Flame-retardant and form-stable phase change composites based on black phosphorus nanosheets/cellulose nanofiber aerogels with extremely high energy storage density and superior solar-thermal conversion efficiency
Impregnating organic phase change materials (PCMs) into cellulose-based aerogels is considered as an accessible and effective technology to prevent the liquid leakage issue due to the superior surface tension and capillary force. However, the poor solar-thermal conversion performance, low thermal conductivity, and high flammability still restrict the large-scale application of organic PCMs. Herein, two-dimensional (2D)-layered black phosphorus (BP) nanosheets having superior photothermal effect were synthesized from BP crystal through ultrasonication-assisted liquid exfoliation. Then, novel form-stable PCM composites (CBPCMs) were fabricated by impregnating n-octacosane into the cellulose nanofiber (CNF)/BP hybrid aerogels. The interconnected porous aerogels could adequately support the n-octacosane and effectively prevent the liquid leakage issue. Differential scanning calorimetry (DSC) analysis demonstrated that the synthesized CBPCMs based on CNF/BP hybrid aerogels possessed extremely high n-alkanes loading capacity and thermal storage density (247.0–251.6 J/g). The incorporation of BP nanosheets into the aerogels considerably increased the thermal conductivity (89.0% increase) and solar-thermal conversion and storage efficiency (up to 87.6%) of CBPCMs. Furthermore, with the increasing content of BP nanosheets in aerogels, the total heat release and heat release rate of the CBPCMs considerably decreased, while the LOI value and char yield increased, thus revealing the significantly improved flame retardancy for PCM composites. In conclusion, the CBPCMs show considerable potential in the solar energy utilisation field.