279062 Template-Directed Synthesis of Porous CoFe2O4/Al2O3 Reactive Structure with Atomic Layer Deposition for Solar Thermochemical Fuel Production

Tuesday, October 30, 2012
Hall B (Convention Center )
Darwin Arifin1, Victoria J. Aston2, Xinhua Liang2, Anthony H. McDaniel3 and Alan W. Weimer2, (1)Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, (2)Chemical and Biological Engineering, University of Colorado at Boulder, Boulder, CO, (3)Sandia National Laboratories, Livermore, CA

In this work, we examine a novel chemistry for a two-step, non-volatile metal oxide CO2 splitting cycle that utilizes the change in iron oxidation states (Fe2+/3+) between CoFe2O4 and FeAl2O4 spinel compounds within a novel nano-engineered reactive structure. The nano-engineered material was synthesized by template directed atomic layer deposition (ALD) of Al2O3, Fe2O3 and CoO. The structure maintained structural integrity over 10 heating cycles under conditions that mimic a concentrated solar power application, namely an oxidation temperature of 1000°C, reduction at 1460°C, and a heating rate of 16°C/s from low to high temperature.

The nano-engineered structure is ideal for solar thermochemical cycling due its highly porous nature that allows fast radiative heat transfer and high gas/solid reaction interface. Perhaps more important than the fast heat transfer is the ability to precisely control the thickness of the porous structure via ALD; this allows for the minimization of large excess Al2O3. A large excess of alumina would lead to diffusion of Co and Fe deeply into the bulk and undoubtedly have a detrimental impact on the redox kinetics. Oxygen uptake and release behavior of the nano-structure material is similar to that of ceria, which is well known to have high oxygen ion conductivity and rapid exchange kinetics. Raman spectroscopy was used to verify cycle chemistry.

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