(388s) Template-Directed Synthesis of Porous CoFe2O4/Al2O3 Reactive Structure with Atomic Layer Deposition for Solar Thermochemical Fuel Production

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 (Fe^2+/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.