Enhanced photothermal conversion capability of melamine foam-derived carbon foam-based form-stable phase change composites

Carbon foams, which can be fabricated from melamine foams via direct carbonization, are promising supporting skeletons for phase change composites due to their excellent light absorption and form-stable features in photothermal conversion and storage. Carbonization temperature and time are two critical parameters during the carbonization process. However, most previous works usually considered the influence of carbonization temperature or time. As an improvement, this work simultaneously studies the impacts of carbonization temperature and time on the hypothesis of their synergetic effects on the mechanical, thermal, and optical properties of the melamine foam-derived carbon foams, aiming to determine the optimal carbonization process. The results indicated a critical carbonization temperature of approximately 350 °C, below which melamine foams could be partially carbonized even by extending the carbonization time to 180 min, leading to the low light absorption capability. Once exceeding 350 °C, the absorbance of the synthesized carbon foams in the solar spectrum was improved by more than 12.6%, mainly due to the super conjugated π bonds and C–C bonds formed within the carbon foams. With a further increase in the carbonization temperature, the charging efficiency of the phase change composite was slightly increased by 1.7%, but the mechanical strength of the carbon foams was declined by 38.4%. Besides, carbonization time presented a negligible effect on the charging efficiency. The optimal carbonization temperature and time were determined to be 350 °C and 5 min, respectively, and the corresponding charging and discharging efficiencies were 90.1% and 90.7%, demonstrating the excellent photothermal conversion performance of the proposed carbon foam-based phase change composites.