Highly Efficient Thermal Energy Storage Using a Hybrid Hypercrosslinked Polymer**

Abstract In this work, an organic/inorganic hybrid polymer containing siloxyl functional groups was synthesized and applied to encapsulate phase change materials (PCMs). Owing to the mild conditions of the hypercrosslinking reaction, which only requires the addition of a catalytic amount of aqueous alkaline solution, both organic and inorganic PCMs are tolerated. It is noteworthy that the initial homogeneous state of the reaction mixture allowed the ultimate encapsulation rate of the PCMs and the uniform blending of the third nano‐additives with the aim of thermal conductivity enhancement. Further study reveals that the presence of this hybrid hydrophobic polymer in a phase change composite endows the latter with a unique self‐cleaning property. This novel PCM encapsulation protocol is suitable for nanoparticles including carbon‐based nanomaterials, metal oxide nanoparticles, and inorganic oxide nanoparticles. A thermal conductivity enhancement of 600 % was achieved along with 93.7 % light‐to‐thermal conversion efficiency with a latent heat of 180 J g −1 without leakage.