3D-Printing TENGs made into the insole. (a) Schematic diagram of the fabrication of the 3DP-TENGs and the hierarchical porous structure. (b) The images of top view and side view (insets) of a 3DP-TENG insole. (c) Working principles of a single pore. (d) The comparison of output performance of the 3DP-TENGs and the traditional TNEGs. (e) Voltage feature of a 3DP-TENG insole charged 22 μ
F capacitor which is powering the electronic watch. Image of the self-charging system to power electronic watch (inset). (f) Photograph of a 3DP-TENG insole simultaneously lighting LEDs of a self-powered lighting shoe inside (top). Reproduced with permission from [167
]. Copyright Wiley-VCH, 2018.