High performance Mn/Mg co-modified calcium-based material via EDTA chelating agent for effective solar energy storage

Calcium-based material is a very promising candidate energy storage material for next generation concentrated solar power (CSP) plants with operation temperatures above 700 °C. However, performance decay and poor solar absorption capacity limit the large utilization of calcium-based material. Here, ethylene diamine tetraacetic acid (EDTA)-assisted sol–gel method is first employed to modify CaO with magnesium (Mg) and manganese (Mn) elements. MgO and Ca2MnO4 nanoparticles are attached to the surface of CaO particles to separate grains spatially to inhibit sintering. In addition to the external separation effect, Mn elements are found to be doped successfully into CaO crystal lattice rather than simply mixed, which restrains atomic diffusion and agglomeration inside CaO and thus further inhibits sintering more efficiently. The Mg and Mn co-doped sample (Ca:Mn:Mg = 9:1:2) synthesized by EDTA demonstrates exceptional thermal stability at 800 °C. The performance decay is only 6.3 % after 100 cycles and mainly manifests in the first ten cycles (4 %). Furthermore, by combining two-step calcination to avoid agglomeration and uneven doping, we also obtain the co-doped sample (Ca:Mn:Mg = 9:1:1) with nearly no performance decay in 100 cycles. The proposed materials possess an average solar absorptance of 67 %, about 4 times that of pure calcium material. This work not only designs energy storage materials with excellent performance expected to be applied in the next generation CSP plant but also provides a lattice doping route for calcium-based material modification.