Extraction of CaFexMn1-xO3-δ Perovskite Reduction/Re-oxidation Thermodynamics via the CrossFit CEF Algorithm: A Thermochemical Energy Storage Application

Thermochemical energy storage (TCES) offers a pathway to store surplus electricity or heat as combined chemical plus thermal energy with high density, long-duration capability, and the ability to transport stored energy as stable solids. This study investigates an understudied material family for TCES by determining the temperature- and composition-dependent redox thermodynamics of CaFe _x Mn _1−x O _3−δ (CFM, 0 ≤ x ≤ 1) using the CrossFit Compound Energy Formalism (CF-CEF) algorithm. CF-CEF combines ab initio density functional theory (DFT) calculations with thermogravimetric (TGA) data to extract reduction and re-oxidation thermodynamics. We compare TCES capacities of CFM with those of CaAl _0.2 Mn _0.8 O _3−δ (CAM28), a benchmark material. The Fe-lean composition (x = 0.0625) achieves a thermochemical storage capacity of 53 kJ·mol⁻¹ O at a re-oxidation temperature of 760°C and a reduction temperature of 1250°C (ΔT = 490°C), excluding sensible heat, exceeding CAM28 by about 20%, and reaching a max of 60 kJ/mol at ΔT = 850°C. These findings identify Fe-lean CFM as a promising candidate for next-generation thermochemical energy storage.