Hierarchical carbon foams with tunable MOF nanostructure for improving solar-thermal conversion performance of phase change materials

Solid-liquid phase change materials (PCMs) suffer from liquid phase leakage, limited heat conductivity, and insufficient light absorption, which provide significant obstacles for solar energy storage. In this study, Zn–Co bimetallic ZIF structures with three morphologies were assembled on melamine foam (MF) by different synthesis conditions, followed by high-temperature carbonization to fabricate a hierarchical framework, in which ZIF-derived carbon layers integrated into carbonized melamine foam (CMF). Upon encapsulating energy storage unit paraffin wax (PW), the resultant CMF@Co–N/C/PW composite PCMs demonstrated superior encapsulation performance, enhanced thermal conductivity, excellent capacity for photothermal conversion and thermal storage. The hierarchical framework was comprised of ZIF-derived carbon nanostructures integrated with three-dimensional carbon skeleton, which provided a dual encapsulation effect and achieved a dimensional retention ratio of 95.71 %. Additionally, CMF@Co–N/C/PW exhibited a high phase change latent heat of 220.90 J/g and proved to be a reliable long-term thermal cycle system. Benefiting from the continuous carbon skeleton, CMF@Co–N/C/PW exhibited a noteworthy enhancement in thermal conductivity, showing a 100 % increase compared to pristine PW. More importantly, the impressive photothermal conversion efficiency of up to 93.65 % was attributed to the synergistic effects of Co nanoparticles, nitrogen-doped defective carbon, and multiple light scattering and absorption of the hierarchical network. The developed composite PCMs hold considerable promise in solar energy conversion applications.