CaCo_0.05Mn_0.95O_3-δ: A Promising Perovskite Solid Solution for Solar Thermochemical Energy Storage

The redox cycle of doped CaMnO_3-δ has emerged as an attractive way for cost-effective thermochemical energy storage (TCES) at high temperatures in concentrating solar power. The role of dopants is mainly to improve the thermal stability of CaMnO_3-δ at high temperatures and the overall TCES density of the material. Herein, Co-doped CaMnO_3-δ (CaCo_xMn_1-xO_3-δ, x = 0-0.5) perovskites have been proposed as a promising candidate for TCES materials for the first time. The phase compositions, redox capacities, TCES densities, reaction rates, and redox chemistry of the samples have been explored via experimental analysis and theoretical calculations. The results demonstrate that CaCo_0.05Mn_0.95O_3-δ showed an enhanced redox capacity (1000 °C at pO₂ = 10^-5 bar) without decomposition and provided the highest TCES density of ∼571 kJ kg^-1 reported so far. The effective Co doping tended to increase the valence states of B-site cations in perovskite and facilitate the diffusion of the lattice oxygen atoms into the surface-active oxygen sites. Furthermore, the high cooling rates deteriorated the microstructure of CaCo_0.05Mn_0.95O_3-δ particles and resulted in incomplete heat release, which is instructive to the design and operation of the TCES systems.