To address these limitations, our previous study developed an initial encapsulation approach using titanium dioxide (TiO₂) as a shell material via a microemulsion system. While the resulting TiO₂-coated KF·4H₂O particles showed improved structural stability and leakage prevention, the TiO₂-based encapsulation offered moderate improvement in thermal conductivity and did not fully resolve the supercooling issue.
In the present work, we report an improved encapsulation strategy employing copper oxide (CuO) as the shell material. Using a microemulsion approach comprising a mixture of oil, water, and surfactants, CuO-encapsulated KF·4H₂O core–shell structures were synthesized under controlled conditions, with copper ethoxide (Cu(OC₂H₅)₂) as the precursor for CuO formation. The CuO coating, which has about 4 times higher thermal conductivity than TiO₂, was used to enhance heat transfer efficiency. By adjusting the synthesis temperature within the range of 0°C to 50°C, particle sizes were tunable from 100 nm to 3 µm, allowing further optimization for different system requirements. The encapsulated structures also exhibited high energy density, with a latent heat of approximately 160 J/g, corresponding to about 80% of the theoretical capacity of pure KF·4H₂O. The heterogeneous nucleation potential of the CuO shell successfully decreased the supercooling degree from approximately 20°C to below 10°C. Thermal cycling experiments confirmed that the encapsulated structures maintained their latent heat capacity and structural integrity without leakage.