Synergistic effect of sepiolite as an active binder for enhancing mechanical stability of porous K2CO3 granules in thermochemical heat storage

In thermochemical heat storage, higher adsorbent porosity improves reaction kinetics by facilitating mass transfer but compromises mechanical stability. This study addresses this challenge by incorporating 5–20 wt% sepiolite to reinforce porous potassium carbonate (K${}_2$CO${}_3$) granules while preserving reaction efficiency. Specifically, KS20 granules, containing 20 wt% sepiolite, exhibited a substantial increase in maximum compressive load from 26.8 N to 48.4 N, strengthening cohesion within the K${}_2$CO${}_3$ granules. At the material level, KS20 granules demonstrated a volumetric energy density of 0.9 GJ/m${}^3$. The partial substitution of K${}_2$CO${}_3$ with sepiolite had minimal impact on the total hydration energy density, as sepiolite actively contributed to adsorption through physisorption. In addition, its mesoporous structure retains moisture internally, preventing agglomeration. KS20 granules exhibited excellent cyclability, with stable structural integrity and resistance to agglomeration, ensuring minimal material loss and performance degradation over multiple cycles. Moreover, they maintain their effectiveness under varying environmental conditions, reducing the risk of unwanted reactions or physical breakdown during storage and transportation.