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Thermochemical energy storage using a calcium oxide/calcium hydroxide/water (CaO/Ca(OH)2/H2O) reaction system is a promising technology for thermal energy storage at high‐temperatures (400°C‐600°C). The purpose of this study is to develop a practical composite material by enhancing heat transfer through the reaction bed and mitigating problems of pure CaO/Ca(OH)2 materials, such as formation of centimeter‐scale agglomerates and change in the bulk volume during repetitive reactions. The present study focused on a novel composite material using a silicon carbide/silicon (SiC/Si) foam. In the literature, performance of thermochemical energy storage of the composite using the ceramic foam remains unclear. In this study, we evaluated the performance of the composite material (~63 g) by a 100‐W‐scale packed bed reactor. The volumetric heat output rate (for the first 5 minutes, under maximum hydration pressure) of the composite was 1.3 kW L‐bed−1, which was 1.4 times higher than that previously reported for a bed of pure Ca(OH)2 pellets. The composite material, in which the CaO/Ca(OH)2 samples were subdivided inside pores with a mean diameter of 400 μm, retained high reactivity during cycle reactions, and maintained its bulk volume. Therefore, the composite material developed in this study shows promising application for high‐temperature thermochemical energy storage.

Thermochemical energy storage (TCES) using reversible gas‐solid reactions is a promising technology owing to the high energy density and capability of long‐term storage. TCES using a calcium oxide/calcium hydroxide/water (CaO/Ca(OH)2/H2O) reaction system has attracted considerable attention because of the low material cost and environmental friendliness of the reactants. Previous experimental studies have focused on the TCES performances of packed beds of calcium oxide/calcium hydroxide powder. However, pelleted materials can be more favorable than powdered materials from a practical viewpoint. The aim of this study is to evaluate the performance of TCES of a packed bed of calcium oxide/calcium hydroxide pellets. In this work, a total of 60 g of calcium hydroxide pellets (diameter of 1.9 mm and length of 2‐10 mm) was evaluated using a 100‐W scale packed bed reactor. The heat storage density of the bed was 1.0 MJ L‐bed−1, and an average heat output rate of 0.71 kW L‐bed−1 was observed for the first 10 minutes under a hydration pressure of 84.6 kPa. The stability of the reaction conversion of the bed was demonstrated during 17 cycles of experiments.

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