Contact Electrification via Redox-Active Molecules.

Contact electrification, as the transfer of charge upon the contact of two (dis)similar materials, is strongly influenced by surface chemistry, which governs the efficiency of charge separation. For harvesting electrical energy from mechanical energy, material pairs with high electron-transfer efficiency are essential. Here, we introduce a strategy to use electronic charge transfer in contact electrification via surface functionalization with redox-active organic molecules. Specifically, we functionalize Au(111) surfaces with mercaptomethyl-terminated redox-active molecules, namely triphenylamine and tetrathiafulvalene as donors and 11,11,12,12-tetracyano-9,10-anthraquinodimethane as an acceptor, achieving stable and covalent immobilization, as confirmed by X-ray photoelectron spectroscopy, electrochemical characterization, and density functional theory calculations, and enabling molecular-level electron-transfer. To quantify charge transfer at the micrometer scale, we introduce a contact electrification assay combining atomic force microscopy-based force spectroscopy and Kelvin probe force microscopy. This approach allows for a precise measurement of charge transfer between Au(111) surfaces functionalized with redox-active molecules, revealing an electron-driven mechanism capable of achieving surface charge densities of (120 ± 17) µC m-2. Our findings deepen the fundamental understanding of contact electrification by demonstrating that electron transfer-depending on the choice of materials-can indeed be its origin, and pave the way for the development of more efficient triboelectric devices.