One-Pot Fabrication of Structurally Stable Cellulose Nanofibers/Biochar-Based Phase Change Composites with Enhanced Thermal Energy Conversion and Storage Capacity

The effective utilization of phase change materials (PCMs) with outstanding thermal conductivity, significant latent heat storage capacity, and exceptional form stability is essential for their functions in thermal energy conversion and storage systems. This work successfully developed form-stable composite phase change materials by combining cellulose nanofibers (CNFs) and biochar (BC) with polyethylene glycol (PEG) into CNF/BC/PEG aerogels using a single-step procedure. The resultant three-dimensional linked porous aerogels proficiently encapsulate PEG, inhibiting leakage by robust surface tension and capillary forces. These CNF/BC/PEG aerogels demonstrate improved thermal reliability, substantial loading capability, and exceptional form stability for the composite PCMs. The differential scanning calorimetry (DSC) investigation indicates that the phase transition enthalpy of these aerogels is notably high, varying from 135.15 to 154.53 J/g. Incorporating BC enhances thermal conductivity of aerogels to 39.5 mW/m·K, with PEG encapsulation achieving 92.6% and thermal storage efficiency at 86%. Furthermore, the composite aerogels exhibit notable thermal regulation properties and efficient thermal conversion and storage, as validated by a thermocouple prototype. These developed composite phase change aerogels have considerable potential for practical thermal storage and management applications.