Porosity-tunable composite aerogels enabled by homogeneous phase change coating for photothermal energy conversion and storage

<p>Three-dimensional porous matrices loaded with phase change materials (PCMs) offer significant potential for photothermal energy conversion and storage. However, the composite materials prepared via vacuum impregnation suffer from low thermal conductivity. A novel phase change composite aerogel (PCCA) material is designed that simultaneously exhibits excellent thermal insulation and efficient photothermal energy conversion and storage, by leveraging the inherently low thermal conductivity of both porous materials and PCMs. PCCA constructed using biomass-derived templates demonstrates outstanding photothermal performance, achieving surface temperatures as high as 86 °C under 1 sun. A quantitative uniform coating impregnation method is developed based on the unique solid-liquid phase transition of stearic acid/ethanol mixture, which facilitates the quantitative regulation of porosity when loaded with stearic acid. PCCA50 achieves a porosity of 50%, a melting enthalpy of 182.1 J g<sup>-1</sup>, a crystallization enthalpy of 174.5 J g<sup>-1</sup>, and a thermal conductivity of 0.112 W m<sup>-1</sup> K<sup>-1</sup>, contributing to remarkable thermal insulation and energy storage capacity. Moreover, the nanoconfined space in PCCA provides kinetic constraints for the loading of stearic acid, leading to the coexistence of sub-stable and bulk-stable polymorphs. This enables PCCA to effectively resist temperature fluctuations across a broader photothermal temperature range.</p>