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October 6th, 2009

Lowering the temperature of SOFCs

Published on October 6th, 2009 | By: pwray@ceramics.org

This scanning-electron-microscope image shows the microstructure of a solid oxide fuel cell. A section of the anode, which is made of a new material, is visible at right. At left, part of the cathode is visible. The smooth area in the middle is the electrolyte.

Technology Review reported that researchers at Georgia Tech have developed an anode material that resists the buildup of sulfur and carbon that can occur at lower temperatures. SOFCs require high temperatures to run efficiently. The higher the temperatures, the higher the costs.

Nickel, often used as a catalyst in the anode, is prone to contamination by sulfur in the fuel, and it can get covered in carbon residue, particularly at low temperatures. Both of these factors tend to clog the cell and reduce performance.

The new anode material, described in the journal Science, resists sulfur poisoning and carbon coking, even when running at low temperatures, and without compromising performance. Developed by researchers led by Meilin Liu, professor of materials science and engineering and codirector of the Center for Innovative Fuel Cell and Battery Technologies at Georgia Tech, the material has so far been tested over a period of 1,000 hours at temperatures ranging from 500°C to 700°C.

“If you can run at lower temperatures, you have a greater choice of structural materials to work with,” says J. Robert Selman, professor of chemical engineering at Illinois Institute of Technology.

The new anode material is a composite of nickel and a ceramic that contains small amounts of two rare-earth metals. Other groups have developed sulfur- and coking-tolerant anodes, but these incorporated expensive materials and degraded cell performance. Replacing the nickel with copper improves a fuel cell’s tolerance, but copper isn’t as good a catalyst. Coating a conventional anode with ruthenium also prevents sulfur and carbon deposition, but this metal is extremely expensive. And all previously developed anodes, no matter how resistant to coking and poisoning, suffered a performance drop when switched to dirty fuels, says Liu. The Georgia Tech anode, he says, “gives the best performance.”


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