TENGs embedded in the insoles. (a) The structure of a multilayered TENG with two different viewing angles and SEM image of nanopores created on the Al foil surface. The scale bar is 200 nm. (b) Photograph of the inner structure of the insole, showing another TENG enclosed at the rear section of the insole. The scale bar is 2 cm. (c) Open-circuit voltage of the TENG. (d) Photograph of the self-lighting shoe during normal walking, showing lighted LED bulbs in the air cushion. Reproduced with permission from [163
]. Copyright Elsevier, 2013. (e) Structure design of the NM-TENG. (f) Open-circuit voltage of the NM-TENG driven by human hand tapping. (g) Optical image of NM-TENG embedded in the insole. (h) The NM-TENG based power generating insole could efficiently harvest energy from human walking and light up about 400 LEDs. Reproduced with permission from [130
]. Copyright Elsevier, 2017.