Effects of Graphene Redox on Its Triboelectrification at the Nanoscale

Controlling triboelectrification behaviors of graphene-based materials plays a key role in the output performance and reliability of the graphene-based triboelectric nanogenerators. The electrical and mechanical properties of graphene-based materials are sensitive to their redox, and the study of the redox effects on their triboelectrification at nanoscale is the basis for regulating the triboelectrification performance. Here, the triboelectrification behaviors of graphene oxide (GO) and thermally and chemically reduced graphene oxide (RGO) were explored by scanning probe microscopy. It is found that the triboelectric charges on GO are localized in the rubbed region due to the sp3 hybridized structure. However, on RGO, triboelectric charges are distributed over the whole sheet due to the restored sp2 structure. In the rubbing process with insufficient contact, wrinkles in RGO, contact forces, and friction modes affect the triboelectric charging process dramatically. These influences are related to the resistance threshold of nanoscale tip-sample contact that is related to the present tip-sample potential difference, the contact force, the roughness, and the friction mode. When the tip-sample contact is sufficient enough, the charge transfer in the triboelectric charging process can reach equilibrium, and the roughness, contact force, and rubbing mode have no effect on the triboelectrification. Moreover, the triboelectric potential is linearly dependent on the initial potential, lifting (positive) with a negative initial potential and dropping (negative) with a positive initial potential. Tunneling triboelectrification on RGO is also affected by the initial potential, presenting a localized distribution of triboelectric charges in the rubbed area. Our findings would provide guidance for regulating the triboelectric charges on graphene-based materials and designing high-performance graphene-based triboelectric nanogenerators.

Automated summary

Controlling the behavior of graphene-based materials in triboelectrification is crucial for optimizing output performance and reliability of graphene-based triboelectric nanogenerators. This study investigated the triboelectrification behaviors of graphene oxide (GO) and thermally and chemically reduced graphene oxide (RGO) using scanning probe microscopy. The results revealed that the distribution of triboelectric charges on GO is localized due to its sp3 hybridized structure, while on RGO, the charges are distributed over the entire sheet because of the restored sp2 structure. Factors such as wrinkles, contact forces, and friction modes in the rubbing process had a significant influence on the triboelectric charging process of RGO. Additionally, the triboelectric potential was found to be linearly dependent on the initial potential, and tunneling triboelectrification on RGO exhibited a localized distribution of charges. These findings provide valuable insights for regulating triboelectric charges on graphene-based materials and designing high-performance graphene-based triboelectric nanogenerators.