Microstructural control by freeze-casting of CaO architectures for improved and stable thermochemical energy storage performance
Nabil Amghar, Juan Ivorra Martínez, Antonio Perejón, Dorian Hanaor, Aleksander Gurlo, J. Ramírez‐Rico, Luis A. Pérez‐Maqueda, Pedro E. Sánchez‐Jiménez
Abstract
This study investigates the development of porous calcium-based monoliths via freeze-casting (FC) as a novel approach for thermochemical energy storage, particularly within the Calcium Looping (CaL) process. The freeze-casting technique enabled the fabrication of scaffolds with controlled porosity using polyvinyl alcohol (PVA) as a binder. Experimental results demonstrated that freeze-cast monoliths exhibited superior multicycle performance under various carbonation and calcination conditions. The FC-CaCO 3 monolith achieved the highest residual conversion of 68.1 % under mild vacuum calcination conditions (780 °C, 0.1 bar CO 2 ), significantly surpassing other configurations. Tests conducted in an inert atmosphere also yielded favorable results, with a conversion of 56.1 %, outperforming equivalent raw powder samples. The enhanced performance is attributed to improved CO 2 interaction with the porous structure, mitigating sintering effects and preserving active surface area. Morphological observations by X-ray tomography and SEM confirmed limited particle sintering after multiple cycles, maintaining a reactive surface that supported consistent conversion rates. The pore size distribution of the material evolves upon cycling resulting in an increased microporosity, while the pore network maintains a low tortuosity (τ ~ 1.5–2.0). The addition of dopants such as ZrO 2 and SiO 2 did not enhance performance, as the monoliths' inherent structure provided sufficient stability. These findings highlight freeze-casting as a promising method for creating advanced porous materials suitable for energy storage applications.