Cobalt Ferrite in YSZ for Use as Reactive Material in Solar Thermochemical Water and Carbon Dioxide Splitting, Part II: Kinetic Modeling

Abstract

The kinetics of 10 wt.% cobalt ferrite (CoFe2O4) in 8 mol.% yttria-stabilized zirconia, synthesized via the co-precipitation method and formed into a porous structure, are investigated in support of simulating the performance of a solar thermochemical reactor. Kinetic parameters for the thermal reduction (T-R) of CoFe2O4 at temperatures of 1325–1500°C were investigated by thermogravimetry. A nonlinear best fit of a uniform conversion model was used to determine kinetic parameters from experimental data. In the temperature range of 1375–1450°C, the activation energy and preexponential term were found to be 386 ± 13 kJ mol−1 and 8.8 × 109 ± 2.0 × 108 min−1, respectively, while increasing at higher temperatures. Simultaneous thermogravimetric analysis and differential scanning calorimetry studies showed an increase in the reaction rate of T-R upon the onset of melting (1440°C). Oxidation studies of the material using CO2 yield an activation energy and preexponential term of 52.1 ± 6.8 kJ mol−1 and 2.86 ± 0.2 min−1, respectively, which is in good agreement with past work. The reaction order for CO2 was determined to be 0.750 ± 0.08. The reaction kinetics for oxidation using CO2 were best described by a 3-D diffusion Jander model.