Ion diffusivity and alkyl chain length-dependent triboelectric behavior of PVDF-HFP+IL composites

Abstract

As the global demand for renewable and clean energy solutions grows, triboelectric nanogenerators (TENGs) have emerged as a promising technology for harvesting mechanical energy. In this context, our study focuses on incorporating ionic liquids (ILs) into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to explore how the alkyl chain length of ILs influences triboelectric polarity. Imidazolium-based ILs containing bis(trifluoromethylsulfonyl)imide (TFSI⁻) anions were used, with cations such as 1-ethyl-3-methylimidazolium (EMIM⁺) and 1-butyl-3-methylimidazolium (BMIM⁺) exhibiting tribo-positive characteristics, while those with longer alkyl chains, including 1-methyl-3-n-octylimidazolium (OMIM⁺) and 1-dodecyl-3-methylimidazolium (DoMIM⁺), displayed tribo-negative behavior. These trends were correlated with self-diffusion coefficient measurements of the ILs. The control of triboelectric behavior and the formation of an electric double layer (EDL) through IL incorporation significantly enhanced the surface charge density, thereby improving the output performance of TENGs. This work provides a novel strategy for enhancing TENG efficiency and offers material selection guidelines for sustainable energy applications.