Toray Industries, Inc. announced that the company has succeeded in enhancing the capabilities of the membrane electrode assembly (MEA)2) and the polymer electrolyte membrane used in MEA, the primary element in a Direct Methanol Fuel Cell (DMFC)1), to a level where it could be put to practical use. The company for the first time in the world succeeded in developing a hydrocarbon-type membrane that suppresses methanol cross-over (MCO)3) to less than 1/10 of the existing fluorine-type membranes while maintaining the equivalent conductance. Furthermore, power generation capability of MEA was also greatly improved at high temperatures and high methanol concentrations, which are conditions that facilitate high power density.

Toray expects the newly developed technology to greatly contribute to the miniaturization as well as longer battery-life of mobile electronic devices such as notebook computers and cellular phones and plans to make a full-fledged business entry into the field. Moreover, the company also plans to work on the development of electrolyte membrane for automobiles based on this technology.

(Details of the technology)
With the conventional fluorine-type electrolyte membranes, the decline in performance due to the aforementioned MCO phenomenon made it difficult to put DMFC to practical use. Various types of low-MCO electrolyte membranes have been developed to tackle this issue but they resulted in a trade-off with weakened ionic conductance essential in power generation, failing to achieve practical use level. Therefore, the development of an electrolyte membrane that simultaneously achieves low-MCO and high ionic conductance was eagerly awaited.

Upon detailed analysis of the existing membranes, Toray found that the water inside polymers existed in form of a structure called clusters and it facilitated not only ionic conductance but also methanol permeation, thereby leading to the trade-off effect. Further, with a focus on the associated structure of polymer and water within the membrane and by combining the company’s core technology of polymer chemistry with nano-structure control technology, the company for the first time in the world succeeded in developing a membrane in which the water in the polymer contributes only to ionic conductance without increasing methanol permeation.

Moreover, Toray succeeded in significantly enhancing the power generation capabilities, durability and MCO compared with MEAs using existing fluorine-type membranes, by developing a revolutionary interface bonding method that remarkably increases the contact area between the electrode and the low-MCO electrolyte membrane.

The development announced this time includes the outcome of a project undertaken from the New Energy and Industrial Technology Development Organization (NEDO)4).

Key features of Toray’s technology
Direct Methanol Fuel Cell (DMFC)
(1) Electrolyte membrane
-Using its own design concept (a structure free of clusters), Toray succeeded in developing an innovative electrolyte membrane with ionic conductance of 1.0 and MCO value of 0.1 compared to existing membranes.

 (2) MEA
-Achievement of power generation capability and high durability through significant improvements in interface bonding capability between electrolyte membrane and electrodes.
 

Notes:
 1) Direct methanol fuel cell (DMFC)
DMFC is expected to become the next generation power source for mobile electronic devices. When compared with hydrogen-fueled Polymer Electrolyte Fuel Cells (PEFC), which are currently used in automobile and household applications, DMFC’s features are its potential in offering reductions in size and weight as well as improved portability.

2) Membrane electrode assembly (MEA)
MEA is the main component for power generation in fuel cells such as DMFCs and PEFCs. MEA consists of electrolyte membranes sandwiched between anodes and cathodes. Methanol solution, which is the fuel, reacts at the anode to produce protons (hydrogen ions). The protons permeate the electrolyte membrane and react with oxygen at the cathode, thus generating power.

3) Methanol cross-over (MCO)
Methanol cross-over is the phenomenon of permeation of methanol fuel through the electrolyte membranes of DFMC. Especially, the existing fluorine electrolyte membranes used in PEFC had the problem of methanol permeating along with proton (hydrogen ions) conducting. This methanol cross-over phenomenon leads not only to waste of fuel where methanol not used in power generation is lost due to methanol cross-over but also causes heat generation and lowering of power generation capability as the permeated methanol reacts at the cathode with oxidizes.
Efforts have been made to develop electrolyte membranes with reduced methanol cross-over but those typically led to a trade-off of lowered ionic conductance. Achieving low methanol cross-over rate and high ionic conductance has been a difficult issue. Compared with the existing fluorine electrolyte membrane, there was no publicly available information on an electrolyte membrane that could maintain an ionic conductance of 1.0 while lowering the MCO to less than 1/10.

4) NEDO (New Energy and Industrial Technology Development Organization)
Since 2001, Toray has been carrying out “Research and Development of High Efficient Direct Methanol Fuel Cells, Research and development of Polymer Electrolyte Fuel Cell Systems, Programme on Polymer Electrolyte Fuel Cells and Hydrogen Energy Utilization Technology,” a project undertaken from the Fuel Cell & Hydrogen Technology Development Department of NEDO. The technological content in this announcement is based on the outcome of the aforementioned program.