NEWS OF THE WEEK ELECTROCHEMISTRY
FUEL CELLS MINUS MEMBRANES Laminar flow in microfluidic channel prevents fuel and oxidizer from mixing
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KEY COMPONENT OF
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mon fuel cells—the membrane that isolates the fuel from the oxidizer—has been eliminated in a new fuel-cell design that uses microfluidic effects to separate the reagents. The design simplifies the electrochemical devices and may lead to new types of fuel cells that are free from the problems that typically bedevil membrane-based power systems. The membrane that is found in polymer electrolyte membrane (PEM) fuel cells serves as a barrier to prevent the fuel and oxidizer from mixing without generating electricity. Ideally, electrons and protons from a fuel are liberated at a catalystcoated anode and travel via separate routes to a cathode where they react with an oxidizer. Protons migrate through an electrolyte m e d i u m — t h e membrane—while electrons travel through an external circuit to provide electrical power. Much of the research on PEM cells focuses on improving the membrane to improve overall cell performance. For example, scientists are trying to find robust substitutes for the commonly used membranes that can tolerate temperatures higher than about 80 °C, the temperature at which PEM cells are typically operated. Raising the temperature would speed up reaction kinetics but may dehydrate the membrane, which would reduce proton conduction and cell performance. Fuel permeating through the membrane is another problem. Now, researchers at the UniHTTP://WWW.CEN-ONLINE.ORG
versity of Illinois, Urbana-Champaign, have sidestepped these issues by devising a fuel cell that omits the membrane. By pumping aqueous fuel and oxidizer solutions through a micrometersized Yshaped channel, the group induces laminarflowin which the reagents proceed along the length of the channel in parallel streams with no mixing except for a small amount of diffusion that's controlled by the channel dimensions and flow rates {J. Power Sources, 128,54 (2004)}. T h e team, which includes graduate student Eric R. Choban, assistant chemical engineering professor Paul J. A. Kenis, and their coworkers, uses standard techniques to prepare the channels in polymeric materials. And they use electrodeposition methods to form platinum-black
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electrodes along the length of the channel on opposite walls. Kenis points out that, unlike related work by other research groups in which inorganic compounds react in a redox cell to generate electrical current, the microfluidic system uses readily available reagents including methanol, formic acid, potassium permanGO WITH THE FLOWlna ganate, and oxygen. membraneless microfluidic In the prototype fuel cell, laminar flow of fuel fuel cell's current form, and oxidizer solutions fuel efficiency is low, through a Y-shaped channel Kenis acknowledges. of micrometer-scale width One approach to imprevents the reagents from proving performance mixing without generating is to include additionelectricity. As shown, oxidizer al channel outlets to and fuel diffuse slightly in remove small amounts opposite directions. Blue of depleted reagents, regions are areas where the thus allowing unused reagents have been depleted. solutions to reach the electrodes. The group also is experimenting with a design in which a recirculating electrolyte stream flows between the fuel and oxidizer and is "spiked" regularly with small amounts of fresh fueL-MITCH JACOBY
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Implant Settlement Free To Proceed
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ow Corning could emerge from bankruptcy reorganization later this year, and silicone gel breast implant recipients could be seeing some money in 2005. Attorney Geoffrey White—whose firm, White, Meany & Weatherall, represents 48 Nevada women—says he is dropping his appeal of Dow Coming's $3.2 billion settlement with implant recipients. "It simply became clear that the process would take too long for very sick women in Nevada and elsewhere to recover for their injuries," White said in a news release. It has been 12 years since FDA banned most sales of silicone gel breast implants and nine years since Dow Corning filed for bankruptcy reorganization. However, a number of objections, from
foreign claimants and a U.S. government claim now settled, also prevented a final resolution. White's appeal "was really the last major obstacle to the settlement," a Dow Corning spokeswoman says. Dow Corning was at one time the largest implant maker and supplied silicone gel to other implant providers. Three of those providers—Baxter Healthcare, 3M, and Bristol-Myers Squibb—along with gel supplier Union Carbide, agreed to a separate settlement in 1995 worth about $2.5 billion. "Is this settlement long overdue or what?" asks Lynda Roth, president of the Coalition of Silicone Survivors, a support group for women. "Finally, the sickest women won't have to wait much longer to get some money."-MARC REISCH
C & E N / MARCH 29, 2004
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