In Situ Measurements of Interfacial Electric Fields at Graphene-Modified Electrode Surfaces During High Current Density Operation

Abstract

Understanding electric fields at electrode/electrolyte interfaces strongly influences electrocatalytic processes, yet their characterization at high current densities is often hindered by gas evolution that interferes with physical and electromagnetic probes. Herein, a custom electrochemical flow cell is presented that suppresses bubble nucleation by directing a high-velocity jet of electrolyte toward the electrode surface through an internal nozzle. This enables in situ Raman spectroscopy and determination of electric field strengths at electrode/electrolyte interfaces under elevated current densities relevant to electrolysis and fuel cell applications. Video analysis shows that electrolyte flow reduces hydrogen bubble coverage on platinum (Pt) thin-film electrodes by85–88%. This enables stable Raman measurements at current densities up to 25 mA cm⁻², nearly two orders of magnitude higher than in a stagnant cell. Under reduced bubble coverage, graphene supported on Pt and gold (Au) electrodes exhibits Stark shifts in the graphene G-band corresponding to electric field strengths up to 10⁶ V cm⁻¹. The measurements reveal substrate-dependent behavior, including a ≈0.4 V shift in the graphene charge-neutrality point for Graphene/Pt relative to Graphene/Au. We propose a framework in which substrate work function, proton adsorption, and electrostatic gating collectively govern potential-dependent graphene doping and interfacial electric field strength at the electrode/electrolyte interface