Cellulose nanofiber/melanin hybrid aerogel supported phase change materials with improved photothermal conversion efficiency and superior energy storage density

Organic phase change materials (PCMs) have been widely applied in thermal energy storage fields due to their good structural stability, high energy storage density, adjustable phase change temperature and non-toxicity. However, the poor solar-thermal conversion performance and structure stability restrict the large-scale application of organic PCMs. Herein, novel PCM composites (CMPCMs) with good structural stability, improved photothermal conversion efficiency, and superior energy storage density were successfully synthesized by impregnating poly (ethylene glycol) (PEG) into cellulose nanofibers/melanin hybrid aerogel. The three-dimensional (3D) aerogel framework had good shape stability and strong encapsulation ability, which inhibited the leakage of PEG and enhanced the shape stability of the synthesized PCM. The differential scanning calorimetry (DSC) results showed that CMPCMs exhibited relatively high melting enthalpies ranging from 168.3 to 175.9 J/g, and the introduction of melanin almost unchanged the energy storage density of the synthesized PCM composites. Simulated sunlight tests revealed that the introduction of melanin significantly improved the photothermal conversion efficiency of CMPCMs (from 47.2 to 85.9%). The thermal cycling test and thermogravimetric analysis showed that CMPCMs possessed excellent thermal stability and good encapsulation ability. In conclusion, the synthesized CMPCMs showed great potential in the practical utilization and storage of solar energy.