Hydrogen Production via Chemical Looping Redox Cycles Using Atomic Layer Deposition-Synthesized Iron Oxide and Cobalt Ferrites

Abstract

Iron oxide (γ-Fe2O3) and cobalt ferrite (CoxFe3−xO4) thin films were synthesized via atomic layer deposition (ALD) on high surface-area (50 m2 g−1) m-ZrO2 supports. The oxide films were grown by sequentially depositing iron oxide and cobalt oxide, adjusting the number of iron oxide to cobalt oxide cycles to achieve a desired stoichiometry. High resolution transmission electron microscopy and X-ray diffraction indicate that the films are crystalline and have a thickness of ∼2.5 nm. Raman spectroscopy was used to confirm the predominance of the spinel phase in the case of cobalt ferrite. Films were chemically reduced at 600 °C using mixtures of H2, CO, and CO2. The evolution of oxide phases as a function of time during this reduction was observed using in situ X-ray diffraction, showing that γ-Fe2O3 are reduced only to FeO, while CoxFe3−xO4 are reduced all the way to a Co/Fe alloy. Subsequent water splitting measurements in a stagnation flow reactor yielded peak H2 rates exceeding virtually all of those rep...