Triboelectric Nanogenerators of the Li Salt of Adipic Acid-Incorporated Poly(vinyl alcohol) Composites Toward Biomechanical Motion Energy Harvesting and in Sports Application

Mono-Li salts of adipic acid (Li-AA)-incorporated poly(vinyl alcohol) (PVA) composites were synthesized with the aim of utilizing them in triboelectric nanogenerators (TENGs). Fourier transform infrared (FTIR) spectroscopy revealed the formation of intermolecular H-bonding between the acid functional moiety of Li-AA and the hydroxyl functional group of PVA in the PVA/Li-AA composite and the simultaneous breakdown of interchain H-bonding of PVA. This led to a progressive decrease in glass transition temperature and melting temperature with a concomitant increase in onset and final degradation temperatures in the PVA/Li-AA composite with increased Li-AA concentration. The dielectric properties of the PVA/Li-AA composite manifested the influence of strong interfacial, dipolar, and ionic interactions in the presence of increased Li-AA concentration. Due to the higher surface roughness, flexibility, and increased dielectric constant of the PVA/Li-AA composite film, the TENG was fabricated in a vertical-contact-separation mode. Further, TENG was investigated for biomotion sensing and energy harvesting for various movements including knee bending, walking, jogging, etc. The open-circuit voltage in the PVA/Li-AA composite-based TENG of 15 wt % Li-AA registered ∼90 V and a short-circuit current of ∼45 μA. Moreover, the device showed a maximum power density of ∼2.75 W/m2 at 2 MΩ resistance. Additionally, the device also showed sensing output for writing and keyboard typing, and the fabricated TENG exhibited sensing output for boundary detection in lawn tennis sport.