Characterization and performance analysis of scalable SrCl2@activated alumina composite sorbents for low-temperature thermochemical heat storage

Scalable SrCl 2 @Al 2 O 3 composites with tunable salt loadings are synthesized. • SA35 composite achieves a high energy density of 234.2 kWh/m 3 under winter conditions. • Solid-state hydration provides 23 °C thermal upgrading vs. 10.7 °C for solution sorption. • SA35 shows 9.24% loss after 30 adsorption cycles but 20.89% loss in sorption mode. • A temperature-pressure equilibrium phase diagram of the composite is constructed. Salt hydrate-based thermochemical energy storage (TCES) represents a promising pathway toward a sustainable energy future. In this work, a series of scalable strontium chloride@activated alumina (SrCl 2 @AA) composite sorbents with tunable salt loadings (up to 31.7 wt% for SA35) are developed via a facile vacuum impregnation method. Microscopic characterization analysis confirms that SrCl 2 crystals are effectively dispersed within the mesoporous architecture of the AA host, which successfully mitigates salt agglomeration and provides an extensive gas-solid interface for vapor transport. The experimental results manifest that under winter heating conditions, i.e., adsorption temperature ( T ads ) of 30 °C and evaporation temperature of 5–12 °C, the optimal SA35 composite delivers a high volumetric-energy storage density ( ESD v ) of 216.3–234.2 kWh/m 3 , and even at an elevated T ads of 45 °C, which is suitable for domestic hot water production when considering the exothermic effect, it maintains a considerable ESD v of around 120 kWh/m 3 . Solid-state hydration mode of SA35 provides thermal upgrading of 23 °C and an exergy density of 17.02 kWh/m 3 at T ads of 35 °C, outperforming the solution-absorption mode. Over 30 adsorption-desorption cycles, SA25 and SA35 show only 9.28% and 9.24% loss in ESD v , confirming superior cyclability. While the combined sorption regime (hydration plus solution-absorption) further boosts ESD v , SA35 suffers a 20.89% decline due to progressive liquid leakage. The Phase diagram reveals that the SA35 composite exhibits higher equilibrium vapor pressures than the pure salt, suppressing deliquescence and narrowing the metastable zone width. This work provides theoretical guidance for the fabrication and optimization of scalable TCMs for efficient salt hydrate-based TCES. Download: Download high-res image (236KB) Download: Download full-size image