In Situ Fluorescence Imaging of Electrode‐Structure‐Dependent Dissolved Oxygen Distributions During Electrocatalytic H 2 O 2 Production

ABSTRACT Hydrogen peroxide (H 2 O 2 ) 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, H 2 O 2 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 H 2 O 2 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 H 2 O 2 electrosynthesis.