Fig. 2: The electric double layer of a bubble in ultrapure water.

a Simplified schematics of the gas–liquid interface of a bubble, depicting an unbalanced excess of OH⁻ ions. b Quantum-chemically computed redox potential for the HO^•/OH⁻ couple as a function of the OH⁻ concentration, as calculated by considering electrostatic repulsions between OH⁻ (symbols), together with the tabled experimental¹³ potential corresponding to standard conditions of 1 M (dashed line). Details on the calculations are in Supplementary Note 1. c Selected time-stamped timeframes obtained from bright-field microscopy imaging experiments (Supplementary Video 2), tracking the position of an oxygen bubble accelerating in ultrapure water toward the anode under an electric field of ca. 40 V cm⁻¹. Scale bars are 500 µm. d Photographs taken prior (left) and after (right) the formation of a fine gas–water emulsion obtained by generating a high quantity of nitrogen microbubbles (9.3 × 10⁷ L⁻¹, average bubble diameter is 50 µm), see Supplementary Note 3. e Representative pH drop induced by the formation of a gas emulsion in water.