3. Conclusions
Kraft, hydrophilic, and hydrophobic lignins were prepared, followed by
an electrospinning process. The electrospun nonwoven kraft, hydrophilic,
and hydrophobic lignin nanofibers (NFs) were evaluated as tribopositive
materials of triboelectric nanogenerators (TENGs). The enhancement in
the surface energy of hydrophilic lignin NFs enabled the TENG to exhibit
an outstanding output voltage over 95 V at a tapping force and frequency
of 9 N and 9 Hz, respectively. The energy-harvesting efficiency, which
considered the output voltage with the size and applied tapping
conditions of the tested TENG, was 4133 V N-1m-1, showing the highest value among the other
previously-reported biomaterial-based TENGs. Furthermore, a TENG
entirely based on both tribo-positive and -negative lignin NFs was
demonstrated, which also exhibited a reasonable energy-harvesting
performance at user-engaged activities, such as walking and running.