Thermochemical CO 2 splitting via redox cycling of ceria reticulated foam structures with dual-scale porosities

P Furler, J Scheffe, D Marxer, M Gorbar… - Physical Chemistry …, 2014 - pubs.rsc.org
P Furler, J Scheffe, D Marxer, M Gorbar, A Bonk, U Vogt, A Steinfeld
Physical Chemistry Chemical Physics, 2014pubs.rsc.org
Efficient heat transfer of concentrated solar energy and rapid chemical kinetics are desired
characteristics of solar thermochemical redox cycles for splitting CO2. We have fabricated
reticulated porous ceramic (foam-type) structures made of ceria with dual-scale porosity in
the millimeter and micrometer ranges. The larger void size range, with dmean= 2.5 mm and
porosity= 0.76–0.82, enables volumetric absorption of concentrated solar radiation for
efficient heat transfer to the reaction site during endothermic reduction, while the smaller …
Efficient heat transfer of concentrated solar energy and rapid chemical kinetics are desired characteristics of solar thermochemical redox cycles for splitting CO2. We have fabricated reticulated porous ceramic (foam-type) structures made of ceria with dual-scale porosity in the millimeter and micrometer ranges. The larger void size range, with dmean = 2.5 mm and porosity = 0.76–0.82, enables volumetric absorption of concentrated solar radiation for efficient heat transfer to the reaction site during endothermic reduction, while the smaller void size range within the struts, with dmean = 10 μm and strut porosity = 0–0.44, increases the specific surface area for enhanced reaction kinetics during exothermic oxidation with CO2. Characterization is performed via mercury intrusion porosimetry, scanning electron microscopy, and thermogravimetric analysis (TGA). Samples are thermally reduced at 1773 K and subsequently oxidized with CO2 at temperatures in the range 873–1273 K. On average, CO production rates are ten times higher for samples with 0.44 strut porosity than for samples with non-porous struts. The oxidation rate scales with specific surface area and the apparent activation energy ranges from 90 to 135.7 kJ mol−1. Twenty consecutive redox cycles exhibited stable CO production yield per cycle. Testing of the dual-scale RPC in a solar cavity-receiver exposed to high-flux thermal radiation (3.8 kW radiative power at 3015 suns) corroborated the superior performance observed in the TGA, yielding a shorter cycle time and a mean solar-to-fuel energy conversion efficiency of 1.72%.
The Royal Society of Chemistry
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