Evaluation of Thermochemical Energy Storage Performance of Fe-/Mn-Doped, Zr-Stabilized, CaO-Based Composites under Different Thermal Energy Storage Modes

CaCO3/CaO materials possess the advantages of low cost, high energy storage density, and working temperature, which offer these materials the potential to be used in thermochemical energy storage systems for concentrated solar power plants. However, CaCO3/CaO materials possess poor antisintering and optical absorption abilities, largely limiting their practicability for direct solar utilization. In this study, binary ion doping of Fe/Mn and Zr-based stabilizer incorporation were simultaneously conducted to improve the cyclic thermal energy storage/release performance of CaCO3/CaO materials. The spectral absorbance of synthetic CaO-based composites (ranging from 77.8% to 84.0%) doped with binary ions of Fe/Mn is greatly increased in comparison to that of pure CaO (∼12.2%) due to the generation of black Ca2Fe2O5 and Ca4Mn3O10. The cyclic thermal energy storage/release performances of synthetic CaO-based composites were comparatively investigated under two thermal energy storage modes (CSP-N2 and CSP-CO2). The Zr-doped, CaO-based composites exhibit a cycling stability superior to those of Zr-free CaO-based composites due to the generated inert CaZrO3 with desirable antisintering ability, and the superiority is more prominent under CSP-CO2 mode. After 50 cycles, the CaO-based composite with a molar ratio of Ca:Zr = 100:6.7 exhibits a remarkably stable energy release density of 1.02 MJ/kg under CSP-CO2 mode, retaining 88.9% of its initial energy release density.