Morphology-controlled synthesis of Cu2O encapsulated phase change materials: Photothermal conversion and storage performance in visible light regime

• Morphology-controlled synthesis of Cu 2 O encapsulated phase change materials. • A possible morphology-controlled mechanism was proposed based on DFT calculations. • The synthesized microcapsules possessed latent heat of 82.9-148.9 J/g. • Facet-dependent visible light absorbance of the microcapsules was revealed. • The octahedral microcapsule showed photothermal conversion efficiency of 82.65%. Microencapsulated phase change materials (MPCMs) are usually limited in photothermal conversion due to their poor visible light absorbability and low thermal conductivity. Owing to a direct band gap of 2.0-2.2 eV, the semiconductor cuprous oxide (Cu 2 O) has attracted intense interest in solar energy harvest. Shape-dependent optical properties of Cu 2 O semiconductors are mainly focused on crystals enclosed by three low-index facets ({100}, {110} and {111}). Here, we successfully design and fabricate the Cu 2 O encapsulated MPCMs from cube, truncated cube, 26-hedron, and truncated octahedron to octahedron under precise control of NaOH. A possible growth mechanism to explore the correlation between selective adsorption of OH - on Cu 2 O facets and MPCMs shape evolution is suggested based on density functional theory calculations. The thermal analysis shows that the octahedral MPCMs enclosed by {111} facets possess latent heat of 148.9 J/g and photothermal conversion efficiency of 82.65% under irradiation of visible light. Differential scanning calorimeter (DSC) profiles of the MPCMs maintain good coincidence with only a slight fluctuation of phase transition temperatures and the associated enthalpies during the 200-cyclic scans, demonstrating excellent phase change reversibility and thermal durability. Our studies unambiguously provide a strategy for tailoring the optical properties of MPCMs to greatly harvest solar energy for green building materials, anti-ice coating etc. in the future.