The global climate crisis and rising greenhouse gas emissions highlight the urgent need to shift from fossil fuels to sustainable energy solutions. Hydrogen is increasingly recognized as a crucial tool for decarbonization, with significant potential to drive the transition to clean energy. This study examines hydrogen production via water electrolysis, focusing on forced-flow alkaline water electrolysers (AWE). It investigates how factors such as current density (j), height above the electrode (z), and superficial liquid velocity (w_l) influence velocity profiles, turbulence, and bubble dynamics within the electrolyser.

The results demonstrate that variations in current density j and height z strongly affect the velocity profile w(x), with higher values promoting buoyancy-driven flows and accelerating the liquid, especially near the electrode where gas flux is highest. These effects are more pronounced on the hydrogen (H2) side, where increased gas production generates larger velocities and broader plume dispersion. In contrast, higher superficial liquid velocity w_l shifts the flow regime toward forced convection, attenuating bubble plume effects and reducing the contrast between plume and bulk flow.

Turbulence intensity I(x) also depends on j, z, and w_l, increasing with higher j or z due to intensified bubble interactions and buoyancy effects, particularly near the hydrogen electrode. However, increased w_l reduces turbulence in buoyancy-dominated regions by structuring the plume. The model aligns well with experimental data, especially when fitting velocity profiles to a step-function regime for natural convection, achieving scaling exponents consistent with theoretical predictions.

This study identifies the Richardson number (Ri) as a valuable dimensionless measure of convection type, with a transition from natural to mixed convection observed around Ri = 1. Ri unifies the effects of j, z, and w_l on velocity distribution, offering enhanced design flexibility for electrolysers. Bubble-induced turbulence and wakes caused by large bubbles are the primary drivers of dispersion within the electrolyser, accounting for over 98% of total observed dispersion. This finding underscores the dominant role of turbulent dispersion over hydrodynamic or shear-induced effects in this forced-flow system.

Detached bubbles significantly enhance liquid and gas flow through buoyancy-driven effects and turbulence. Optimizing parameters such as j, z, w_l, and Ri can improve electrolyser performance, paving the way for more efficient hydrogen production technologies. These advancements are critical for accelerating the transition to a low-carbon future.