Experimental investigation on the CaO/CaCO₃ thermochemical energy storage with SiO₂ doping

Thermochemical systems offer high energy densities and the possibility of long-term storage for the promotion of renewable energy utilization. In particular, CaO/CaCO₃ is a very promising system in the field of thermochemical energy storage due to its high energy density, widespread availability and low cost. However, this system makes stringent demands on the performance of CaO/CaCO₃ energy storage, including the high reactivity and robust cycling stability. In this study, thermodynamics, kinetics and cycling stability of SiO₂-doped CaCO₃ are investigated by thermogravimetric analysis and differential scanning calorimetry. The obtained results show that SiO₂ has a slightly negative effect on heat storage capacity, but the amount of released heat is increased, and the specific heat capacity is improved by 20% due to the high thermal conductivity of SiO₂. Additionally, samples with an optimal mass ratio of 5% SiO₂ show a decrease in the activation energy by approximately 40 kJ/mol because an increase in SiO₂ surface coverage (>10 wt.%) leads to a reduction in the calcination conversion. Moreover, the cycling stability of SiO₂-doped CaCO₃ is enhanced by 28% with an attenuation ratio of 0.85% per cycle, especially at 700 °C, which is ascribed to the faster CO₂ diffusion at higher carbonation temperature.