Alcohol-Regulated H₂O₂ Formation in O₂-Containing Gas–Liquid Discharge Plasma

Hydrogen peroxide formation in gas–liquid discharge plasma is usually associated with the recombination of plasma-generated hydroxyl radicals (•OH). Although alcohols are commonly regarded as •OH scavengers and are therefore expected to inhibit peroxide formation, their effects in plasma–liquid environments remain poorly understood. Here, methanol was used as a model alcohol to study alcohol-regulated H₂O₂ formation in an O₂-containing bubble plasma system. Low methanol volume fractions markedly enhanced H₂O₂ accumulation, whereas excessive methanol caused early saturation and reduced sustained peroxide production. H₂O₂ formation also showed a non-monotonic dependence on O₂ fraction, indicating the need to balance methanol content and O₂ availability. OES, electron-density analysis, and ESR measurements revealed that alcohols regulate plasma-induced H₂O₂ formation by coupling plasma excitation with liquid-phase radical chemistry, rather than simply acting as hydroxyl radical scavengers.