Impact of porous host materials on the compromise of thermochemical energy storage performance

Thermochemical energy storage (TCES) systems address renewable energy intermittency with high energy density and negligible heat loss. CaCl2, known for its high reaction enthalpy and cost-effectiveness, faces challenges such as deliquescence and poor mass transfer. Incorporating porous host materials mitigates these issues. This study examines the impact of pore structure on TCES performance at both particle and reactor scales, utilizing five porous composites prepared via vacuum impregnation with vermiculite (V), expanded perlite (EP), pumice (Pm), silica gel (SG), and zeolite 13x (Z) as host materials. At the particle scale, macroporous composites (V-CaCl2, EP-CaCl2) achieved high gravimetric salt contents (>65%) and moderate volumetric energy density (0.55–0.65 GJ/m3) but exhibited slower reaction kinetics. Mesoporous SG-CaCl2 composite exhibited superior reaction rates and equilibrium hydration capacity, achieving sustained high-temperature output with an average temperature rise of 16.01 °C under RH=50%, albeit with a significant pressure drop across a 5 cm thick reaction bed, with a 0.2 m/s cross-sectional air velocity (101.06 Pa). EP-CaCl2 provided a balance of smooth heat release, low resistance (6.88 Pa), and favorable volumetric energy density (0.65GJ/m3). These findings underline the necessity of selecting appropriate porous host materials to optimize specific performance metrics such as energy density, reaction kinetics, and system-level thermal output characteristics, providing a pathway for designing more efficient and application-specific TCES systems.