Facile fabrication and configuration design of Co3O4 porous acicular nanorod arrays on Ni foam for supercapacitors.

The configuration of electrode materials is of great significance to the performance of supercapacitors (SCs) because of its direct effects on specific surface area and electron transfer path. Given this, herein, a series of Co3O4 hierarchical configurations composed of porous acicular nanorods are designedly synthesized on Ni foam with in-site self-organization method depending on the addition of NH4F. In the absence of NH4F, Co3O4 nanorods self-assemble into porous urchin-like structure (PULS), while the introduction of NH4F can induce the vertical growth of Co3O4 acicular nanorods, forming porous acicular nanorod arrays (PANRAs). By simply tuning the concentration of NH4F, the Co3O4 PANRAs with different specific surface area can be obtained. As expected, Co3O4 PANRAs electrode for SCs (using 1 mmol of NH4F) exhibits high specific capacitance (1486 F g-1 at 1 A g-1) and excellent cycling stability (98.8% retention after 5000 continuous charge-discharge cycles), which are better than those of Co3O4 PULS electrode (658.2 F g-1 at 1 A g-1, 90.4%). Corresponding solid-state symmetric SC achieves a high energy density of 48.63 Wh kg-1 at power density of 600 W kg-1. Such superior performance is attributed to fast charge transfer kinetics, facile electron transport and ions diffusion rate resulting from porous array structure, indicating the importance of configuration design of electrode materials for high performance SCs.