The Scanning electron micrograph are carbon nanowalls (CW) formed at Meijo University in Japan by a team of researchers using plasma enhanced chemical vapor deposition. The carbon nanowalls are suitable for use in fuel cell electrodes as catalyst carriers.
Meijo University researchers have created the means and apparatus needed to grow carbon nanowalls in a controlled manner, something which had not been previously achieved.
Among carbonaceous porous materials having a nano-size structure, carbon nanowalls (CNW) are a two-dimensional carbon nanostructure which typically have a wall-like structure in which the walls rise upwards from the surface of a substrate in a substantially uniform direction. Fullerene (such as C60) is a zero-dimensional carbon nanostructure. Carbon nanotubes can be considered to be a one-dimensional carbon nanostructure.
Carbon nanoflakes are an aggregate of planar, two-dimensional, small pieces similar to carbon nanowalls. Like rose petals, the individual small pieces are not connected to each other so that their carbon nanostructure has an inferior directionality with respect to the substrate to that of carbon nanowalls. Thus, carbon nanowalls have a carbon nanostructure with totally different characteristics from fullerene, carbon nanotubes, carbon nanohorns, and carbon nanoflakes.
Although the existence of carbon nanowalls (CNW) and several basic production methods are known by investigators, a method for controlling a structure so as to produce the optimum shape and physical properties of a carbon nanowall (CNW) according to its use and application have until now been unclear.
Dr Mineo Hiramatsu, Professor Department of Electrical & Electronic Engineering. Faculty of Science and Technology, Meijo University, Masaru Hori,. Hiroyuki Kano, Toru Sugiyama, Yuichiro Hama and Hama Yuichiro (Aichi, JP) created the nanofabrication process for controlling a carbon nanowall (CNW) structure, The method results in a material with improved corrosion resistance against high potential by varying the spacing between the carbon nanowall (CNW) walls so that its surface area and crystallinity are controlled.
Also provided is a carbon nanowall (CNW) with a high surface arca and a carbon nanowall (CNW) with a high crystallinity, both of which have a controlled structure. A carbon nanowall is then formed by PECVD (plasma enhanced chemical vapor deposition).
FIG. 1 illustrates a schematic view of one example of an apparatus for forming a carbon nanowall having a controlled structure according to the Meijo scientists. Hydrogen radicals as well as a reaction gas (carbon source gas) containing carbon, such as CF4, C2F6, or CH4, are introduced between parallel plate electrodes in the chamber illustrated in FIG. 1.
The reaction chamber is provided with a parallel plate capacitively coupled plasma (CCP) generating mechanism which includes a first electrode and a second electrode . In this way, electromagnetic waves such as RF waves are irradiated to form a plasma atmosphere in which the source gas has been turned into plasma.
On the other hand, in a radical generating chamber provided externally to the reaction chamber , a radical source gas containing at least hydrogen is decomposed by RF waves or the like to generate hydrogen radicals . The hydrogen radicals are injected into the plasma atmosphere, and carbon nanowalls form on the surface of a substrate arranged on the second electrode.
The nanofabrication process is disclosed in detail in U.S. Patent Application 20100009242
By varying the ratio between the introduction rates of the process gases in a carbon nanowall (CNW) production process by plasma CVD, the spacing between the carbon nanowall (CNW) walls can be varied, which allows the surface area and crystallinity to be controlled.
The carbon nanowall has an increased amount of supported catalyst because of its large surface area, as well as high conductivity and excellent corrosion resistance against high potential because of its high crystallinity, and is thus especially suitable as an electrode catalyst carrier for a fuel cell.
