Flame-retardancy cellulosic triboelectric materials enabled by hydroxyl ionization

Triboelectric nanogenerators (TENGs) are among the most promising available energy harvesting methods. Cellulose-based TENGs are flexible, renewable, and degradable. However, the flammability of cellulose prevents it from being used in open-flame environments. In this study, the lattice of cellulose was adjusted by the hydroxyl ionization of cellulose molecules, and Na⁺ was introduced to enhance the flame retardancy of cellulose nanofibers (CNFs). The experimental results showed that the amount of hydrogen bonding between cellulose molecules increased with the introduction of Na⁺ and that the limiting oxygen index reached 36.4%. The lattice spacing of cellulose increased from 0.276 to 0.286 nm, and the change in lattice structure exposed more hydroxyl groups, which changed the polarity of cellulose. The surface potential of the fibers increased from 239 to 323 mV, the maximum open-circuit voltage was 25 V·cm⁻², the short-circuit current was 2.10 µA, and the output power density was 4.56 µW·cm⁻². Compared with those of CNFs, the output voltage, current, and transferred charge increased by 96.8%, 517%, and 23%, respectively, and showed good stability and reliability during cyclic exposure. This study provides a valuable strategy for improving the performance of cellulose-based TENGs.