Existing methane fuel cells typically require high (750–800°C) temperatures to activate methane in a separate methane reformer that creates hydrogen gas. Now researchers at the Georgia Institute of Technology (Georgia Tech; Atlanta; www.gatech.edu) have developed a solid oxide fuel cell (SOFC) design that eliminates the need for a methane reformer and requires temperatures of only 500°C. The cost savings enabled by the lower-temperature operation could make this type of fuel cell, which uses no platinum, commercially viable for several applications, including distributed power generation and automobile engines.
“In our fuel cell, we integrated thermal catalysis and electrocatalysis at 500°C,” explains Meilin Liu, Georgia Tech professor and lead researcher. “Methane is first reformed to CO and H2 within the fuel cell, and then the H2 and CO are electrochemically oxidized to H2O and CO2 on the electrode.”
The lower-temperature fuel cell would allow ordinary stainless steel, rather than exotic materials, to be used for the interconnectors that link the cells into a stack. “Above 750°C, no metal can withstand the temperature without oxidation,” Liu says, so the materials needed are “expensive and fragile, and would contaminate the active components of the cell.”
To eliminate the need for steam reforming, the fuel cell features a new catalyst developed for this project by University of Kansas (Lawrence; www.ku.edu) researchers. The catalyst contains nickel and ruthenium active sites anchored on cerium oxide, and aids the chemical cleavage of methane and water, the products of which recombine as H2 and CO. The catalyst material is applied as a coating on the anode of the fuel cell (diagram).
As electrical current flows, the CO and H2 are oxidized to CO2 (in amounts lower than in a combustion engine) and water, which is cycled back into the fuel cell to combine with the methane.
Liu and colleagues have also developed a specialized cathode that accelerates the reduction of oxygen and its movement through the system by using nanofiber cathodes —work which the group previously published. The nanofiber cathode has high surface area, high porosity and lower tortuousity, Liu says, providing more efficient paths for mass and electron transfer.
The researchers are working on stacking the fuel cell into a prototype power device.
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