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TECHNOLOGY POLYMER
ELECTROLYTE Direct Methanol Fuel Cells Air-breathing Fuel Cell Stacks HIGH-TEMPERATURE ASSOCIATED |
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Polymer electrolyte-based direct methanol fuel cells (DMFCs) are a topic of extensive research at Los Alamos. They have been targeted by Defense Advanced Research Projects Agency (DARPA) as lightweight, portable power sources for soldiers in the field. Methanol is used because of its high power density, safety, low cost, ease of handling and distribution, and high electrochemical activity. Using a liquid fuel instead of a gaseous fuel also simplifies the system design. The Technology In a DMFC, methanol solutions in water are fed into the anode as fuel. This allows for a substantial system simplification relative to reformate-based fuel cells and a higher energy density than that presently available with hydrogen-based systems. However, at present DMFCs require much higher platinum loadings than either hydrogen or reformate-based systems. Background Since 1993 Los Alamos fuel cell researchers have been working to improve the performance of direct methanol fuel cells for automotive applications under the direction of the DOE Office of Enery Efficiency and Renewable Energy. In addition, substantial progress in developing DMFCs for battery replacement has been made under the auspices of DARPA since 1995. At the start of the project, research focused on improving anode performance, developing reliable diagnostics and screening membranes with reduced cross-over. Subsequently, the focus shifted to optimizing Nafion-based systems through various operational scenarios. Incremental improvements were made in membrane/electrode assembly (MEA) performance. These MEAs were incorporated into stacks for 80 W systems. Current research has several thrusts, all focused toward the development of stacks, yet including more aggressive attempts to identify and implement game-changing new components. Accomplishments Recent accomplishments include the development of improved membranes with lower cross-over, the successful deployment of MEAs based on these new polymers in fuel cells, the demonstration of stacks and (with Ball Aerospace) systems based on LANL stacks, the development of methanol sensors for use in systems and the development of lightweight high-performance stack hardware. Electrocatalytic advances have improved overall cell performance and efficiency. Some steps toward reducing catalyst loadings, thereby lowering cost, have also been taken. Research Objectives Research Approach (1) Develop advanced polymer electrolyte membranes with low methanol permeability (or cross-over from anode to cathode) and high protonic conductivity. Collaboration with Virginia Tech has led to promising new materials. Extensive work on understanding influence of polymer composition and morphology on transport parameters. (2) Improved anode activity through improved electrocatalysts and electrode structure. Work with several manufacturers is leading to advancements in catalysts. To advance the development of catalysts, we are implementing various approaches to catalyst nanoparticle production in-house. (3) Improved cathode performance with less catalyst involves work on new catalysts and electrode structures. (4) Improved MEA durability includes extensive diagnostic studies of electrode performance over time, identification of longevity limiting factors, and high throughput testing of new catalyst layer compositions. (5) Improved methods for rapid production of MEAs on lab scale are being developed. Point of Contact fuelcells@lanl.gov |
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