Enhancing cyclic durability in CaO-based thermochemical energy storage by Zr-Y co-doping: Mechanistic insights

The CaCO3/CaO materials are promising materials for thermochemical energy storage. However, they suffer from rapidly decreasing energy storage density over multiple calcination/carbonation cycles. This paper aims to select suitable inert supports with cyclic stability enhancement for the calcium looping (CaL) process at high carbonation reaction temperatures (> 800 degrees C). Firstly, four metallic elements (Zr, Mn, Y and Ce) were selected, and a single-doping strategy was used to screen out single-doping inert supports. By comparison, the 20Ca-Zr had the best energy storage performance, with an energy storage density (E-g,E-N=30) of 1744.72 kJ/kg after 30 cycles. Subsequently, the co-doping method was applied to further screen out co-doped combinations with long-term cyclic stability potential. The Zr was co-doped with Mn, Y and Ce, respectively. Among them, the 20Ca-0.5Zr-0.5Y displayed the best cyclic stability with an average energy storage density (E-g,E-av) of 1950.69 kJ/kg in 30 cycles. Based on the chosen Zr-Y co-doped CaO-based composite, the doping concentration optimization and multiple cycles tests were carried out. The effective conversion (X-eff) of 10Ca-0.5Zr-0.5Y decreased by only 4.9 % after 60 cycles. Therefore, the Zr-Y co-doped CaO-based composite, possessing robust sintering resistance effects, is promising for long-term TCES technology.