LAUSR

DOI: 10.1002/aenm.202000965 environment as the energy of a new era.[1–4] Among various kinds of distributed energy, ambient mechanical energy provides a promising power source because of its wide distribution and sufficient availability. With desirable merits of simple structure, light weight, broad material availability, low cost, and high efficiency even at low-frequency operation, the triboelectric nanogenerators (TENGs) have been proved as an alternative technology for extracting ambient mechanical energy that is ubiquitous and almost endless.[5–8] Based on the coupling effect of triboelectrification and electrostatic induction, the conventional TENG, called AC-TENG here due to its alternating current (AC) output character, can convert mechanical energy into electrical energy, which have exhibited great potential to operate as self-charging power system[9–14] and self-powered sensors.[15–19] As an energy generator, the extensive application of TENG highly depends on its output power density and energy conversion efficiency, which are dictated by the triboelectric charge density quadratically. Recently, a great deal of research has been focused on materials selection,[20,21] surface modification,[22] environment optimization,[23–25] structure design,[26–28] and ultrathin dielectric layer utilization[29,30] to enhance the triboelectric charges. Nevertheless, the electrostatic breakdown effect in ambition environment can inevitably reduce the triboelectric charges, causing the loss of the electrostatic energy.[31] On the other hand, the maximal surface charge density can be achieved after several cycles through charge accumulation process.[32] Therefore, the following triboelectrification process is invalid for charge accumulation, which will further reduce the energy conversion efficiency. Currently, direct current triboelectric nanogenerators (DC-TENGs), based on the conjunction of triboelectrification and electrostatic breakdown, have been developed for directly converting mechanical energy to a constant current.[33–35] Compared to traditional TENGs obtain a DC output based on electrostatic induction by using a full-wave rectifier, rotary rectifier bridge,[36] or a multi-phase rotation-type structure,[37] DC-TENG can supply a constant current power source to directly power electronics without any rectifier or energy storage devices, which can serve as a promising solution to miniaturize the selfpowered systems for the era of distributed electronic devices. With the advantages of its light weight, low cost, and high efficiency especially at low operation frequency, the triboelectric nanogenerator (TENG) is considered to be a potential solution for self-powered sensor networks and large-scale renewable blue energy. However, the conventional TENG converts mechanical energy into electrical energy only via either electrostatic induction or electrostatic breakdown. Here, a novel dual-mode TENG is presented, which can simultaneously harvest mechanical energy by electrostatic induction and dielectric breakdown in a single device. Based on the complementary working mechanism, it achieves a great improvement in the output performance with the sum of two TENGs via a single mechanism and reveals the effect of dielectric layer thickness on the triboelectrification, electrostatic induction, and air breakdown. This study establishes a new methodology to optimize TENGs and provides a new tool to investigate the triboelectrification, electrostatic induction and dielectric breakdown simultaneously.