Morphological Observation of LiCl Deliquescence in PDMS-Based Composite Foams

Abstract

The LiCl-based heat storage system exhibits a high-energy density, making it an attractive and one of the most investigated candidates for low-temperature heat storage applications. Nevertheless, lithium chloride, due to its hygroscopic nature, incurs the phenomenon of deliquescence, which causes some operational challenges, such as agglomeration, corrosion, and swelling problems during hydration/dehydration cycles. Here, we propose a composite material based on silicone vapor-permeable foam filled with the salt hydrate, hereafter named LiCl-PDMS, aiming at confining the salt in a matrix to prevent deliquescence-related issues but without inhibiting the vapour flow. In particular, the structural and morphological modification during hydration/dehydration cycles is investigated on the composite foam, which is prepared with a salt content of 40 wt.%. A characterization protocol coupling temperature scanned X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM) analysis is established. The operando conditions of the dehydration/hydration cycle were reproduced while structural and morphological characterizations were performed, allowing for the evaluation of the interaction between the salt and the water vapor environment in the confined silicon matrix. The material energy density was also measured with a customized coupled thermogravimetric/differential scanning calorimetric analysis (TG/DSC). The results show an effective embedding of the material, which limits the salt solution release when overhydrated. Additionally, the flexibility of the matrix allows for the volume shrinkage/expansion of the salt caused by the cyclic dehydration/hydration reactions without any damages to the foam structure. The LiCl-PDMS foam has an energy density of 1854 kJ/kg or 323 kWh/m3, thus making it a competitive candidate among other LiCl salt hydrate composites.

Research Progress on Hygroscopic Agents for Atmospheric Water Harvesting Systems

“…LiCl has the strongest performance among the hygroscopic salts, but like calcium salts, both have similar drawbacks. LiCl is susceptible to deliquescence, agglomeration and clumping, corrosiveness, and swelling during the process of adsorption and resolution [53][54][55]. In summary, hygroscopic salts have the potential to be used in the production of freshwater [48] but to solve the above problems.…”

“…Traditional adsorbent materials such as zeolite and activated carbon are simple and inexpensive to prepare and thus are widely used in various fields [66,67], but the porous materials have poor hygroscopic properties and high-resolution temperatures [46,68]. Hygroscopic salt is prone to problems such as deliquesce, leakage, and agglomeration [53][54][55]. Figure 4 shows the moisture absorption principle diagram of a porous material-salt composite hygroscopic agent.…”

“…groscopic salt is prone to problems such as deliquesce, leakage, and agglomeration [53][54][55]. Figure 4 shows the moisture absorption principle diagram of a porous material-salt composite hygroscopic agent.…”

“…However, current research focuses on the amount of moisture absorbed per unit mass as the main parameter for evaluating moisture absorption performance [54,81,[85][86][87]. In actual use, volume is an important factor limiting the number of devices and materials used, so the amount of moisture adsorbed per unit volume of moisture-absorbing materials should also be used as one of the performance evaluation criteria, and this is related to the density of the material after adsorption.…”