Ethanol-assisted hydrothermal synthesis and electrochemical properties of coral-like β-Co(OH)2 nanostructures

Highly uniform, porous β-Co(OH)2 nanostructures with an appearance reminding of certain spherical corals were synthesized via a facile, one-step hydrothermal route using ethanol–water mixtures as solvents. The rough surfaces of the nanostructures consist of numerous randomly distributed, interconnecting nanoflakes, resulting in a network-like structure with many cavities. The coral-like product has a high Brunauer–Emmet–Teller specific surface area of 163 m2/g. The diameter of the coral-like β-Co(OH)2 nanostructures is adjustable from 800 nm to 2 μm. The effects of the ethanol/water ratio, the Co2+ concentration, the hydrothermal temperature, and the reaction time on the formation of the coral-like structures were investigated. Cyclic voltammetry and galvanostatic charge–discharge tests show that the β-Co(OH)2 possesses excellent capacitive properties. This is mainly attributed to the high porosity, which allows a deep penetration by electrolytes.