Hydration reactivity enhancement of calcium oxide-based media for thermochemical energy storage

The calcium oxide/water/calcium hydroxide system is a promising material system for thermochemical energy storage (TCES). Its high reactivity under various experimental conditions during the cyclic operation of heat storage-and-release is a key challenge for practical applications. In this study, we developed a new type of highly durable TCES medium with hydration reactivity enhancement. The composite materials were prepared by heat treatment of a mixture of calcium carbonate and additives, consisting of tetraethoxysilane (TEOS) and a silane coupling agent, bis(3-triehoxysilylpropyl) pertetrasulfide (SCA). The kinetic performances of the composites and CaO were compared. It was observed that the additives promoted hydration reactivity at 450 degrees C and 70kPa, and 0.6 wt% composite exhibited the highest thermal output. Furthermore, it was found that the enhancement in hydration reactivity was affected by the experimental conditions as significant enhancements were observed when the experimental conditions were closer to equilibrium, while almost no enhancement was observed when the conditions were far from equilibrium or at a high vapor partial pressure. Sample characterization via X-ray diffractometry and scanning electron microscopy revealed that the agglomeration of CaO particle grains was alleviated by pinning effects, and the component that enhanced the hydration reactivity was identified as Ca2SiO4 nanoparticles.