Transient physical modeling and comprehensive optimal design of air-breakdown direct-current triboelectric nanogenerators

Direct-Current Triboelectric Nanogenerators (DC-TENGs) achieves an direct-current (DC) output instead of traditional alternating-current (AC) output of TENG. Among the various structure designs of DC-TENGs, the air-breakdown DC-TENG has created a record of energy density and an almost constant-current output, which has great potential in practical applications. This paper proposes a transient physical-field model and carries out comprehensive optimal design for air-breakdown DC-TENG. The beneficial breakdown domain (BBD) and harmful breakdown domain (HBD) are introduced to reveal the dynamic mechanism that distinguishes the DC-TENGs from AC-TENGs. Indexes of the breakdown charge ratio (BCR) and leading charge density (LCD) are defined to evaluate the extent to which the high-density surface charge is effectively exploited in electricity generation based on the beneficial breakdown effect. The output characteristics of air-breakdown DC-TENGs are theoretically analyzed, revealing the influence of the load resistance, device structure parameters, and initial charge density. Therefore, the optimal design of air-breakdown DC-TENGs is carried out with a high output power and low matching resistance. Finally, these superior performances are verified by experiments, so that the proposed transient physical model and comprehensive optimization method can be reliably extended to the design of all types of air-breakdown DC-TENG, and promote its application in a wide range of fields.