Jonathan R. Scheffe1, Nathan P. Siegel2, Mark D. Allendorf2, and Alan W. Weimer1. (1) Department of Chemical and Biological Engineering, University of Colorado, 1111 Engineering Dr., ECCH 111, Boulder, CO 80309-0424, (2) Solar Technologies, Sandia National Laboratories, PO Box 5800, Albuquerque, NM 87185
Nano-thick cobalt-iron spinel oxides (cobalt ferrites) have been synthesized via atomic layer deposition (ALD) on nano-scale yttria-stabilized zirconia (YSZ) and Al2O3 supports. ALD has the advantage of being able to precisely control the thickness and Co/Fe ratio on the atomic level, which is significant because it has been suggested that this two-step cycle is a surface dominated reaction. The kinetics of the water splitting step has been investigated and results indicate that the temperature required is decreased due to a reduction of diffusion limitations. Additionally, results were directly compared to samples synthesized via traditional methods (coprecipitation, etc), and the amount of hydrogen generated per mole of ferrite was shown to be greater. Potential factors affecting the water splitting step that were studied included film thickness, Co/Fe ratio, and the substrate material (YSZ and Al2O3), and each was shown to be statistically significant. Hydrogen evolution was measured in situ using a residual gas analyzer, and changes in crystallinity were measured using a powder x-ray diffractometer.