Solvent-assisted running-in strategy enables improved triboelectric nanogenerator output

The challenge of low electric outputs of triboelectric nanogenerators limits their large-scale practical applications. Although considerable efforts have been focused on improving the output, e.g., enhancing the surface charge densities of tribo-materials, the improvements are either too weak or too complicated. Here, we show that optimizing the running-in process with dimethyl sulfoxide solvent can increase the charge density of polyimide-based triboelectric nanogenerators to 2.5 mC m^-2, a fourfold enhancement compared with untreated devices. The solvent-assisted running-in process removes the worn radicals, debris, or transferred materials on the contact surface, reducing electron transfer hindrance issues. Through time-of-flight secondary ion mass spectrometry, molecular dynamics simulations and density functional theory analyses at the molecular and electronic levels, the results indicate that running-in friction further induces the breakage of the N-C bonds in polyimide, resulting in the freedom to release amide groups. Together with the function of dimethyl sulfoxide-driven extraction, the amide-containing chains rearrange into "molecular brushes" towards contact surfaces, among which the highly electron-withdrawing C = O bonds are thus exposed and capture electrons from the counter tribolayer. This solvent-assisted running-in strategy improves electrical output in engineering polymers without material modification and clarifies how tribological running-in can be used to regulate triboelectric performances.