Nb₂CT_x MXene/Delignified Wood–Supported Phase-Change Composites with Desirable Photothermal Conversion Efficiency and Enhanced Flame Retardancy for Solar–Thermal Energy Storage

Abstract

Although organic phase-change materials (PCMs) have been widely used for thermal energy storage, their high flammability, poor photothermal conversion efficiency, and liquid leakage issues severely restrict their practical applications in solar−thermal fields. Herein, novel formstabilized composite PCMs (CMPCMs) with high energy storage density, excellent flame retardancy, and desirable photothermal conversion efficiency were prepared by impregnating n-docosane into phytic acid (PA)/melamine (MEL)-modified Nb 2 CT x MXene/delignified wood (CMDW) under vacuum assistance. The interconnected three-dimensional porous CMDW supported n-docosane and avoided PCM leakage, owing to its strong surface tension and capillary forces. Differential scanning calorimetry analysis revealed that the CMPCMs exhibited satisfactory encapsulation ratios (up to 91.6%) and superior energy storage densities (190.2−219.5 J/g). Decorating delignified wood through Nb 2 CT x MXene nanosheet deposition considerably improved the solar−thermal conversion efficiency (up to 89.5%). Furthermore, with the increasing content of PA and MEL in the composites, the total heat release and peak heat release rate of the CMPCMs decreased remarkably due to the synergistic nitrogen−phosphorus flame-retardant mechanism, suggesting improvement in the flame-retardant properties of the CMPCMs. Overall, the shape-stabilized composite CMPCMs demonstrate tremendous potential for solar−thermal conversion and thermal management applications.