Decorating Calcium-Based Materials with Transition Metal Elements for Directly Capturing and Storing Solar Energy

Direct solar-driven thermochemical energy storage system puts forward new requirements for calcium-based materials with high optical absorption, high capacity of energy storage density, high cycling stability, and low costs. In this work, the novelty relies on the fact that calcium-based composites modified by transition metal elements can directly capture solar energy for storing. Meanwhile, this work provides the design criteria of calcium-based materials with high optical absorption in theory and screens appropriate decorating elements to modify CaCO₃ for satisfying multiple demands in experiments. The design criteria for promoting light absorption of calcium-based materials were established by electromagnetic theory while the dark transition metal elements (Cr, Mn, Fe, Co, Ni, and Cu) were doped in binary combination to experimentally modify calcium-based composites through the sol-gel method. The results indicate that calcium-based materials with porous structure (doped with Mn element) not only have high optical absorption (>75%) but also possess high cycling stability (attenuation <9% after 20 cycles) and high capacity of energy storage density (>1260 kJ/kg). After comprehensive consideration of optical absorption, cycling stability, capacity of energy storage density, and economic cost, the samples of Ca-Mn-Fe = 100-2-4 and Ca-Cr-Mn = 100-2-4 stand out to be the most promising candidates for large-scale application of thermochemical energy storage. This work provides novel promising calcium-based materials for direct solar-driven thermochemical energy storage system to realize high-efficiency solar thermal conversion.