LAUSR

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.