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August 20th, 2009

Microtubular SOFC: Small is beautiful – and cooler and powerful

Published on August 20th, 2009 | By: pwray@ceramics.org

A group from the National Institute of Advanced Industrial Science and Technology and the Fine Ceramics Research Association in Nagoya, Japan, reported in a recent issue of Science about their results in studying the anodedesign and electrochemical performance for SOFCs, including a tiny tubular SOFC that might be useful in small electronics.

They prepared three types of 1.9 mm diameter X 5 mm microtubular cells with NiO-Sc-stabilized zirconia (ScSZ) and Ce-doped zirconia (10Sc1CeSZ) for the anode, 10Sc1CeSZ for the electrolyte, and (La, Sr)(Fe, Co)O (LSCF)-Gd–doped ceria (GDC) for the cathode, with an interlayer of GDC betweenthe cathode and the electrolyte. The three kinds of cells were prepared. Each had different cosintering temperatures of the anode/electrolyte and thus different anode microstructures. The porositiesof the anodes were 54, 47, and 37% for the cells before reduction.

The first cell had Ni particles that were less than 100 nm in size. The size of Ni particles in the other two cell types was greater than 500 nm.

For the first cell (smallest Ni particle size), the researchers, using wet H, achieved maximum power densities of 1.1 and 0.5 W/cm2 at 600°C and 550°C, respectively, at a linear fuel velocity of 0.8 m/s.

In contrast, at 600°C, they found the maximum power densities of the other two to be 0.36 and 0.2 W/cm2, respectively.

One factor they looked at is fuel velocity. They noticed that in the first cell – the one with the greatest anode porosity – gas diffusion improved by when linear fuel velocity increased. They also note that the influence of linear fuel velocity becomes greater for lower operating temperatures.

Technology Review asked two ACerS members for their reactions to this study. Eric Wachsman, director of the Florida Institute for Sustainable Energy and chair of materials science and engineering at the University of Florida cautioned that the operating temperatures, even in microtubular SOFCs, may still be too high and that their long warm-up time limits their suitability for consumer electronics like cell phones. However, other AIST research asserts that in the micro ceramic parts, “the thermal shock resistance of the cell has been dramatically enhanced, thus enabling the fabrication of compact SOFC modules that can be used in rapid startup and shutdown operations.”

Harry Tuller, professor of ceramics and electronic materials at MIT, was pleased by the performance of the Japanese fuel cells but he has concerns that doping the electrodes and electrolytes with small amounts of rare and expensive materials, such as scandium.

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