Ultrathin Mesoporous RuCo 2 O 4 Nanoflakes: An Advanced Electrode for High‐Performance Asymmetric Supercapacitors

A new ruthenium cobalt oxide (RuCo 2 O 4 ) 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 2 O 4 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 −1 at 6 A g −1 ) 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 2 O 4 (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 (1.1 mWh cm −3 ). More importantly, the cell delivered an energy density of 12.4 Wh kg −1 even at a maximum power density of 3.2 kW kg −1 , which is noticeably superior to carbon‐based symmetric systems.