Pores for thought

Porous cobalt oxide nanowires can be grown on a range of conducting substrates

Credit: © 2006 ACS

The unique electrochemical properties of cobalt oxide make it an important material for a range of applications. Now, researchers at Ohio State University in the USA have shown how hollow nanowires made of porous Co₃O₄ can be grown directly onto conducting substrates.

Yiying Wu and co-workers¹ made nanowires that contained both cobalt hydroxide and Co₃O₄ by immersing the substrate in a hot solution of cobalt nitrate and concentrated ammonia. These nanowires were then converted into pure single-crystal Co₃O₄ nanowires by heating them. Scanning electron microscope images showed that the nanowires were hollow, approximately 500 nm in diameter and up to 15 μm long. They were also porous, with pore sizes of 3–4 nm. The nanowires were grown on a variety of substrates including silicon, transparent conducting glass and copper foil. Furthermore, it was possible to pattern the substrate, covering parts of it with gold and therefore preventing nanowire formation in these areas.

The ability to make good electrical contact with conducting substrates, combined with a high surface area, means that the nanowires could prove useful for applications such as lithium-ion batteries, gas sensing and electrochromic devices.