Miniature fuel cells in a “flat-pack” configuration are being developed as alternatives to recharge- able batteries in cellular telephones, laptop computers, and other small, portable electronic devices. These fuel cells exploit the electrochemical oxidation of organic fuel (usually methanol) in air. Whereas power sources based on state-of-the-art lithium-ion batteries have specific energies of no more than ≈150 W⋅h/kg, power sources based on the present developmental fuel cells are expected to have specific energies between 500 and 1,000 W⋅h/kg. Moreover, whereas one must often wait for batteries to be recharged before using them, a fuel cell can be refueled and used immediately.
A flat-pack fuel-cell assembly can include one or more fuel cells electrically connected in series and/or parallel to obtain the required current and/or voltage rating. A typical basic flat-pack fuelcell assembly (see figure) contains a single polymer electrolyte membrane that serves multiple cells. The cathodes of all the cells are located side by side in the same plane on one side of the membrane, while the anodes of all the cells are similarly located on the other side of the membrane. A fuel-feed manifold and a wick deliver fuel in regulated amounts to the anodes. The cathodes are exposed to air in a manner similar to that of metal/air batteries.
Series electrical connections between adjacent cells are made in the form of posts that extend through the membrane. These posts are made from such corrosion-resistant, electronically conductive materials as graphite, platinum, and/or gold, along with (if needed) an appropriate stable polymeric binder. Alternatively or in addition, parallel and/or series electrical connections among cells can be made in the form of thin edge connector plates that include segmented strip conductors made of gold or graphite.
Fabrication of a multiple-cell membrane/ electrode assembly like that shown in the figure involves the application, to the membrane, of catalyst layers and backing structures for the anodes and cathodes. The techniques of fabrication include the use of catalyst inks and either the use of pre-coated electrodes or else sputter deposition of the electrodes. Gas-diffusion backing layers are preferably bonded to the membrane by hot pressing. Optionally, nonbonded backing layers can be used instead of bonded ones.
The preferred anode catalyst is Pt-Ru; the preferred cathode catalyst is Pt. The anode structure is made hydrophilic so that an aqueous solution of liquid organic fuel can readily flow to the catalyst layer and the carbon dioxide product can readily leave the anode surface. The cathode is made hydrophobic to exclude water and thereby facilitate the flow of air.
This work was done by S. R. Narayanan, T. I. Valdez, Filiberto Clara, and Frank Harvey of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Intellectual Assets Office JPL Mail Stop 202-233 4800 Oak Grove Drive Pasadena, CA 91109 (818) 354-2240 E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Refer to NPO-21066, volume and number of this NASA Tech Briefs issue, and the page number.
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Miniature Fuel Cells for Small, Portable Electronic Devices
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Overview
The document discusses the development of miniature fuel cells designed for small, portable electronic devices, such as cellular phones and laptops, by researchers at NASA's Jet Propulsion Laboratory (JPL). These fuel cells utilize a flat-pack configuration that significantly reduces bulk and complexity compared to conventional fuel cell assemblies, which typically include multiple components like bipolar plates, pumps, and blowers.
The innovative design features a polymer electrolyte membrane that serves multiple cells, with anodes and cathodes arranged side by side on either side of the membrane. This arrangement allows for efficient fuel delivery and air exposure, similar to metal/air batteries. The fuel cells primarily use methanol as the organic fuel, which undergoes electrochemical oxidation in the presence of air.
One of the key advantages of these developmental fuel cells is their expected specific energy, which ranges between 500 and 1,000 W⋅h/kg, significantly higher than the approximately 150 W⋅h/kg offered by state-of-the-art lithium-ion batteries. Additionally, fuel cells can be refueled and used immediately, eliminating the downtime associated with recharging batteries.
The fabrication process for these fuel cells involves applying catalyst layers and backing structures to the membrane, utilizing techniques such as catalyst inks and sputter deposition. The preferred catalysts are platinum-ruthenium for the anode and platinum for the cathode. The anode is designed to be hydrophilic to facilitate the flow of liquid organic fuel, while the cathode is hydrophobic to exclude water and promote air flow.
The document also emphasizes the potential for miniaturization and the ability to combine multiple basic subassemblies in a compact configuration to increase capacity. This advancement in fuel cell technology represents a significant step forward in providing efficient, portable power solutions for electronic devices, addressing the limitations of traditional battery systems.
Overall, the work highlights the collaboration between JPL and NASA, showcasing the innovative approaches being taken to enhance energy sources for modern technology. The document concludes with a notice regarding the rights for commercial use of the invention, indicating that inquiries should be directed to JPL's Intellectual Assets Office.
