| Summary: | In recent years, calcium-looping as one of the thermochemical energy storage technologies has attracted much attention. However, the poor cycling stability of conventional calcium-based materials limits the application of the calcium-looping. In this work, we prepare a novel calcium-based composite by Na2SO4-NaCl-ZnO co-doping. The properties of the composites are investigated by thermogravimetric analysis, X-ray photoelectron spectroscopy, in-situ X-ray diffraction, electron paramagnetic resonance, scanning electron microscope and Density Functional Theory calculations. The results indicate the Na2SO4 + NaCl-(CaO+0.5ZnO) composite is the most cost-effective material. After one cycle, the effective conversion of the composite is 89.8 %, which is 59.8 % higher than CaO. After 80 cycles, the effective conversion of composites decay 36.5 %. The enhancement mechanism is attributed to the formation of the high Taman temperature coordination compounds and oxygen vacancies generated by the coordination effect, and the rapid transport of oxygen ions derived from the oxo-Grotthuss effect. In addition, the averaged thermal energy density of Na2SO4 + NaCl-(CaO+0.5ZnO) is 2057 J/g after 80 cycles, which is a 43.9 % improvement compared to CaO. This work paves the way for the application of calcium-based thermochemical energy storage technology via achieving fast reaction rates and good cycling stability.
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