Electrospun Lignin-Based Phase-Change Nanofiber Films for Solar Energy Storage

Functional materials for solar energy collection, conversion, and storage need to be developed to address the global energy crisis. In this study, phase-change nanofiber films [PCNFs, sodium lignosulfonate (SLS)/polyvinyl alcohol (PVA)/polyethylene glycol (PEG)], which maintain their shape, were developed for solar-to-thermal energy conversion and storage. The films were constructed by electrospinning with PEG as the phase-change material, SLS/PVA mixture as the supporting matrix, and SLS as the photothermal material. SLS effectively improved the supporting property of the PCNFs owing to sturdy hydrogen bonds and electrostatic entanglement between its macromolecule chains and PVA/PEG, which prevented the leakage and transfer issue for PEG. Moreover, the PCNFs showed excellent solar-to-thermal energy conversion and storage ability, attributed to the π–π stacking of SLS molecules and the phase-change process, respectively. The SLS/PVA/PEG film with a PEG content of 32.43% exhibited a diameter of 465 ± 109 nm and a latent heat of fusion of 42.16 J·g–1, with a phase-change temperature of 45.20 °C. The film showed favorable stability over 50 heating–cooling cycles, thermal stability below 220 °C, good shape stability, and a solar-thermal energy conversion and storage efficiency of 18.03%. This study demonstrates a potential route to improve the utilization of lignin and solar energy and promotes the development of sustainable energy.