Fig. 1: Surface-adherent gas bubbles increase electrochemical current outputs.

a Normalized amperometric curves acquired in aqueous 0.1 M sodium hydroxide using an ITO electrode, biased at +1.2 V vs. SHE, in the presence of surface-adherent oxygen cavities. The current density recorded in the presence of surface-adherent bubbles (J) is systematically higher than that found in the absence of bubbles (J₀). The experimental J/J₀ ratio scales with the total bubble corona length (C, data analysis in Supplementary Fig. 2, and Supplementary Table 1). b Optical images of the ITO electrode acquired during the current measurements reported in (a). Scale bars are 2 mm. Wide-field views of the entire electrode area are in Supplementary Fig. 2. c Representative bright-field image (side view) of an oxygen bubble on the ITO electrode. The scale bar is 200 µm. d Schematics of the electrochemical generation, and fluorescence detection, of HO^• in the corona of an electrode-adherent bubble. e, f Epifluorescence microscopy images for the detection of HO^• around an argon bubble adhering on an ITO electrode. The electrode is immersed in an aqueous solution of sodium hydroxide (0.1 M) and 3ʹ-(p-hydroxyphenyl) fluorescein (10 µM), and it is either rested at its open-circuit potential (e OCP), or biased at +1.2 V vs. SHE (f). See also Supplementary Video 1. g, h Confocal microscopy images for the HO^• detection around nitrogen bubbles supported on a biased (+1.2 V vs. SHE) ITO slide. The aqueous electrolyte contains dichlorodihydrofluorescein diacetate (100 µM) and sodium hydroxide (0.1 M). The z height above the electrode surface is specified in the figure. Scale bars in e–h are 200 µm. Emission intensities for the images (frames) in e–h are normalized to the highest-intensity value measured in each frame. i Fluorescence emission intensity profiles measured along the dashed lines of panels g, h, showing a larger emission at the gas–liquid interface closer to the electrode surface.