| May 22, 2003 |
Toray Develops Direct Methanol Fuel Cells |
| Toray Industries, Inc. has been conducting research on the
development of direct methanol fuel cells (DMFCs) commissioned by the New Energy
and Industrial Technology Development Organization (NEDO). For the practical
application of DMFCs in the future, the company has already developed a novel
polymer electrolyte membrane capable of reducing methanol permeability through
membrane down to 20% relative to conventional membranes, and which can achieve
high power density and large energy capacity. Use of this electrolyte membrane
enables both the power density and the operating time (energy capacity) to be
tripled as compared with using conventional fluorine polymer-based electrolyte
membranes, even when the methanol concentration is 30%. As a ripple effect, the
membrane is expected to contribute to greater compactness and longer operating
time of devices such as cellular phones and other mobile electronic equipment. At present, there are two well-known types of fuel cells using polymer electrolyte membrane. One type is for automotive and residential applications, in which the fuel is hydrogen gas, and the other is DMFCs, in which methanol is used directly as the fuel. Because the latter type does not require a high-pressure hydrogen tank or large reforming equipment to generate hydrogen, it has the advantages of simplicity and compactness. In DMFCs, protons (hydrogen ions) generated on the fuel electrode side by a catalyst are conducted to the air electrode side through an electrolyte membrane, and are made to react with oxygen in the air to generate electricity. In this process, a phenomenon known as methanol cross-over (MCO) occurs, in which methanol permeates through the membrane with the protons. When MCO takes place, loss occurs due to methanol not being used to generate electricity, and the catalyst activity on the air electrode side decreases, leading to reduction of power density. At the same time, although it is desirable to increase the methanol concentration in order to use fuel in a vessel of limited size for as long as possible, this problem becomes more severe as the methanol concentration increases. With conventional fluorine polymer-based electrolyte membranes, it has been difficult to utilize methanol at high concentrations. Toray has since 2001 been undertaking DMFCs research commissioned by NEDO and in collaboration with Associate Prof. Yano of the Kyoto Institute of Technology, Associate Prof. Rikukawa of Sophia University, Prof. Takasu of Shinshu University, Prof. Taniguchi of Shinshu University and Prof. Sudo at Shizuoka University. The company has also conducted R&D concerning electrolyte membranes and catalysts, as well as Membrane Electrode Assembly (MEA) combining these components. With regard to polymer electrolyte membranes, directions for structure design of polymers at nano-level for suitable membrane were obtained on the basis of computer simulation data related to transportation of water and methanol in the membranes, as well as through fundamental research data carried out by each University and by Toray. Consequently, even when using non-fluorine polymers, it is possible to obtain electrolyte membranes that have greatly reduced MCO with virtually no decline in conductivity. Meanwhile, regarding electrode substrates, we studied the thickness and porosity of Torayfs carbon paper, which is the de facto standard for gas diffusion layer in polymer electrolyte fuel cells, and created a suitable configuration for use with DMFCs. For the catalyst layer, we have also created a configuration suitable for the newly developed electrolyte membrane by examining high-activity catalysts and improving the dispersion of catalysts. Through use of an MEA consisting of these membranes and electrodes, it has now become possible to achieve high power density and large energy capacity, even at high methanol concentration, and to obtain technical results that bring practical application much closer. With regard to the commercialization of electrolyte membranes and MEA, Toray is considering alliances with external corporations and research institutes with a view to developing their practical applications and possible commercialization by 2005. |
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