Triboelectric Nanogenerators Based on Ulvan Biopolymer: Impact of Lithium Sulfate Doping on Electrical Output

The increasing demand for sustainable energy solutions has driven extensive research into energy harvesting devices, such as triboelectric nanogenerators (TENGs). Although various additives, including nanowires and salts, have been investigated to enhance the performance of biopolymer-based TENGs, the use of lithium salts in green algae-based TENGs remains unexplored. Herein, a series of TENGs are fabricated using ulvan, a biopolymer derived from the green algae Ulva nematoidea. To improve the output performance of these TENGs, the ulvan matrix is doped with lithium sulfate (Li₂SO₄) at concentrations of 0%, 10%, 20%, 30%, 40%, and 50% by weight. Dielectric permittivity measurements are conducted to calculate the surface charge density. The results show an increase from 0.94 nC cm⁻² for the pristine film to 1.14 nC cm⁻² at 30 wt% Li₂SO₄, beyond which further increases in salt concentration lead to a decrease in charge density. The incorporation of salts significantly enhances the electrical performance, with the 20% Li₂SO₄/ulvan device achieving a maximum power density of 0.156 W m⁻², representing an 85.7% improvement compared to the pristine ulvan TENG. The open-circuit voltage (V_oc) and short-circuit current also increase with salt concentration, with V_oc reaching 87.71 V at 30% Li₂SO₄.