Fig. 1. Schematic diagram of wearable energy system based on triboelectric nanogenerator^[40-48].

Fig. 2. The four fundamental modes of the TENG and the mechanisms of contact electrification: (a) The four fundamental modes of the TENG^[49]; the overlapped electron-cloud model proposed for explaining contact electrification (b) between solid and solid state^[20], (c) between solid and liquid state^[50].

Fig. 3. Influence of molecular structure of polymer materials on triboelectrification: (a) Schematic diagram of ion irradiation and contact electrification of polymer materials^[60]; (b) the main chain is same, the electron cloud range of different groups in the side chain^[61].

Fig. 4. Textile-based indirectly wearable TENG: (a) 3D double-faced interlock fabric TENG for bio-motion energy harvesting^[43]; (b) direct current fabric TENG for biomotion energy harvesting^[65]; (c) 3D orthogonal woven TENG^[66].

Fig. 5. Thin film-based indirectly wearable TENG: (a) An ultrathin flexible single-electrode TENG^[67]; (b) wearable triboelectric generator^[68]; (c) gas-permeable on-skin TENG^[69]; (d) TENG with ultrathin thickness^[70].

Fig. 6. Elastomer-based indirectly wearable TENG: (a) Stretchable and waterproof TENG ^[45]; (b) self-charging power package^[71]; (c) a bionic stretchable nanogenerator^[72]; (d) fully elastic TENG^[73].

Fig. 7. Wearable TENG with special structure: (a) Wearable pouch-type TENG^[74]; (b) TENG weaved into a coat and assembled under shoes^[75]; (c) TENG enabled body sensor network^[47].

Fig. 8. Textile-based directly wearable TENG: (a) A highly stretchable and washable all-yarn based self-charging knitting power textile^[76]; (b) skin-touch-actuated textile-based triboelectric nanogenerator^[77]; (c) single-thread-based TENG^[78]; (d) flexible single-strand fiber-based woven structured triboelectric nanogenerator^[79].

Fig. 9. Thin film-based directly wearable TENG: (a) Flexible and stretchable TENG^[80]; (b) crumpled nanofibrous membranes based TENG^[81]; (c) a flexible, lightweight TENG^[82]; (d) a breathable and antibacterial TENG^[83].

Fig. 10. Elastomer-based directly wearable TENG: (a) Ultrastretchable, transparent TENG^[84]; (b) electric eel-skin-inspired TENG^[44]; (c) a liquid PEDOT:PSS electrode-based stretchable TENG^[85].

Fig. 11. Directly wearable TENG with special structure: (a) A highly shape-adaptive TENG based on conductive liquid^[48]; (b) an airtight-cavity-structural triboelectric nanogenerator^[86].

Fig. 12. Advances in power management circuits: (a) Self-charging power systems; (b) effective energy storage from a triboelectric nanogenerator^[41]; (c) a universal self-charging system^[40]; (d) universal power management strategy^[12]; (e) switched-capacitor-convertors for output power management^[87].