NEC uses Carbon Nanotubes to Develop a Tiny Fuel Cell - News Item

NEC Corporation, the Japan Science and Technology Corporation and the Institute of Research and Innovation today announced they have developed a tiny fuel cell for mobile terminals using the much anticipated carbon technology raw material - carbon nanotubes - as electrodes, confirming the fuel cell characteristic is much improved compared with conventional type, which uses activated carbon. This result was attained by using the minute and unique structure of the "carbon nanohorn", which is one type of the carbon nanotube. The fuel cell has about 10-times the energy capacity compared with a lithium battery, and if used for personal computers, in the future, a continued usage time of several days can be expected.

The fuel cells, which directly transform the chemical reaction energy between hydrogen and oxygen into electric energy, are seen as the energy source of the next- generation. With their environmentally friendly and high efficiency characteristics the cells are being researched and developed as the future energy for the automobile and as energy generation for the home. The energy capacity is expected to become at least 10 times that of the present highest density lithium secondary battery, used in a wide range of applications. This new technological development is expected to solve the currently faced problems of dramatically reducing power consumption rates and is one big step towards achieving a practical fuel cell for mobile terminals.

Carbon nanotubes are a completely new carbon system material, which were discovered by one of NEC's Research Fellows, Sumio Iijima in 1991, and are expected become the typical raw material for nano-technology, applied to such broad fields as, hydrogen storage, composite materials and electron devices. This time, the research group, focusing on the detailed structure of the carbon nanotube examined the possibility of applying it to fuel cell electrodes, confirming that the nanotube has the possibility of clearly surpassing raw materials used to date.

The carbon nanotubes used for the experimental manufacturing are named nanohorns due to their irregular horn-like shape, and were discovered three years ago by Dr. Sumio Iijima's research group. Nanohorns have the same graphitic carbon atom structure as normal carbon nanotubes. The main characteristic of the carbon nanohorns is that when many of the nanohorns group together an aggregate (a secondary particle) of about 100 nanometers is created. The advantage being, that when used as an electrode for a fuel cell, not only is the surface area extremely large, but also, it is easy for the gas and liquid to permeate to the inside. In addition, compared with normal nanotubes, because the nanohorns are easily prepared with high purity it is expected to become a low-cost raw material.

The developed tiny fuel cell, classified as a polymer electrolyte fuel cell (PEFC), utilizes the carbon nanohorns as electrodes for catalyst support. It is observed that very fine platinum catalyst particles are dispersed on the surfaces of the carbon nanohorns. The size of the platinum particle is less than half of that supported on the ordinary activated carbon (acetylene black) by the same method. The size of the catalyst particle is one of the most important factors that determine the performance of the fuel cell, and it is considered that, the finer the size the better performance.

Although the reason a catalyst particle becomes fine is still not clear in the case of the carbon nanohorn, because of the unique shape of the aggregate it is thought that contact and grain growth of catalyst particles will be prevented. It is also expected that by further altering the form of the carbon nanohorn the dispersed state and the battery characteristic of the catalyst particle will improve. In addition, because a carbon nanohorn is produced by the laser ablation method, if a platinum catalyst is also simultaneously evaporated it is observed that a platinum particle will naturally adhere to the surface of a carbon nanohorn. If this method is used, the complicated catalyst supporting process through the conventional wet process can be omitted resulting in a large cost reduction.

Until now, since the discovery of the carbon nanotube, although it has been acknowledged as having a high possibility of being applied to semiconductors, flat-panel displays, lightweight and high-strength raw material and fuel cells etc., it had stopped at the fundamental research as a material stage. This development however, is the first step for the practical utilization of carbon nanotube and big steps towards the development and expansion of nano-technology.

NEC, the Japan Science and Technology Corporation and the Institute of Research and Innovation will aim to practically apply the small fuel cell from here onwards and more proactively promote the research and development including production conditions of carbon nanotubes and the catalyst support on them.

Posted 30th August 2001

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