A wood fiber-based multifunctional generator for multiple environmental energy harvesting

Natural lignocellulose has asymmetric crystal structures and abundant oxygen-containing groups, which endow cellulose materials with piezoelectric and moist-electric properties. In this work, micron-scale wood fiber was oxidated by using 2,2,6,6-tetramethylpiperidine (TEMPO), then the tracheid structure of fiber produced cracks accompanied by exposing more active groups of hydroxyl groups inside the tracheid. ZnO was also grown on the tracheid by one-step hydrothermal method to construct a coaxial structure to enhance the piezoelectric performance of fiber/ZnO piezoelectric generator (PEG). The assembled fiber/ZnO-PEG can produce an open-circuit voltage (V OC ) of 5.5 V and a power density of 21.57 μW cm −3 under a cyclic force of 50 N at 2 Hz. In addition, according to hydrophilic properties of the fiber/ZnO composite film, it was also assembled into a moist-electric generator (MEG) by constructing an asymmetric electrode. The fiber/ZnO-MEG can generate the V OC of 0.47 V at 85 % RH. After connecting five 11CZ-2ZnO-MEGs in series, the LCD (liquid crystal display) and LED (light emitting diode) can be successfully lit. Moreover, when the assembled fiber/ZnO MEG was pasted on the wrist, the output electrical signals increase significantly during wrist bending process, which can be attributed to the moist-electric effect and piezoelectricity. The proposed energy harvesting device has the advantages of low cost, biocompatibility and biodegradability, which displays great potential in the field of green energy, as well as provides reference for multi-angle design of sensing device.