Journal Article triboelectric nanogenerators charge excitation energy harvesting triboelectric nanogenerator Review air breakdown charge density charge generation charge hopping charge lock‐free strategy charge loss mechanisms charge self‐injection charge trapping durability dynamic charge transport electroosmosis energy density high output charge density high-voltage sources high‐output performance intelligent monitoring interfacial electrical energy extraction liquid suspension micro-flow pumps mode switching motion control non-contact quasi‐dipole potential relative permittivity