Nanostructuring Co3O4 to Tune Capacitive Behaviors: From Low to High Dimensions

Pseudocapacitance is mainly contributed by fast surface-controlled reactions. However, the effect of nanostructures on the capacitive behaviour has not been systematically studied yet. In this work, we synthesize different Co3O4 nanostructures with the same crystal structure and exposed clean crystal planes that include 1D nanowire, 2D nanosheet, 3D rambutan-like and hierarchical structures, ranging from low to high dimensions. It is discovered the specific capacitance of Co3O4 materials follows the order of 1D nanowire > hierarchical structure > 2D nanosheet > 3D rambutan-like structure while the electron transfer resistance is 1D nanowire < 2D nanosheet < hierarchical structure < 3D rambutan-like structure. Under the same electrochemistry, results suggest the pseudocapacitance is not simply dependent on the surface area offered by the nanostructure, but relies on the conductivity, accessibility, diffusion rate and reactivity of the electrode. 1D nanostructure can render the highest reactant accessibility, fastest electron transfer and largest diffusion rate, thus achieving the highest specific pseudocapacitance.