First-Principles Models of Triboelectrification

Triboelectrification has been known for millennia and remains of great practical importance, with applications spanning pharmaceuticals, electronics, industrial processes, and especially energy harvesting. Its inherent complexity, however, has long hindered a definitive understanding. In recent years, the advent of triboelectric nanogenerators (TENGs) has stimulated extensive experimental investigations and, in parallel, the development of promising first-principles-based theoretical models. Together, these advances have begun to clarify fundamental aspects of triboelectric charge transfer. This review traces the progression from early electron-transfer concepts to recent frameworks, including the backflow-stuck charges, thermoelectric, flexoelectric, and mechanochemical models. We discuss their evolution, the problems they address, the discoveries and insights they have enabled, as well as their limitations. At the beginning of the manuscript, special emphasis is given to the development of TENGs, which have both advanced practical applications and uncovered new triboelectric phenomena. Finally, we identify key open challenges and provide an outlook on future directions. The integration of complementary models through multiscale approaches, supported by systematic experimental validation, offers the most promising pathway toward a comprehensive understanding of this long-standing problem and the rational design of triboelectric materials and devices.