Enhancing direct solar thermochemical performance of modified CaCO3 with thermal transport networks composed of tetrapod-shaped ZnO whiskers

Abstract

The CaCO 3 /CaO based thermochemical system has great potential in Concentrating Solar Power (CSP) plants. However, the CaCO 3 suffers from high sintering speed, poor thermal conductivity, and weak light absorption, which is not conducive to being directly driven by solar energy. Herein, The Mn and Cr elements were doped into CaCO 3 through the sol-gel method. The synergistic effect between the two elements can maintain the storage density at 1057.3 kJ/kg after 20 cycles at 800 °C. The light absorption under AM 1.5G spectrum was obviously improved to 64.5% and reached 73.3% after 20 cycles. To further improve the thermal conductivity of the composite, the tetrapod-shaped zinc oxide whiskers (TZnO) were directly mixed into the composite. The TZnO acts as the thermal conductance bridge in the composites and can retain its original morphology at high temperatures without reacting with CaCO 3 . When 5% mole ratio of TZnO was added to the Cr/Mn doped CaCO 3 , the thermal conductivity increased by 17.8%. Through the non-isothermal analysis of the reaction kinetics, it is found that the addition of TZnO can effectively accelerate the reaction, especially at a higher heating rate, which is very beneficial to direct solar-driven applications. The optimized composites showed excellent properties in light absorption, sintering resistance, thermal conductivity, and reaction kinetics, which can guide the direct photothermal utilization of CaCO 3 . • Thermophysical properties of solar driven CaCO 3 -based composites are studied. • Tetrapod-shaped ZnO whiskers can serve as the thermal transport networks for CaCO 3. • The thermal conductivity increased by 17.8% after 5% mole ratio of TZnO was added. • The high thermal transfer network formed by TZnO accelerates the reaction kinetics.