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

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

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

Interfacial engineering of high-curvature NiFe nanocone arrays for accelerated oxygen evolution via tip-induced electric field and rapid bubble detachment.

In gas-evolving electrocatalysis, the trade-off between mass transfer polarization and intrinsic activity remains a fundamental bottleneck. This work reports the interfacial engineering of high-curvature NiFe bimetallic nanocone arrays (NiFe-HC@NF) via a facile cathodic electrodeposition strategy. Finite element method (FEM) simulations reveal that the high-curvature tips trigger a strong localized electric field, which drives the directional migration and enrichment of OH- ions, thereby suppressing concentration polarization at the reaction interface. This physical enhancement is effectively integrated with the intrinsic Ni-Fe electronic synergistic effects, as verified by XPS, which optimize the surface electronic states for superior intrinsic kinetics. Furthermore, the unique 3D array configuration constructs a superhydrophilic and superaerophobic interface, ensuring ultrafast bubble detachment and maintaining effective active site exposure under vigorous gas-evolving conditions. As a result, the NiFe-HC@NF electrode delivers a low overpotential of 269.8 mV at 500 mA cm-2 and maintains remarkable structural and catalytic integrity for over 400 h at 100 mA cm-2. This study provides a compelling curvature-engineering strategy to break the mass-transport limitations in high-performance alkaline water electrolysis.

Potential of Zero Charge at Electrochemical Interfaces: Concepts, Measurement Strategies, and Emerging Applications

The potential of zero charge (PZC) is a key reference potential for understanding the electrochemical double layer at electrode/electrolyte interfaces. It describes the potential at which the excess charge on the electrode side becomes zero and provides a basis for discussing interfacial electric fields, ion distributions, solvent orientation, adsorption, and charge transfer reactions. Although the PZC can be defined clearly for liquid-metal electrodes that behave close to ideally polarizable interfaces, its assignment becomes more complex for solid electrodes because surface structure, oxide formation, hydrogen and oxygenated species adsorption, and specific adsorption can contribute to the measured response. This mini-review discusses classical and modern strategies for PZC determination, including electrocapillarity, differential capacitance, immersion measurements, CO displacement, piezoelectrochemical spectroscopy, scanning electrochemical cell microscopy, phase-sensitive in situ second harmonic generation, and atomic force microscopy approaches. By comparing their principles, applicable interfaces, and limitations, this mini-review emphasizes that PZC values should be interpreted together with the electrode material, electrolyte composition, surface state, local electronic structure, spatial scale, and measurement method.

Electrochemically Formed Submicrometer Liquid Metal Alloy Wires: A Route toward High-Surface-Area Electrochemical Electrodes

Electrochemical control of interfacial tension enables the extrusion of gallium-based liquid metals into high-surface-area nonspherical geometries relevant to electrocatalysis and hydrogen production. Here, liquid metal wires with diameters down to ∼500 nm are produced using quartz nanopipettes under moderate anodic polarization in an alkaline electrolyte. A morphology map identifies the operating window for continuous wire formation, distinct from droplet and blob regimes. The current response displays a previously unreported transient behavior, reaching three distinct maximum current density levels depending on the wire residence time. A model coupling the time-dependent liquid metal/electrolyte interfacial area with kinetic current density expressions accurately reproduces the transients and yields steady-state current densities, relaxation time constants, and an effective interfacial pseudocapacitance. Oxidation charge analysis reveals three distinct initial oxide growth rates, consistent with the characteristic residence time regimes, while kinetic analysis quantifies the corresponding oxide-induced overpotential losses. These results define a practical lower size limit of ∼500 nm for electrochemical liquid metal wire fabrication and establish a quantitative framework for their use in high-surface-area electrochemical reactors.

Experimental study on hydrogen bubble growth and detachment on surface-modified electrodes

Wide-Field Opto-Iontronic iSCAT Mapping of Interfacial Charging and Electrical Connectivity

Spatial variations in electrical connectivity and interfacial ion accumulation can strongly influence electrochemical performance, yet these properties are difficult to visualize directly with conventional ensemble measurements. Here, we introduce potential-modulated opto-iontronic microscopy, an interferometric scattering microscopy (iSCAT) approach for wide-field imaging of electric-double-layer (EDL) dynamics at nanostructured electrodes. Sinusoidal potentials were applied to focused-ion-beam-fabricated indium tin oxide (ITO) nanoholes, and the optical response was extracted at the modulation frequency by Fourier demodulation. The optical modulation amplitude increased approximately linearly with modulation voltage above a low-voltage roll-off and decreased with increasing frequency, consistent with kinetically limited interfacial charging. We then mapped the potential-synchronized optical amplitude across patterned ITO electrodes. Electrically isolated blocks exhibited strongly suppressed modulation signals, whereas electrically connected and partially milled nanogrid structures showed pronounced responses. These results demonstrate label-free optical mapping of local charging dynamics and electrical connectivity at heterogeneous electrochemical interfaces using a commercially available iSCAT platform.