Spontaneous Galvanic Electron Injection for Programmable Functionalization and Patterning of Monolayer Graphene

Achieving high-dose, spatially programmable covalent functionalization of monolayer graphene has so far relied on externally powered activation─imposed electrochemical bias, highly reducing alkali metals, or laser/plasma inputs─approaches that are often aggressive and tie chemical dose to hardware-defined fields, limiting orthogonal control. Here, we introduce galvanic electron injection (GEI), a self-powered strategy that leverages the spontaneous interfacial potential at a metal-graphene junction to achieve programmable covalent functionalization under ambient conditions. The process is governed by a predictive "metal/reagent potential" matching rule: metals such as Ag, Cu, and Mg readily activate graphene for C-C bond formation with aryl diazonium salts within one second (Raman I_D/I_G up to ≈3). The same framework extends to more challenging alkyl iodides through minimal external compensation or by using stronger reductants (Na, K). Chemical dose is orthogonally programmed by metal/reagent choice (thermodynamics), reaction time (kinetics), and oxygen content. Notably, oxygen tunes grafting density from an I_D/I_G of ∼0.5 (at 0% O₂) to ∼3.0 (at 20% O₂) via an oxygen-assisted injection mechanism. Integrating GEI with photolithography converts metal features into dual-role "mask-plus-injectors", enabling self-aligned chemical writing with ∼1 μm resolution. These results demonstrate that GEI enables contact-mediated, spatially controlled graphene functionalization under mild conditions.