Significant enhancement of the electrochemical performance of hierarchical Co3O4 electrodes for supercapacitors via architecture design and training activation

Abstract

Binder-free Co3O4 electrodes with hierarchical structures, nanoflowers and nanowire network, were directly grown on nickel foams with a facile hydrothermal strategy and subsequent annealing treatment. The architectures of the electrodes, flowers- or nanowires-dominated, can be selectively synthesized by simply controlling the reaction time of hydrothermal synthesis. It is clarified that the nanoflowers with mesoporous petals were constructed by the assembly of nanowires, resulting in the flowers-dominated Co3O4 electrode exhibiting enhanced electrochemical performance: including high specific capacitance (2.266 and 1.91 F cm−2 at 1 and 10 mA cm−2, respectively), remarkable rate capability and superior cycle stability. A cyclic voltammetry (CV) training technique was proposed to explore the full energy storage potential of Co3O4 electrode material for supercapacitors; after trained over 200 CV cycles at the scan rate of 5 mV s−1, the specific capacitance of the flower-dominated electrode further enhanced from 2.266 to 4.472 F cm−2 at current density of 1 mA cm−2, coupled with excellent electrochemical performance: rate capability (80.3% capacity retention at 10 mA cm−2) and cycle stability (84.6% capacitive retention over 5000 GCD cycles). An asymmetric supercapacitor (ASC) was constructed by employing flower-dominated Co3O4 as positive electrode and activated carbon as negative electrode. The ASC device delivered a high energy density of 0.215 mWh cm−2 at a power density of 1.49 mW cm−2. This encouraging result reveals that the flower architecture is acceptable for electrode material and provides a highly efficient training process to significantly enhance the electrochemical performance for supercapacitors.