Surface Morphology and Structural Organization Effects in Cellulose Nanofibril Papers for Triboelectric Nanogenerators

ABSTRACT Sustainable energy harvesting technologies require materials that combine high performance with environmental compatibility. Triboelectric nanogenerators (TENGs) provide a versatile platform for converting mechanical energy into electricity, yet the structure–property relationships governing bio‐derived materials remain insufficiently understood. Cellulose nanofibrils (CNFs), with their structure and tunable interfaces, offer a promising materials platform to address this challenge. In this study, CNF papers were engineered via controlled filtration, pressing, and ionic liquid (IL) posttreatment to systematically investigate the roles of surface morphology and crystallinity. Multiscale characterization using atomic force microscopy (AFM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), and attenuated total reflectance Fourier transform infrared (ATR–FTIR) spectroscopy showed that reducing surface roughness from ∼50 to ∼18 nm enhanced the power density from ∼5.7 to 13 W m −2 by increasing the effective contact area. Further structural modulation via IL reduced roughness to ∼7 nm and crystallinity from ∼61% to ∼49%, and a partial polymorphic transition from cellulose I to cellulose II at the fibril level was induced, resulting in a pronounced performance enhancement. The optimized CNF‐based TENG achieved a power density of ∼80 W m −2 and could power 100 blue light‐emitting diodes under manual tapping. These results highlight the synergistic roles of interfacial smoothness, structural disorder, and cellulose polymorphism, providing design guidelines for high‐performance sustainable triboelectric energy devices.