(504d) Oxidation Kinetics of Hercynite Alloys for Solar Thermochemical Fuel Production
In this work, we evaluate four spinel aluminate materials with varying cobalt contents from 0 to 40% (FeAl2O4, Co0.05Fe0.95Al2O4, Co0.25Fe0.75Al2O4, and Co0.40Fe0.60Al2O4) in order to further understand the role of cobalt in these materials and to quantify its effect on the thermodynamic and kinetic properties for CO2 reduction. A solid state kinetic analysis was performed on each sample to model its oxidation kinetics in CO2 splitting experiments at temperatures ranging from 1200°C to 1350°C using a thermogravimetric analyzer (TGA). An F1 model representing first-order reaction kinetics was found to most accurately represent the experimental data for all materials evaluated. The computed rate constants, activation energies, and pre-exponential factors all increase with increasing cobalt content. However, lower productivities are seen with increasing cobalt content. High temperature in-situ XPS study was utilized, for the first time on these oxides, to characterize their surfaces and indicated the presence of metallic states of the reduced cobalt-iron alloys, which are not present in hercynite. These species provide a new site for the CO2 reduction reaction and enhance its rate through an increased pre-exponential factor.