Mn/Fe co-doped CaO-based thermochemical energy storage materials

CaO-based materials are highly promising as energy storage candidates for next-generation concentrated solar power (CSP) plants, particularly those operating at temperatures exceeding 700 °C. However, the practical large-scale utilization of these materials is currently constrained by performance degradation over time and inadequate solar absorption capacity. Addressing these limitations is crucial for enhancing the viability and efficiency of CaO-based materials in CSP applications. In this work, we prepared a series of CaO-based energy storage materials doped with Mn, Fe, Mg, and Co using a simple and efficient co-precipitation followed by calcination method. Among these, the material co-doped with Mn and Fe exhibited the highest stability. At an elemental ratio of Ca12Mn1Fe2.4, the material maintains a high level of performance over the initial 60 cycles at 800 °C. Characterization results revealed that after calcination, a stable particulate material was formed, with the dopants uniformly dispersed throughout the matrix in the form of a brownmillerite phase, effectively preventing sintering at high temperatures. Moreover, Mn/Fe co-doping increased the solar absorptance by over fourfold compared to pure CaO. DFT simulations indicated that the Ca₂Mn_0.34Fe_1.66O₅ material with a brownmillerite structure exhibits a strong adsorption capability for calcium oxide clusters. This study not only demonstrates an effective approach to enhancing the thermal stability of CaO-based materials but also provides new insights into the development of high-performance thermal energy storage solutions.