Eutectic crystallohydrate PCM@halloysite nanocontainer composite system was fabricated to eliminate the phase separation of crystallohydrates as phase change materials as well as to improve their thermal stability over phase change cyclings. The mixture of Na2HPO4 *12H2O (DHPD) and Na2SO4*10H2O (SDH) was selected as crystallohydrate PCM (EHS) because of their ability to form stable eutectic hydrated salts with low melting temperature (40 0C) suitable for domestic heat range. Halloysites as nanocontainers have the advantages of low-cost and easy accessibility. They have long nanotubular morphology with the average inner diameter of 30 nm, the average shell thickness of 20 nm and the tube length ranging from 200 nm to 1 µm. This provides nano-confinement effect on the loaded crystallohydrate PCMs, which can be proven by the improved phase change performance and cycling stability. Meanwhile, the proper ratio of inner diameter to shell thickness endows halloysite as nanocontainers high loading capacity as well as structural stability. Due to the vacuum impregnation process and the electrostatic interaction between Al-OH from the inner alumina layer and P-O from eutectic hydrated salts mixture. The composite with 67% efficient loading of DHPD and SDH in 1:1 mass ratio exhibits no phase separation during heat uptake/release. Its melting temperature retains around 35 °C and the melting enthalpy decreases only by 7% from 142 J/g to 132 J/g after 50 cycles. Similar results have been found for sepiolite as matrix material to load EHS (mass ratio 50% DHPD: 50% SDH) to form EHS@sepiolite composites. The unique structure of sepiolite determines its characteristics of very high specific surface area of 156.82 m2/g and big pore volume of 0.64 cm3/g, which enables its high loading capacity of PCM. The EHS@sepiolite composite with 88% effective loading was successfully fabricated. The structural characterization shows the crystal structures of both sepiolite and EHS are well kept in the composite. No covalent bonding is formed between PCM and matrix. The composite has the high melting enthalpy of 185 J/g, and the melting temperature of 38.1 °C. Considering the low cost and abundant reserve of sepiolites and halloysites, the simple fabrication procedure, the high loading efficiency and the good cycling stability, heat storage nanocomposites have big potential in thermal energy storage application in low temperature range.

Use of the multifunctional phase change materials based on natural clays as rechargeable thermal batteries for distant transfer of thermal energy

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.