Cubic spinel AB₂O₄ Type Porous ZnCo₂O₄ Microspheres: Facile hydrothermal synthesis and their electrochemical performances in pseudocapacitor

Microspheres of cubic spinel ZnCo₂O₄ were synthesized using a facile ethylene glycol-mediated hydrothermal method. The size and crystallinity of the ZnCo₂O₄ microspheres were tuned by simply varying the reaction times. The as-synthesized ZnCo₂O₄ microspheres had porous structures that were constructed by numerous small building blocks of primary nanoparticles, leading to the formation of sphere-like morphology. The ZnCo₂O₄ microspheres exhibited a large surface area of 37.27 m² g^-1 with mesopores, 24.66 nm in size, resulting in significantly enhanced electrochemical activity toward pseudocapacitors. Remarkably, the as-made ZnCo₂O₄ 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 ZnCo₂O₄ microsphere electrodes achieved an energy density of 11.8 Wh kg^-1 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.