A high performance nanocellulose-PVDF based piezoelectric nanogenerator based on the highly active CNF@ZnO via electrospinning technology

Piezoelectric polymer composites have attracted much attention due to their high piezoelectric properties and excellent flexibility. In this work, cellulose nanofibers (CNF) were loaded with ZnO by an improved two-step hydrothermal method to obtain CNF@ZnO composites, which have the advantage at high-efficiency one-step film formation and displays considerable piezoelectric performance. Under the optimized hydrothermal conditions, ZnO can be uniformly loaded on CNF sbstrate. The piezoelectric response of CNF at scattered state and micro-nano scale has been successfully characterized to be 5.85 pm·V-1 via piezoelectric force microscopy (PFM), which can be increased to 9.49 pm·V-1 after loaded with ZnO. The obtained CNF@ZnO was dispersed in polyvinylidene fluoride (PVDF) to prepare a large-format tough PVDF/CNF@ZnO composite membrane (E-PVDF/CZ) by electrospinning. CNF@ZnO can effectively increase β phase in PVDF to be 87.36%, and its piezoelectric response was further enhanced to be 24.65 pm·V-1, along with longitudinal piezoelectric coefficient (d33) of 31±2.07 pC·N-1 higher than that of E-PVDF (20.25±2.05 pC·N-1). It also exhibits excellent mechanical performance and flexibility with the tensile strengthen of 16.12±2.35 MPa and elongation at break of 16.21±2.17%. Under the force of 45 N, the open-circuit voltage (VOC) and short-circuit current (ISC) of E-PVDF/CZ are as high as 11.8 V and 452 nA, respectively. Finally, the prepared flexible sensor has an VOC up to 31.2 V under the fist hitting state, while it is about 1.68 V stimulated by water droplets which can also weakly light a LED. The strategy will exactly facilitate the cellulose material in the application in energy harvesting and environmental monitoring.