Fig. 4: Deciphering the mechanism of H₂O₂ generation in the MPR–water system.

A Illustration of isotope labeling of H₂O₂-promoted deborylation of 4-carboxyphenylboronic acid into 4-hydroxybenzoic acid. B High-resolution mass spectrometric analysis of 4-hydroxybenzoic acid products produced under O₂/H₂O, O₂/H₂¹⁸O, and ¹⁸O₂/H₂O conditions. C Effects of electron scavenger p-benzoquinone (PBQ) on H₂O₂ generation rate of XAD-1180N at normal (aerobic) conditions. D Confirmation of superoxide radical anions (·O₂⁻) through the use of superoxide dismutase (SOD) and its inhibitor N, N-diethyldithiocarbamate (DDC). E Comparison of H₂O₂ generation rates of XAD-1180N at different pH values in 100 mM phosphate buffer solution. DIW represents deionized water. F ESR trapping of hydroxyl radicals (·OH). G Quantification of time-evolved formation of ·OH radicals during the generation of H₂O₂, measured using terephthalic acid (TA) as a probe. H H₂O₂ Evolution in the presence of ·OH radical scavenger isopropanol (IPA) at varying concentrations. I Proposed pathway of H₂O₂ generation in the MPR–water system, involving interfacial charge separation, electron transfer, and formation of immediate species. ORR dominates H₂O₂ formation, while the source of electrons remains unresolved. Two possible electron-donation pathways at aqueous micro-interfaces are proposed: sole oxidation of the solid surface (path A) and oxidation of water (path B). Data in (D, E, H) are presented as mean ± standard deviation (n = 3 independent experiments).