Measurements of Interfacial Electric Fields at Graphene-Modified Electrode Surfaces During High Current Density Operation
Understanding electric fields at electrochemical interfaces is essential for optimizing electrocatalytic processes. However, their measurement under high current densities is limited by gas evolution, which obstructs access to the electrode surface. To address this, we developed a custom flow cell featuring an internal nozzle that directs fluid across the electrode surface. This high-velocity flow suppresses bubble nucleation by limiting local hydrogen supersaturation and thereby preserves optical access to the electrode. This design enables in situ Raman spectroscopy and direct quantification of interfacial electric fields under current densities relevant to electrolysis. High-speed optical imaging shows that bubble coverage decreases by 85–88% at 100 mL min⁻¹ relative to stagnant conditions. With this improvement, stable Raman measurements are possible at current densities up to 25 mA cm⁻², which is more than two orders of magnitude higher than in a non-flowing cell. Under these conditions, graphene-encapsulated Pt and Au electrodes exhibit Stark shifts in the graphene G-band. These shifts allow extraction of charge-carrier densities and local interfacial fields up to 3.8 × 10⁶ V cm⁻¹. Differences between graphene/Pt and graphene/Au highlight the substrate-dependent nature of the doping behavior. We propose a framework in which metal work function, proton adsorption, and electrostatic gating collectively determine the potential-dependent graphene doping and the resulting interfacial electric field.