Engineering Ultrathin Co(OH)2 Nanosheets on Dandelion–like CuCo2O4 Microspheres for Binder‐Free Supercapacitors

Abstract A stepwise synthetic approach is developed for large‐scale growth of three‐dimensional branched CuCo 2 O 4 @Co(OH) 2 core−shell structures on nickel foam as a high‐performance supercapacitor electrode. The synthesis procedure involves the hydrothermal treatment of a bimetallic (Cu, Co) hydroxide precursor on a Ni foam substrate and subsequent thermal transformation to dandelion‐like CuCo 2 O 4 microspheres. The Co(OH) 2 shells are then coated onto the branches of as‐prepared CuCo 2 O 4 microspheres by using an electrodeposition method. The loading of Co(OH) 2 nanosheets is dependent on the electrodeposition time in Co(NO 3 ) 2 solution. The resulting unique core−shell structure promotes fast electron and ion transport, large electroactive surface area, and excellent structural stability. As a result, superior electrochemical performance is achieved with a specific capacitance of 424 F g −1 at a current density of 0.5 A g −1 , and good cycling performance (85.8 % retention after 10000 cycles), suggesting its promising application in supercapacitors. These good electrochemical properties could be attributed to the synergic interaction of each component. In addition, the asymmetric supercapacitor exhibits an energy density of 19.2 Wh kg −1 at a power density of 350 W kg −1 .