From parasitic voids to reactive phases: gas bubbles as electrified microreactors

Gas bubbles in aqueous reactors are usually treated as liabilities; they mask active surfaces, disturb transport, and lower energy efficiency. Recent studies have begun to overturn this view. Curved gas-liquid interfaces can behave as electrified microreactors. Here, electrified is used broadly to include interfaces charged by external polarization, spontaneous interfacial charging, or contact electrification. Their charge accumulation, asymmetric solvation, and local electric fields have been linked to altered ion activities, apparent redox potentials, and reaction pathways that are otherwise unfavorable in bulk water. Bubble chemistry has been reported in hydrogen peroxide generation, pollutant removal, nitrogen fixation, methane oxidation, and carbon dioxide reduction, often without an added conventional catalyst or with low-material-input conditions. This review organizes these developments into four regimes: pinned bubble coronas at biased solids, dispersed micro- and nano-bubbles in bulk water, curvature-amplified gas-liquid interfaces, and bubble-mediated carbon and nitrogen transformations. The outstanding challenge is no longer whether bubbles are reactive, but how interfacial electric fields, ion gradients, confined liquid films, and radical pathways can be measured, separated, and scaled without losing selectivity. The emerging design principle is to engineer bubbles as reaction phases, rather than treating them merely as losses. Coupling bubble interfaces with electrochemical, photochemical, and contact-electrification strategies may turn them into controllable elements of sustainable chemistry.