Dielectric control of porous polydimethylsiloxane elastomers with Au nanoparticles for enhancing the output performance of triboelectric nanogenerators

Abstract

Taking advantage of the triboelectrification effect and electrostatic induction, triboelectric nanogenerators (TENGs) provide a simple and efficient path to convert environmental mechanical energy into electric energy. Since the generation of surface charges and their density on triboelectric materials are the key factors in determining TENG performance, many efforts have been undertaken to engineer the structures and chemistry of triboelectric materials. Among others, dielectric control of triboelectric materials is an emerging approach because the dielectric constant is intimately correlated with the capacitance of materials. In this regard, we prepared porous polydimethylsiloxane (PDMS) composites decorated with Au nanoparticles (NPs), which was designed to engineer the compressibility and dielectric constant of PDMS elastomer. To this end, a polydopamine layer was synthesized on the PDMS surface to facilitate the homogeneous deposition of Au NPs. Unlike untreated PDMS sponges, Au NPs were efficiently coated onto polydopamine-treated PDMS sponges to increase the dielectric constant. When the resulting porous NP-PDMS composites were assembled into TENG devices, the electrical output of the TENGs initially improved but decreased with the amount of Au NPs. This trade-off relationship has been discussed in terms of charge generation on the air surface and pores of NP-PDMS composites based on a recent experimental model.

Fig. 1. (a) Photographs of the sugar template and replicated PDMS elastomer. (b) Plan-view SEM image of the porous PDMS sponge. (c and d) TEM image (c) and UV-Vis spectrum (d) of the synthesized Au NPs. The DLS results with Gaussian fittings before (red color) and after (blue color) centrifugation-based purification are shown in Fig. 1d.

Fig. 2. (a) ATR-FTIR spectra of PDMS sponges with the introduction of PDA polymers and Au NPs. The PDMS/PDA was immersed in the NP solution for 24 h. (b) Time-dependent UV-Vis spectra after the immersion of PDMS (red color) and PDMS/PDA (blue color) in the NP solution. (c) Photographs of PDMS (i), PDMS/PDA (ii), PDMS/PDA/Au with different immersion times (iii), and PDMS/Au in the absence of PDA (iv). (d–f) Cross-sectional FE-SEM images of PDMS/PDA/Au sponges after immersion in NP solution for different times. (g) Cross-sectional FE-SEM images of PDMS/Au sponges after immersion in NP solution for 60 h.

Fig. 3. (a) Open-circuit voltage and (b) short-circuit current of TENG devices prepared by flat PDMS (black), PDMS sponge (red), PDMS/PDA (blue), PDMS/Au (green), and PDMS/PDA/Au (purple) composites. (c) Open-circuit voltage and (d) short-circuit current of the TENG devices prepared by PDMS/PDA/Au composites under different immersion times. The structure of the TENG device is also included in the scheme.

Fig. 4. (a) Frequency-dependent dielectric constant and loss tangent of PDMS sponge (green), PDMS/PDA (blue), and PDMS/PDA/Au (red) composites. (b) Average dielectric constant of PDMS/PDA/Au composites with different immersion times in aqueous solution of Au NPs. (c) Open-circuit voltage and (d) short-circuit current of gapless TENG devices based on flat PDMS (black), PDMS sponge (red), and PDMS/PDA/Au composites (blue) with immersion time = 24 h.

Fig. 5. (a) Output voltage (black), current (red), and power (blue) of the TENG with composite PDMS/PDA/Au sponge on the external load resistance. (b) Stability and durability test of the TENG under periodic contact-separation processes.