Impregnated layer solution combustion synthesis of dark Ca-based thermochemical energy storage composites for direct solar-driven calcium looping

Abstract

Ca-based thermochemical energy storage (TCES) materials hold promising prospects for thermal energy storage, considering their energy storage density, temperature compatibility, material safety, and cost. Nevertheless, challenges such as the susceptibility to sintering, and limited light absorption capabilities inherent in Ca-based TCES materials markedly restrict the practical deployment of solar-driven calcium looping (CaL) technology. Hence, this study employs impregnated layer solution combustion synthesis method fabricating Fe/Mn-doped Ca-based materials for thermochemical heat storage. Research indicates that 750 ℃ is the ideal temperature for combustion synthesis. Exceeding this temperature can lead to excessive sintering of Ca-based materials, while falling short results in the in-situ formation of the CaCO₃ phase, both of which can degrade the pore structure of Ca-based TCES composites. The properties of synthesized materials are influenced by the type of impregnated layer template to some extent, with degreasing cotton yielding the Ca-based TCES composites with the most superior thermochemical heat storage properties. In addition, the Fe/Mn-doped Ca-based composite (Ca:Mn:Fe = 100:2:4) demonstrates excellent heat storage property (average energy storage density of 1.32 MJ/kg and an energy density loss of only 4.4 % during 20 cycles), along with favorable light absorption characteristics (solar absorption rate of 63.9 %). This is mainly due to the rich pore structure inherited from the degreasing cotton, and the Fe and Mn elements deepened the surface color of the synthetic material, and acted as an inert skeleton to alleviate the high-temperature sintering of the Ca-based TCES composites to a certain extent.