fig4

Figure 4. The evolution of the energy harvesting mechanism in the H-TENG. (A₁ and A₂) Schematic diagrams and corresponding electric potential/field distributions illustrating the two operational phases: (A₁) The initial contact electrification phase, where charge transfer occurs upon physical contact between the droplet and the friction layer. (A₂) The mature electret-driven polarization phase, where the persistent electric field from the charged friction layer polarizes the droplet (A₃ and A₄); (B and C) High-speed imaging and corresponding current output capture droplet-electrode interaction dynamics and transient current signatures. H-TENG: Hemispherical triboelectric nanogenerator.