A new high performance, low cost heterogeneous composite bipolar plate has been developed. Unlike the well publicized carbon composite bipolar plate, in which graphite powder and plastics are mixed thoroughly, the new plate has its “ribs” made of flexible and loose carbon fiber bunches while the rest of the plate is plain plastic. This design has brought many advantages: low contact resistance acquired under very low compression force, less stack weight and volume, full electrode utilization, and thus high performance and low cost. It also eliminates the need for supplementary devices for fuel circulation among cells in a stack and makes DMFC portable.

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Novel designs of a cylindrical and a flat portable direct methanol fuel cell (DMFC) have been proposed in this research. Experimental cells have also been fabricated. Their maximum power output reached 12mW∕cm2 when operating at room temperature and with naturally breathed air. The weight and the volume of the experimental cylindrical cell are 27g and 30cm3, respectively, with 7.5cm3 of methanol inside. Its specific power and volumetric power density are 6.67mW∕g and 6.25mW∕cm3, respectively. The membrane electrode assembly was fabricated by hot pressing the electrodes purchased from E-Tek Co. The catalyst contents are 4.0mg∕cm2 of Pt∕Ru (80wt.% carbon supported) and 4.0mg∕cm2 of Pt (black) for anode and cathode, respectively. The new and compact design will make the portable DMFC lighter and cheaper, and bring it one step closer to be marketable.

A new hydrophobic micropillared structure for the electrode of a proton exchange membrane fuel cell (PEMFC) is proposed in this study. Its performance has a 40% increase over the conventional structured electrode. The new design changes the gas-diffusion layer (also called microporous layer (MPL)) of the cathode of a PEMFC to a gas-abundant-layer (GAL) by mixing a high percentage of polytetrafluoroethylene (PTFE) into the carbon powder. Unlike the generally flat MPL, the surface of the GAL in contact with the catalyst layer has tens of thousands of micropillars on top of it so that its area can be increased significantly. The interfacial region between the GAL and the catalyst layer will become the main reaction sites because the heavily PTFE treated GAL will be filled with oxygen passageways while most of the catalyst layer of the cathode will eventually be filled with the water produced in the operation. The experimental results with different pillar sizes have shown that the area of the interfacial surface between the GAL and the catalyst layer is the key factor in determining the cell performance and should be made as large as possible.

There are several problems associated with the marketing of portable direct methanol fuel cell (DMFC). The most critical one is how to supply fuel to all cells without supplementary devices. It requires a serial connection of 12, 24 and 48 cells to acquire enough voltage to operate a cellular phone, a digital video camera and a personal computer, respectively. How can methanol be supplied to all these cells if the conventional stacking method is adopted? Supplementary devices such as pumps, fans, and complex piping system must be used and, as a result, the word “portable” no longer applies. New stacking approach must be developed before portable DMFC can be put onto the market. The idea behind the promising “banded” type stack is simple. Problems only come when one tries to implement it. What is the actual device that can collect and transport those electrons between electrodes with minimum electrical resistance and, yet, be able to survive in the acidic environment inside the cell and, more importantly, not to harm the membrane electrode assembly (MEA)? Currently, there is none with reasonable cost. The new heterogeneous composite bipolar plate developed in our laboratory is composed of rows of carbon fiber bunches and plastic main plate body. The carbon fiber bunches are perpendicular to and penetrate through the main plate body. Besides being light, better performance, and low cost, the new plate has a unique property. Since the main plate is an insulator, the rows of fiber bunches may be arranged to be electrically independent with each other. When MEA is made into banded structure and with each band corresponding to one row of fiber bunch on the plate, all bands will function as different cells and higher voltage may be acquired in a smaller volume. Thus, just two bipolar plates (“unipolar” should be called in this case) with one “banded” MEA in between can form a very simple multi-cell stack. The serial connection may be done outside the cell and, therefore, low cost metal such as copper, which has great electrical conductibility but is harmful to MEA, may be used to transport the electrons which are conveyed outside the cell through carbon fiber bunches in the first place. The fact that it has only one anode chamber and one cathode chamber eliminates the difficult problem of distributing fuel sufficiently to all cells without supplementary devices. As a matter of fact, the anode chamber may be used as a methanol storage tank to further reduce the volume. The structure of the new stack design presented in this paper is simple, durable and low cost. It holds the key to the success in marketing the portable DMFC.