Fuel Cells Bulletin 5 tend to break down at the temperatures (>800ยฐC) needed to prevent fouling of the catalytic surfaces by the formation of soot during reformation. The work is reported in the August issue of Advanced Functional Materials.
Fabrication begins with a polydimethylsiloxane mold placed on a flat surface to form an open-ended channel about 500 ยตm wide. A slurry containing polystyrene spheres 50 nm to 10 ยตm in diameter is then allowed to flow into the channel from one end by capillary action. Once the slurry reaches the far end, the polymer spheres begin to pack together as a result of solvent evaporation. When the packing process is complete, any remaining solvent is removed, leaving a sacrificial template consisting of a bed of closely packed spheres.
The spaces between the spheres are then filled with a low-viscosity, preceramic polymerbased liquid. After low-temperature curing, the mold is removed, leaving a stable, freestanding structure. Finally, the cured ceramic precursor is pyrolyzed in an inert atmosphere, decomposing the polystyrene spheres to leave an SiC or SiCN replica with a tailored structure of interconnected pores. The pore size can be tailored by the size of spheres used in the sacrificial template.
To demonstrate the material's potential as catalyst supports, samples were coated with ruthenium and incorporated within a stainless steel housing, where they successfully stripped hydrogen from ammonia at temperatures up to 500ยฐC. Kenis reports that in subsequent, unpublished work, the Ru-coated structure was incorporated in a ceramic housing, enabling successful decomposition of ammonia at temperatures up to 1000ยฐC. The ceramic structures themselves are stable to at least 1200ยฐC in air.
With improvements to the fabrication processes, Kenis believes support materials suitable for use in large-scale reformers could be created.
Kenis's team have also recently reported the development of a microfluidic, membrane-less fuel cell [FCB, May].