanoflakes, leaving a large interspace between them to provide numerous electrochemically active sites. Strikingly, this unique marigold-like nanostructure provided excellent electrochemical performance in terms of high energy-storage capacitance (1469 F g at 6 A g ) with excellent rate proficiency and long-lasting operating cycling stability (ca. 91.3 % capacitance retention after 3000 cycles), confirming that the mesoporous nanoflakes participate in the ultrafast electrochemical reactions. Furthermore, an asymmetric supercapacitor was assembled using RuCo O (positive electrode) and activated carbon (negative electrode) with aqueous KOH electrolyte. The asymmetric design allowed an upgraded potential range of 1.4 V, which further provided a good energy density of 32.6 Wh kg (1.1 mWh cm ). More importantly, the cell delivered an energy density of 12.4 Wh kg even at a maximum power density of 3.2 kW kg , which is noticeably superior to carbon-based symmetric systems.