MOF-Assisted Synthesis of Hierarchically Porous ZIF-67-Derived Co3O4 Nanosheets Enabling High Specific Capacitance and Long-Cycle Stability for High-Current-Density Supercapacitors

Abstract

Abstract Herein, ZIF-67 was used as a cobalt-based metal–organic framework precursor to obtain Co 3 O 4 nanosheets due to its uniform cobalt-imidazolate framework and its ability to form porous structures upon thermal decomposition. The ZIF-67-derived Co 3 O 4 nanosheets were synthesized by a hydrothermal method followed by a calcination process. The ZIF-67-derived Co 3 O 4 nanosheets presented pore sizes of 20 nm, 28 nm, and 139 nm and a surface area of 315 m 2 g −1 . The porous nanostructure resulted in a high specific capacitance of 350 F g −1 at 5 A g −1 . Cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) analysis confirmed the electrochemical activity and charge-storage behavior of the material. The charge-transfer resistance is negligible, as indicated by the very small semicircle in the electrochemical impedance spectroscopy plots, confirming high electrical conductivity before and after 5000 cycles. The Co 3 O 4 nanosheet-based electrode material exhibits 95% capacitance retention after 5000 cycles. The redox reactions in the Co 3 O 4 electrode material are dominated by ion diffusion because the b value is close to 0.5, as confirmed by power law calculations. The charge-storage process is dominated (92%) by diffusion, whereas only 8% of the charges are stored by surface processes when analyzed at 50 mV s −1 . The asymmetric device exhibits a capacitance of 156 F g −1 at 1 A g −1 , maximum energy density of 63 Wh kg −1 , maximum power density of 12750 W kg −1 , and 95% cyclic stability after 10,000 cycles. The diffusive and capacitive processes contribute significantly to maximizing charge storage in the Co 3 O 4 electrode material for battery-type supercapacitive devices. Graphical Abstract