First discovered in 1999, like Carbon Nanotubes they exhibit the same graphitic carbon structure and are now being produced in large quantities.
Carbon nanohorns
Carbon Nanohorns (CNH) were first discovered in Japan in 1999 by Prof. Iijima and colleagues. Like Carbon Nanotubes they exhibit the same graphitic carbon structure. Single-walled nanohorns (SWNHs) are made of 2-20 nm wide and 25 to 150 nm long tubes which are closed at one end by a cone – the most appropriate shape comparison would be that of a nano-sized sewing thimble. The CNH aggregate to form agglomerates (secondary particles) of about 100 nm to µm size.
Figure 1: Carbon nanohorns schematic.
Carbon nanohorns have found application in proton exchange membrane (PEM) and Polymer Electrolyte (PEFC) fuel cells because they have the duel capability of providing a high surface area conductive layer and open gas paths. They are available from a number of companies including Reade Materials (www.reade.com) in single walled, double walled and multi-walled forms, bundled and unbundled.
Nanohorns can be manufactured by several methods. US company NanoCraft, Inc (www.nanocraftinc.com) uses protected proprietary and patent pending high volume production methods. The resulting nanohorns are 2 to 3 nm in diameter and 30 to 50 nm in length with a 19 degree closed end called a horn. They form into a cluster with a diameter of about 30 to 120 nm. Applications for nanohorns include gas absorption, filtration, lubrication, super-capacitors, coatings, storage of methane, biomedical, field emission, adhesives, composites, biosensing, drug delivery, gas storage and the aforementioned catalyst supports for fuel cells. In cooperation with TIE GmbH. EEnanoTech (www.eenanotech.co.jp) has developed an industrial production process for Carbon Nanohorns (CNH).
Figure 2: Carbon nanohorns (Nanocraft, Inc.)
In January 2013, NEC Corporation (www.nec.com/en/global/prod/cnh) announced the availability of carbon nanohorns, with a production capacity of 1KG of 95% pure carbon nanohorns. Since carbon nanohorns can be efficiently produced using simple methods (Pulsed Laser Ablation) at room temperature and under normal atmospheric conditions, they can be provided at a low cost when compared to the cost of other nano carbon materials that are complicated to produce. Pulsed Laser Ablation Method produces carbon nanohorns where a graphite target (mass of carbon) is irradiated with a strong CO2 laser. This makes it possible to easily produce high-purity carbon nanohorns at room temperature.
