A shape-stable phase change composite prepared from cellulose nanofiber/polypyrrole/polyethylene glycol for electric-thermal energy conversion and storage

The design of shape-stable phase change composites (PCCs) with electrothermal conversion/storage performance provides a new direction for their potential applications in advanced electric energy storage. Herein, a cellulose nanofiber sponge coated with polypyrrole (PPy@CNF) was constructed and used to incorporate polyethylene glycol (PEG) to afford the PPy@CNF-PEG composite. The resulting PPy@CNF-PEG composite exhibited good shape-stable property and high melting enthalpy (169.7 J/g). Even when compressed at 440 times its own weight, the composite still maintained its original shape and gave off no molten PEG. By applying small voltages (1.75-1.9 V), it was also shown that the composite converted electricity to heat with efficiencies (up to 85.1%). This work demonstrates a simple, effective and general strategy to prepare biomass-derived composites with high electrothermal conversion efficiency for smart electric devices devoting to energy conversion and storage.