Multifunctional composite phase change materials based on hydrate salt embedded in flame-retardant aerogel for efficient solar thermal energy storage

Hydrate-based phase change materials (PCMs) feature high energy storage density and low cost. However, their inherent drawbacks including liquid leakage, severe supercooling and low photothermal conversion efficiency limit their further application. To address these issues, a multifunctional composite PCM was fabricated by integrating flame-retardant aerogel skeletons with hydrate salts in this work. A composite aerogel support was first prepared via freeze-drying using polyvinyl alcohol (PVA), xanthan gum (XG), glutaraldehyde (GA), phytic acid (PA) and polydopamine-modified expanded graphite (EG@PDA) as raw materials. Sodium acetate trihydrate (SAT) was then loaded into the aerogel through melt impregnation. As a result of the three-dimensional porous and hydrophilic network, the composite resists leakage, suppresses crystal water loss, and reduces the supercooling degree of sodium acetate trihydrate (as low as 1.2 °C) without using additional nucleating agents. The composite achieves a phase change enthalpy of 210.65 J/g and retains 93.6% of its latent heat after 200 thermal cycles. The incorporation of modified expanded graphite provides continuous thermal conduction pathways, enhancing the thermal conductivity to 0.893 W/(m·K) (a 107% improvement) and giving a photothermal conversion efficiency of 85.39%. Furthermore, the composite shows no ignition and no molten droplet generation in vertical burning tests. This study provides a novel strategy for the widespread application of hydrate-based PCMs in thermal energy storage and thermal management.