Kinetic Modulation of Outer-Sphere Electron Transfer Reactions on Graphene Electrode with a Sub-surface Metal Substrate

Abstract

The atomic thickness of graphene electrodes makes them a suitable platform to explore interfacial interactions with dissimilar materials and their impact on the rates and mechanisms of electrochemical reactions. Here, we report on the modulation of the electrochemical kinetics of outer-sphere redox mediators by metal electrodes buried in the sub-surface of continuous double layer graphene electrodes. Graphene was obtained via chemical vapor deposition and a near-full coverage of graphene over the metal surface was inspected via microscopy and by the use of electrochemically active surface redox probes. Enhancements in the rate of electron transfer on three reactive species, ferrocyanide, ferricyanide, and ferrocene, were observed on graphene coated metal deposits using scanning electrochemical microscopy in the feedback mode. Our results strongly suggest that the electron transfer kinetics to outer sphere redox species across the graphene/electrolyte interface is significantly enhanced by the use of subsurface metals. We show that buried Au deposits exhibit ca. 5 times enhancement of the electrochemical rate constant. These enhancements are likely a consequence of increased electronic density of states due to a donating effect from the substrate.