Long-Term Stability of Doped Calcium Manganite for High-Temperature Thermal Energy Storage

Thermochemical energy storage (TCES) using oxygen carriers is gaining widespread attention for its potential to enhance the efficiency and scalability of concentrated solar power (CSP). This approach, which uses metal oxides undergoing redox reactions to store and release thermal energy, offers higher energy storage densities and operates at higher temperatures compared to conventional molten salts. However, the success of TCES depends on the development of oxygen carriers that can maintain stability over extended cycling at high temperatures. Perovskite oxides (ABO_3-δ) have emerged as strong candidates due to their excellent thermal stability and wide chemical flexibility. Calcium manganite (CaMnO_3-δ) is of particular interest due to its attractive storage capacity and earth-abundant constituent elements. Doping calcium manganite with elements such as strontium or yttrium on the A-site and titanium or iron on the B-site holds potential for enhancing redox performance and energy storage capacity. However, a detailed evaluation of their long-term stability after extensive redox cycling (1000+ cycles) is still needed. In this study, we investigate the key factors affecting the performance of these materials over prolonged use, including degradation mechanisms such as sintering, phase changes, and loss of reaction extent. Measurements of oxygen non-stoichiometry using thermogravimetric analysis (TGA) and tracking compositional changes through detailed characterization (XRD, SEM) are performed to understand how these materials evolve during cycling. Addressing these challenges is critical for the development of high-performance, durable TCES materials.