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Density of Surface States: Another Key Contributing Factor in Triboelectric Charge Generation.

The triboelectric nanogenerator (TENG) has been invented as a technology for harvesting mechanical energy, as well as for allocating quantized charge for scientific instruments. The charge generation of the TENG is mainly related to the triboelectric effect or contact electrification (CE) as usually described by the potential-well-electron-cloud model, while the triboelectric charge transfer is related to the difference in the occupied energy levels of electrons. However, in our experiment, we observed an abnormal triboelectric charge generation phenomena between ternary materials, which cannot be explained by the occupied energy level difference only. To address this issue, we proposed the model based on the density of surface states (DOSS) as another key contributing factor to the triboelectric charge generation. To demonstrate our model, we introduced an approach to measure the DOSS through applying external electric field between two triboelectric surfaces. Our experiments confirmed the contribution of the DOSS to the triboelectric charge generation, with the derived charge density consistent with the measured results, which verified our model. We also predicted that the FEP has the potential to achieve a high charge density of ∼5.6 × 10-4 C/m2, which is close to the reported maximum values. This study provides another key contributing factor to the triboelectric charge generation, which may provide a more complete model for guiding the material selection and modification to tailor the surface charge generated by the CE.