Imaging Electrode Heterogeneity Using Chemically Confined Fluorescence Electrochemical Microscopy

Abstract

By varying the total and the relative concentrations of a strong acid (HClO) and a pH-sensitive fluorescent dye (8-hydroxypyrene-1,3,6-trisulfonate), this work demonstrates that both the hydrogen evolution reaction or the oxygen reduction reaction can be selectively and optically studied at an electrochemical interface. The local pH shift driven by the redox reaction can be visualized through fluorescence imaging of the interface. The use of finite strong acid concentrations further serves to constrain the pH change to a thin layer adjacent to the surface. This chemical confinement of the fluorophore improves the system's resolution and enables micrometer scale heterogeneity on the electrode surface to be readily visualized.

In Situ Fluorescence Tomography Enables a 3D Mapping of Enzymatic O2 Reduction at the Electrochemical Interface

“…The repartition of fluorescence and therefore of protons in the volume of the electrolyte solution in the vicinity of the electrode surface can be visualized, revealing the proton gradient direction from the electrode surface towards the bulk electrolyte. As expected, the expansion of the diffusion layer drastically decreases with increasing buffer concentrations, 29 being almost undetectable at concentrations higher than 50 mM buffer. The shape and dimensions of the diffusion layer can also be characterized.…”

“…One possibility is to image the plane perpendicular to the electrode surface. [29][30][31] Another possibility is to rebuild 3D profiles thanks to fluorescence confocal laser scanning microscopy (FCLSM). In FCLSM, the photons emitted are collected from an optical "slice" that corresponds to a thin volume with a narrow field depth at a given focal plane.…”

In‐Operando Mapping of pH Distribution in Electrochemical Processes

“…Numerous fluorescent probes have been reported for the detection of pH . In this study, in‐operando visualization of the pH distribution was performed using a combination of two fluorescent pH‐sensitive dyes: LysoSensor Green DND‐189 (LSG, p K a ≈5.2) and 5(6)‐carboxynaphthofluorescein (CNF, p K a ≈7.6), to cover a wide pH range.…”

Spatially resolved electrochemiluminescence through a chemical lens

“…The chemical connement of H + can in principle be controlled by the buffer capacity of the supporting electrolyte. 39,40 The overall effect will result in the modulation of the concentration proles of both TPrA radicals, i.e., change of the ECL-active region. Indeed, the spatial distribution of ECL is the luminescent signature of the concentration proles of both diffusing TPrA radicals, which react with the immobilized [Ru(bpy) 3 ] 2+ and thus control the extension of the ECL-emitting layer.…”