SUMMARY

The thermal reduction of reduction/oxidation (redox)-active mixed ionic electronic conducting (MIEC) materials will be examined under vacuum for a range of temperature. MIEC materials with the perovskites are particular interest due to rapid kinetics, thermal stability and tunability via cation substitution. The rapid kinetics are due to facile conduction of oxygen ions and electrons that participate in the reaction. These redox-active MIEC materials can be directly integrated into a two-step solar thermochemical cycle via reversible reactions to store solar irradiation via sensible and chemical means. The two steps of the cycle encompass 1) the endothermic thermal reduction at high temperatures and low O2 partial pressures driven by concentrated solar irradiation to produce oxygen vacancies in the sublattice and 2) the oxidation at high O2 partial pressures in an exothermic reaction to release the heat in a non-solar step. In this work, the thermal reduction of redox-active MIECs was examined by coupling a high-flux solar simulator (HFSS) to an upward flow reactor (UFR). The oxygen produced by reduction was measured using mass spectroscopy coupled with gas chromatography. The focus of this work is to examine the rate limiting mechanisms through measurements with the UFR coupled to robust heat and mass transfer modeling.