Branched Carbon Nanotubes Used to Create Improved Fuel Cell Electrode by Samsung Scientists

Samsung scanning electron microscopic (SEM) photograph showing the uniform distribution of metallic carbon particles over a carbon substrate;  and the lower image  is a SEM photograph of carbon nanotubes for use in fuel cells .  

Samsung  SDI Co., Ltd. (Suwon-si, KR) scientists describe a method of manufacturing carbon nanotubes for use in a fuel cell and an improved polymer fuel cell using the carbon nanotubes for its electrode in U. S. Patent Application 20100018851. The electrode is applicable to both hydrogen and methanol polymer electrolyte fuel cells.

The internal and external walls of the carbon nanotubes are doped with nano-sized metallic catalyst particles uniformly to a degree of 0.3-5 mg/cm². The carbon nanotubes are grown over a carbon substrate using chemical vapor deposition or plasma enhanced chemical vapor deposition. Since the carbon nanotubes have a large specific surface area, and metallic catalyst particles are uniformly distributed over the internal and external walls thereof, the reaction efficiency in an electrode becomes maximal when the carbon nanotubes are used for the electrode of a fuel cell.

The carbon nanotubes fabricated using the method can be applied to form a large electrode. The carbon nanotubes grown over the carbon substrate can be readily applied to an electrode of a fuel cell, providing economical advantages and simplifying the overall electrode manufacturing process. A fuel cell using as the carbon nanotubes for its electrode provides improved performance, say Samsung inventors Won-bong Choi,  Jae-uk Chu, Chan-ho Park and  Hyuk Chang

Recently, with growing concerns about the environment and the exhaustion of energy resources, and the commercialization of fuel cell automobiles, there is an urgent need for the development of reliable, high-performance fuel cells that are operable at an ambient temperature with high energy efficiency and for the development of polymer membranes capable of increasing the efficiency of fuel cells

The researchers also developed a method for fabricating carbon nanotubes grown over a carbon substrate. The process includes: uniformly distributing metallic catalyst particles over the carbon substrate; and supplying a carbon source gas at a constant rate under atmospheric pressure and reacting the carbon source gas with the metallic catalyst particles at a temperature of 400-900 for 1-120 minutes to grow carbon nanotubes over the carbon substrate.

Electrodes, fuel, electrolyte membranes for high energy density, high power fuel cells have been actively researched. In addition, there have been attempts to increase the activity of a catalyst used in the electrodes. Since the activity of catalysts is proportional to the reaction surface area thereof, it is necessary to increase the reaction surface area by reducing the diameter of catalyst particles to a few nanometers and to uniformly distribute such nano-sized catalyst particles over the electrodes.

Samsung scanning electron microscopic (SEM) photograph showing the uniform distribution of metallic carbon particles over a carbon substrate;  and the lower image is a SEM photograph of carbon nanotubes for use in fuel cells .

FIG. 4 is a transmission electron microscopic (TEM) photograph of a branched carbon nanotube for use in fuel cells manufactured by Samsung.

FIG. 6 illustrates., step by step, a method for fabricating carbon nanotubes according to the inventors, in which (a) illustrates uniformly distributing catalyst particles over a carbon substrate, (b) illustrates directly growing carbon nanotubes over the carbon substrate with the catalyst particles serving as seeds for the growth of the carbon nanotubes, (c) illustrates adjusting the density of growing carbon nanotubes, and (d) illustrates adjusting the growth of carbon nanotubes to form branched carbon nanotubes.