Dark calcium carbonate particles for simultaneous full-spectrum solar thermal conversion and large-capacity thermochemical energy storage

Possessing nontoxicity, high thermochemical energy storage density, and good compatibility with supercritical CO₂ thermodynamic cycles, calcium carbonate (CaCO₃) is a very promising candidate in storing energy for next-generation solar thermal power plants featured with high temperature over 700 °C. However, CaCO₃ particles are usually white with little absorption of sun light, inhibiting their application in efficient volumetric solar energy conversion systems. In this paper, dark CaCO₃ particles are designed by doping with Cu, Fe, Co, and Cr elements based on sol-gel procedures. For particles doped with only Cu elements, the solar absorptance in the visible range is improved prominently while that in the near-infrared does not change so much. By further adding Cr elements, full-spectrum absorption of solar energy is achieved with a value as high as 73.1%, but the energy storage density decreases rapidly with cycling. By incorporating Mn or Al elements, the cyclic stability is enhanced greatly. For binary-doped particles with Cu and Mn, the energy storage density achieving 1952 kJ kg⁻¹ after 20 cycles, which is 84% higher than that of pure CaCO₃ particles. Additionally, the average solar absorptance is still considerable with a value of ~60% after 20 cycles. This work guides the design of high-efficiency, large-capacity, and stable thermochemical energy storage particles for simultaneous solar thermal conversion and high-temperature thermochemical energy storage.