Al2O3/SiO2 co-doped calcium-based material derived from eggshell for thermochemical energy storage

Thermochemical energy storage can overcome the drawbacks such as instantaneity, instability, and the incongruity between supply- and demand-side in the utilization of renewable energy. CaCO3/CaO is regarded as a promising material for thermochemical energy storage, whereas its stability still requires urgent improvement. In this paper, a new Al2O3 and SiO2 co-doped calcium-based material derived from eggshell (ES) was prepared for efficient heat storage. The physicochemical properties of synthesized materials were systematically analyzed. The regulation mechanisms of Al2O3 and SiO2 additions on the cyclic characteristics of heat storage materials were investigated by a thermogravimetric analyzer. The results displayed that ESCa-2.5Si2.5Al, prepared with a mass ratio of ES: Al2O3: SiO2 = 95: 2.5: 2.5, demonstrated outstanding specific surface area of 14.64 m2/g and pore volume of 0.080 cm3/g, which were 2.74 and 5 times greater than those of ES-based CaO (ESCa), respectively. Meanwhile, SiO2 and Al2O3 could react with CaO to form Ca3Al2O6 and Ca2SiO4, their synergistic effect could efficiently improve the sintering resistance of CaO. Therefore, ESCa-2.5Si2.5Al possessed excellent cyclic stability. Its initial energy storage density was 2273.19 kJ/kg, and the retention ratio reached 72.93 % after 20 cycles, significantly higher than that of ESCa (19.35 %). In addition, compared with ESCa, the heat storage temperature of ESCa-2.5Si2.5Al decreased from 792 degrees C to 778 degrees C, and its carbonation rate only slightly attenuated over 20 cycles, enabling rapid heat storage at lower temperatures and stable heat release.