Impact of Relative Humidity on Sorption Performance of K2CO3-Based Composites for Low-Temperature Thermochemical Energy Storage

This study investigated the sorption performance of the expanded vermiculite (EV)/K2CO3 composite sorbent across varying relative humidity conditions, employing dynamic vapor sorption experiments to analyze sorption kinetics and thermodynamic properties. The results highlight the substantial influence of relative humidity on the sorption behavior and thermal energy storage capacities of the composite sorbent. At lower humidity levels, the sorbent predominantly absorbs water through a chemisorption process, with an observed enhancement in the sorption reaction rate with increasing relative humidity levels. Nevertheless, at higher humidity levels, K2CO3 undergoes deliquescence, forming a salt solution that substantially enhances water uptake. This variation in relative humidity profoundly influences both the sorption process and the ultimate water uptake. Moreover, the inclusion of the EV matrix effectively disperses K2CO3 salt particles and facilitates water vapor transport, thereby delaying deliquescence and enabling smooth solution absorption even under high humidity conditions. Notably, the heat storage capabilities of the composite sorbent are also significantly influenced by relative humidity levels, leading to a substantial rise in hydration heat and volumetric heat storage density in high humidity environments. Hence, it is advisable to select the sorbent dosage and operational parameters with caution, taking into consideration fluctuations in environmental humidity to achieve optimal outcomes in practical applications.