Measuring Thermochemical Energy Storage Capacity with Redox Cycles of Doped-CaMnO3

Doped CaMnO3 perovskites can store energy thermochemically via reversible redox cycles with endothermic reduction at high temperature and intermediate oxygen partial pressures (PO2 ≈ 10-4 bar). Reoxidation in air and cooling to lower temperatures can release the stored energy. This study presents measurements of specific thermochemical energy storage in doped CaMnO3, notably CaCryMn1-yO3-δ and Ca1-xSrxMnO3-δ. Thermogravimetric measurements of equilibrium O non-stoichiometry (δ) at various temperatures and PO2 are fit to point-defect thermodynamic models to derive reaction enthalpy as a function of δ. Comparison of these models to calorimetry show specific thermochemical energy storage above 750 kJ/kg for cycles between 500 and 1000 °C with Ca0.95Sr0.05MnO3-δ having the highest specific energy. Kinetic experiments in a packed bed reactor give a measure of how rapidly energy can be incorporated into particles and provide a basis for developing future reactor models for energy storage or release in solar power plants and other applications.