During alkaline water electrolysis, gas-evolving reactions generate bubbles that contribute to ohmic losses and an increase in activation and concentration overpotentials affect cell efficiency. Building on prior studies of bubble behavior, this work introduces two new aspects: spatially resolved void fraction near the electrode surface and locally generated gas volume flow as an indicator of surface activity. Both quantities are correlated with measured bubble dynamics. To achieve this, the oxygen evolution reaction is studied on a vertical wire electrode using Laser-Marked Shadowgraphy over a wide current-density range and multiple heights. Statistical distributions of bubble position, size, and velocity are obtained, together with local void fraction and gas volume flow. Their dependence on current density and vertical position is analyzed. Results show that bubble size primarily governs void fraction and, thus, bubble-induced resistance. A feedback mechanism is observed in which bubble-induced electrolyte flow enhances bubble transport, while bubble–bubble interactions cause a slowdown at high current densities. Spatial variations in generated gas volume flow reveal inhomogeneous apparent surface activity linked to convective transport. Overall, the results demonstrate the interplay of bubble dynamics and the electrochemical process and underscore the need for quantitative, spatially resolved, and statistically converged data for bubble dynamics. • Spatially resolved measurement of void fraction for different current densities. • Local measurement of apparent generated volume flow. • Indirect observation of inhomogeneity of surface activity. • Linking surface activity to bubble dynamics.
Franz et al. (Wed,) studied this question.