Enhanced thermal conductivity of PEG/diatomite shape-stabilized phase change materials with Ag nanoparticles for thermal energy storage

Ag nanoparticles (AgNPs) are a promising additive because they can enhance the thermal conductivity of organic phase change materials. In this paper, a series of high thermally-conductive shape-stabilized phase change materials (ss-PCMs) were tailored by blending PEG with AgNP-decorated diatomite. In order to enlarge its pore size and specific surface area and make it a suitable PEG carrier, the effect of alkali leaching on the microstructure of diatomite was studied. While PEG melted during phase transformation, the maximum load of PEG could reach 63 wt%, which was 31% higher than that of the raw diatomite. Spherical-shaped crystalline AgNPs with a diameter range of 3-10 nm were uniformly decorated onto diatomite. The XPS results for this material proved that the valence state of silver in the PEG/diatomite PCM was mainly zero. The phase change enthalpy of the PEG/diatomite/Ag PCM reached 111.3 J g(-1), and the thermal conductivity of the PEG/diatomite PCM containing 7.2 wt% Ag was 0.82 W m(-1) K-1, which was 127% higher than that of the PEG/diatomite composite. The reduced melting and freezing periods indirectly proved that heat transfer in the composite material during the heat storage and release process was enhanced through the thermal conductivity improvement. The composite PCM was thermally and chemically stable even after 200 cycles of melting and freezing. This indicated that the resulting composite PCMs were promising candidate materials for building applications due to their large latent heat, suitable phase change temperature, excellent chemical compatibility, improved supercooling extent, and high thermal stability.