Cubic Spinel AB₂O₄Type Porous ZnCo₂O₄Microspheres: Facile Hydrothermal Synthesis and Their Electrochemical Performances in Pseudocapacitor

Microspheres of cubic spinel ZnCo 2 O 4 were synthesized using a facile ethylene glycol-mediated hydrothermal method. The size and crystallinity of the ZnCo 2 O 4 microspheres were tuned by simply varying the reaction times. The as-synthesized ZnCo 2 O 4 microspheres had porous structures that were constructed by numerous small building blocks of primary nanoparticles, leading to the formation of sphere-like morphology. The ZnCo 2 O 4 microspheres exhibited a large surface area of 37.27 m 2 g −1 with mesopores, 24.66 nm in size, resulting in significantly enhanced electrochemical activity toward pseudocapacitors. Remarkably, the as-made ZnCo 2 O 4 microspheres electrode delivered a high specific capacitance (853.6 F g −1 at a current density of 2 A g −1 ), good rate performance (417.1 F g −1 at 10 A g −1 ) and excellent cyclic stability (92.7% capacitance retention after 3000 cycles at a current density of 10 A g −1 ). Moreover, a symmetric supercapacitor based on ZnCo 2 O 4 microsphere electrodes achieved an energy density of 11.8 Wh kg −1 and a maximum power density of 2.5 kW kg −1 . The good electrochemical performances can be attributed to the unique porous microsphere texture, high surface area and good electrical conductivity due to the synergistic effect between the two metal elements.