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 degrees 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 similar to 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.