1. Schematic diagram of various composite films and devices for TENGs^{[20,21,22,23,24,25,26,27]}

2. Schematic diagram of rGONRs /PVDF based TENG, 3D-AFM image of the rGONRs/PVDF thin film, and output voltage of the rGONRs/PVDF based TENG for 500 cycles (a)^[20], schematic diagram of TiO₂/PDMS sponge based TENG, schematic of organic containment degradation by photocatalyst NPs in TiO₂/PDMS sponge (b)^[21], and SEM images of hierarchical structures for SiO₂/P(VDF-TrFE) composite fabricated by electrospinning process, and the surface potentials of pure P(VDF-TrFE) film (blue) and SiO₂/P(VDF-TrFE) composite film (red) (c)^[40] (Colorful figures are available on website)

3. Dielectric constants of the cellulose/ BaTiO₃ aerogel paper with different BaTiO₃ contents (the mass ratios of BaTiO₃ in C/BT-1, C/BT-3 and C/BT-5 were 50%, 75% and 83.3%, respectively) and schematic image of wireless application of the TENG(a)^[22], dielectric constants and charge densities of the BaTiO₃/PVDF nanocomposite films with different BaTiO₃ volume fractions (b)^[23], and SEM image of ZnSnO₃@PDMS composite film, and output currents and voltages of the corresponding TENGs with different ZnSnO₃ contents (c)^[24] (Colorful figures are available on website)

4. KPFM images (a) and power densities (b) of P(VDF-TrFE), PDMS, 30BTO and 30CCTO films^[46], electrical field distributions (finite-element simulation) (c) and power densities as a function of the external resistance (d) of the devices based on PDMS and PDMS@F-MOF^[49]

5. Internal resistances and output powers of PDMS@GPs composite membranes with different GP contents with inset showing structural schematic of corresponding TENG device (a)^[25], schematic image of PDMS@GO@SDS composite film and the output voltages of different TENGs (b)^[50], comparison of charge densities for TENGs : pure Nylon-11 and PVDF-TrFE (black), Nylon-11@MoS₂ and P(VDF-TrFE)@MoS₂ composite films in non-poled state (red) and poled state (blue) (c)^[51], comparison of charges for PVDF and PVDF/TOML nanocomposite films based TENGs with inset showing the picture of PVDF/TOML nanocomposite film (d)^[26], optical image of the CNF/phosphorene hybrid paper (e), and the comparison of voltages between pure CNF based TENG and CNF/ phosphorene hybrid paper based TENG (f)^[27]

6. Illustration of the fabrication process of a book-shaped TENG (a), normalized surface potential decay of PVDF/mSiO₂ nanofibers with different concentrations of mSiO₂ (b)^[55]; energy landscapes for (injected) charge carriers for SiO₂-FP before and during charging, and surface potential decays at elevated temperatures (c), electric field distributions during charging for two competing scenarios with injected charge residing at the aqueous-FP interface (I), and injected charge residing at the FP-oxide interface (II) (d)^[57]

Table 1. Fillers used in composite materials for TENGs