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. CaCO 3 /CaO is regarded as a promising material for thermochemical energy storage, whereas its stability still requires urgent improvement. In this paper, a new Al 2 O 3 and SiO 2 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 Al 2 O 3 and SiO 2 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: Al 2 O 3 : SiO 2  = 95: 2.5: 2.5, demonstrated outstanding specific surface area of 14.64 m 2 /g and pore volume of 0.080 cm 3 /g, which were 2.74 and 5 times greater than those of ES-based CaO (ESCa), respectively. Meanwhile, SiO 2 and Al 2 O 3 could react with CaO to form Ca 3 Al 2 O 6 and Ca 2 SiO 4 , 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 °C to 778 °C, and its carbonation rate only slightly attenuated over 20 cycles, enabling rapid heat storage at lower temperatures and stable heat release.