Integration of Magnetic Phase-Change Microcapsules with Black Phosphorus Nanosheets for Efficient Harvest of Solar Photothermal Energy

Solar photothermal energy storage using phase-change material (PCMs) provides sustainable penetration in comprehensive utilization. However, PCMs are obliged to suffer from low conversion and storage effectiveness in solar photothermal energy due to a low optical absorption capacity. In this study, we developed a type of magnetic phase-change microcapsule system with superior photothermal energy conversion efficiency. The microcapsule system was constructed with n-docosane as a PCM core and a CaCO3/Fe3O4 composite shell surface-decorated with black phosphorus (BP) nanosheets employing a Pickering emulsion-templated precipitation technique. The presence of BP nanosheets on the capsule surface not only enhanced the emulsion stability to facilitate the fabrication of a tight CaCO3-based shell, resulting in a high latent heat capacity of the microcapsules, but also improved thermal conduction of the microcapsule system, promoting a fast thermal response and heat transfer. The microcapsule system shows a high phase-change enthalpy of over 120 J/g and a significant increase in thermal conductivity by over 400% compared to pure PCM. More importantly, the microcapsule system exhibits a high photothermal conversion efficiency of 95.08%, which is superior to most of the PCM-based composite materials reported in the literature. There is only 0.02% conversion efficiency lost after the 10-cycle photothermal conversion experiment for the microcapsule system, indicating a good working stability for the long-term use of solar photothermal conversion and storage. By decorating magnetic phase-change microcapsules with BP nanosheets on the shell, this study offers a new strategy for development of PCM-based composite materials for efficient harvest and utilization of solar energy.