Rapid and stable calcium-looping solar thermochemical energy storage via co-doping binary sulfate and Al–Mn–Fe oxides

Solar thermochemical energy storage based on calcium looping (CaL) process is a promising technology for next-generation concentrated solar power (CSP) systems. However, conventional calcium carbonate (CaCO3) pellets suffer from slow reaction kinetics, poor stability, and low solar absorptance. Here, we successfully realized high power density and highly stable solar thermochemical energy storage/release by synergistically accelerating energy storage/release via binary sulfate and promoting cycle stability, mechanical strength, and solar absorptance via Al–Mn–Fe oxides. The energy storage density of proposed CaCO3 pellets is still as high as 1455 kJ kg−1 with only a slight decay rate of 4.91% over 100 cycles, which is higher than that of state-of-the-art pellets in the literature, in stark contrast to 69.9% of pure CaCO3 pellets over 35 cycles. Compared with pure CaCO3, the energy storage power density or decomposition rate is improved by 120% due to lower activation energy and promotion of Ca2+ diffusion by binary sulfate. The energy release or carbonation rate rises by 10% because of high O2− transport ability of molten binary sulfate. Benefiting from fast energy storage/release rate and high solar absorptance, thermochemical energy storage efficiency is enhanced by more than 50% under direct solar irradiation. This work paves the way for application of direct solar thermochemical energy storage techniques via achieving fast energy storage/release rate, high energy density, good cyclic stability, and high solar absorptance simultaneously.