Synergistic Enhancement of CaO-Based Thermochemical Energy Storage Performance via Mn–Co–Al Multidoping and Pyroligneous Acid Treatment

Calcium-looping-based thermochemical energy storage (TCES) technology can be embraced for peak load shifting in renewable energy generation systems. However, the energy storage properties of Ca-based materials rapidly decay after multiple cycles. In this study, a synergistic strategy involving pyroligneous acid impregnation and Mn–Co–Al incorporation was developed to improve the pore structure, enhance the oxygen vacancy concentration, and boost antisintering performance of the calcium-based composites, thereby significantly improving their TCES properties and cyclic durability. The modified CaO-based composites were systematically analyzed using various characterization methods to evaluate their heat storage performance, sintering resistance mechanism, and physicochemical properties. Characterization results revealed that the codoped sample with Ca:Mn:Co:Al = 100:12:4:5 (PACa-Mn12Co4Al5) possessed a loose and porous surface with a measured specific surface area of 13.72 m2/g, providing channels for CO2 diffusion into the inner particles. Ca3CoMnO6 and Ca3Al2O6, acting as inert supports, were uniformly distributed in PACa-Mn12Co4Al5, effectively mitigating sintering. The addition of Mn–Co–Al strengthened the basicity and promoted oxygen vacancy formation in PACa-Mn12Co4Al5. The oxygen vacancies encouraged the formation of ion diffusion channels, reducing the O2– transport resistance across the surface and within the bulk of PACa-Mn12Co4Al5, thereby improving the reaction activity and conversion efficiency. PACa-Mn12Co4Al5 demonstrated excellent heat storage performance under calcination at 750 °C and carbonation at 850 °C. After 40 and 100 cycles, its energy storage density remained at 97.29% and 84.65% of the initial value (1212.79 kJ/kg), respectively. Moreover, the average radiation absorptance of PACa-Mn12Co4Al5 reached 59.85%, 5.26 times that of limestone-based CaO. Therefore, PACa-Mn12Co4Al5 is a promising heat storage material, providing guidance for the industrial application of Ca-based TCES materials.