Supercapacitive Properties of Hydrothermally Synthesized Co₃O₄ Nanostructures

A hydrothermal process was employed to create a variety of Co 3 O 4 nanostructures. We demonstrate that nominally minor differences in the synthesis temperature (50, 70°, or 90 °C) yield profound variations in the oxide microstructure, with lath-like, necklace-like and net-like morphologies of different scales resulting. This in turn resulted in significant variations in the supercapacitive performance that ranged from mediocre to superb. Specifically, the mesoporous net-like Co 3 O 4 nanostructures that were synthesized at 50 °C exhibited very favorable electrochemical properties: The net-like Co 3 O 4 had a specific capacitance of 1090 F/g at a mass loading of 1.4 mg/cm 2 . At this high mass loading, such performance has not been previously reported. SEM and TEM analysis of these samples revealed an interconnected array of sub-10 nm crystallites interspersed with a high volume fraction of similar scale pores. The poorer performing microstructures were both coarser and much less porous.