Self-assembled cellulose nanofibers/graphene aerogel-supported phase change composites with a three-dimensional network structure for enhanced solar-thermal energy conversion and storage.

The complex preparation process, use of toxic reagents, and high cost are significant challenges associated with graphene-based composite phase change materials (PCMs). One of the objectives of this research is to prepare cellulose nanofibers (CNFs)@graphene aerogel (GA) using a hydrothermal method followed by freeze-drying. The ultimate goal is to explore the effect of incorporating CNFs@GA into polyethylene glycol (PEG) to form PEG/CNFs@GA composites. The results showed that a three-dimensional network structure of CNFs@GA was successfully constructed during the hydrothermal reduction process. Additionally, the CNFs@GA removed residual oxygen-containing groups and repaired lattice defects in the reduced graphene oxide. PEG was encapsulated through hydrogen bond interaction between CNFs@GA and PEG, resulting in the formation of PEG/CNFs@GA composites. Among all the PEG/CNFs@GA samples, PEG/CNFs@GA-4 exhibited excellent thermal energy storage, solar-thermal conversion efficiency, and thermal cycling stability. This performance is attributed to its high energy storage density of 167.5 J/g, solar-thermal efficiency of 91.03%, and slight phase change enthalpy loss of only 3.34% after 100 thermal cycles. The proposed hydrothermal strategy provides valuable insights into the development of next-generation photothermal PCMs with low cost, green synthesis, and tunable structure for efficient solar energy utilization.