A facile method to enhance the flexibility and triboelectric output of PDMS using ionic liquid-coated single-wall carbon nanotubes

Energy harvesting devices based on triboelectric effect have gained much attention recently due to their significant potential in low-frequency applications, especially in wearable electronics. To enable these devices, flexible materials with relatively high electrical conductivity and large triboelectric output are needed. In this study, a PDMS composite is fabricated using embedded ionic liquid (IL) coated single-wall carbon nanotubes (SWCNTs). The ratio of IL to SWCNTs is tuned to achieve the desired material properties for wearable triboelectric nanogenerators. The SWCNT-IL-PDMS (IL: SWCNT= 20:1) composite exhibits a relatively high electrical conductivity (0.004 S/m) and an enhanced triboelectric output compared to unmodified PDMS. Specifically, the open-circuit voltage (Voc) and the short-circuit current (Isc) are increased by three folds. The relatively high electrical conductivity enables the composite to transfer charges without electrodes and reduces the internal impedance of triboelectric nanogenerators. The flexibility of the composite is also improved, as demonstrated by the decrease in both the tensile and compressive elastic moduli. In addition, the mechanism behind the change in electrical properties and triboelectric output is proposed and discussed in this paper. Specifically, the increase in the dielectric constant and electrical conductivity of the composites with IL is likely due to the better dispersion of SWCNT in the polymer matrix, and the change in the triboelectric output is a result of (1) the trade-off between dielectric constant and electrical conductivity, and (2) the shifting of triboelectric polarity with the addition of IL. This study not only provides a facile method to simultaneously increase the flexibility, electrical conductivity, and triboelectric output of polydimethylsiloxane (PDMS), but also generalizes the approach and paves the way to explore new flexible and electrically conductive materials for wearable triboelectric nanogenerators.