Moiré-Based Topological Defects for Tunable Electrochemistry

Interfacial electron-transfer reactions underpin the interconversion of electrical and chemical energy. At electrode–electrolyte interfaces, atomic defects like vacancies and step edges are frequently implicated as active sites that mediate reactivity by introducing high densities of localized electronic states. However, these sites are challenging to deterministically synthesize and control at an atomic level. Moiré superlattices of atomically thin layers generate flat electronic bands and associated localized states that are precisely tunable by the interlayer twist angle. Here we show systematic, >80-fold control over the interfacial electron-transfer rate constant by controlling the stacking configuration and moiré angles in few-layer graphene. At small angles of twisted graphene, the kinetic modulation is governed by well-defined `topological' defects of the moiré superlattice, consisting of atomic configurations that cannot be realized independently of the moiré. These topological defects mediate outer-sphere electrochemical reactions with rates comparable to bulk metals, notwithstanding their consisting of only three atomic layers. Moiré superlattices therefore serve as an unparalleled platform for systematically interrogating and exploiting the dependence of electron-transfer rates on electronic structure.