In Situ Fluorescence Imaging of Electrode-Structure-Dependent Dissolved Oxygen Distributions During Electrocatalytic...

Hydrogen peroxide (H₂O₂) is an important green oxidant, and its electrosynthesis via the two-electron oxygen reduction reaction (2e^- ORR) provides a sustainable alternative to the conventional anthraquinone process. However, H₂O₂ production is governed not only by catalyst properties but also by the local dissolved oxygen (DO) distribution at the electrode-electrolyte interface, which remains difficult to resolve using conventional bulk measurements. Herein, we develop an in situ fluorescence imaging system based on the oxygen-dependent quenching of tris(2,2-bipyridine) ruthenium(II) (Ru(bpy)₃ ²⁺), enabling quantitative visualization of fluorescence-derived DO variations in the near-electrode region during electrocatalytic H₂O₂ production. A reliable calibration correlates fluorescence intensity with DO concentration, while a DnCNN-based denoising strategy suppresses fluorescence noise, improves the detection limit, and preserves pixel-scale spatial information. Using this system, current-dependent near-interface fluorescence-derived DO variation is monitored, revealing rapid initial DO redistribution followed by a quasi-steady transport-reaction balance. Comparative studies of carbon paper and gas diffusion electrodes reveal distinct electrode-architecture-associated near-interface DO responses, suggesting differences in local oxygen accessibility and interfacial transport behavior. Spatially resolved analysis of laser-perforated porous electrodes reveals heterogeneous DO distributions in non-pore regions, pore interiors, and pore edges. This work provides a quantitative in situ approach for probing electrode-structure-dependent DO distributions during H₂O₂ electrosynthesis.