Long-Term Thermal Cycling Test and Heat-Charging Kinetics of Fe-Substituted Mn2O3 for Next-Generation Concentrated Solar Power Using Thermochemical Energy Storage at High Temperatures

We studied the performance in terms of the long-term cyclic thermal storage and heat-charging kinetics of Fe-substituted manganese oxide for use in thermochemical energy storage at temperatures exceeding 550 °C in a next-generation concentrated solar power system in which a gas stream containing oxygen is used for reversible thermochemical processes. The Fe-substituted Mn2O3 was evaluated from the viewpoint of its microstructural characteristics, thermodynamic phase transitions, and long-term cycling stability. A kinetic analysis of the heat-charging mode was performed at different heating rates to formulate the kinetic equation and describe the reaction mechanism by determining the appropriate reaction model. Finally, the kinetics data for the sample obtained after the long-term cycling test were compared and evaluated with those of the as-prepared sample and kinetic literature data tested under different conditions. For the long-term cycled sample, the Avrami–Erofeev reaction model (An) with n = 2 describes the behavior of the first part of the charging mode, whereas the contracting area (R2) reaction model best fits the last half of the charging mode. For the as-prepared sample, except for the early stage of the charging mode (fractional conversion < 0.2), the contracting volume (R3) reaction model fits the charging mode over a fractional conversion range of 0.2–1.0 and the first-order (F1) reaction model fits in the fractional conversion range of 0.4–1.0. The predicted kinetic equations for both the samples were in good agreement with the experimental kinetic data.