Solar photothermal energy storage using phasechange 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 CaCO 3 /Fe 3 O 4 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 CaCO 3 -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. KEYWORDS: magnetic phase-change microcapsules, black phosphorus nanosheets, CaCO 3 /Fe 3 O 4 composite shell, core-shell structure, photothermal conversion efficiency, thermal energy storage

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