Control of hydrogen bubble plume during electrolysis of water

Abstract

Hydrogen bubble plumes are generated from the cathode during electrolysis. The plume formation mechanism contributes to the control of bubble diameters and alignment in solvent. The generation of hydrogen bubbles (HBs) and oxygen bubbles (OBs) from electrodes was observed in tap water and saline using a high-speed microscope. Bubble diameter changes were analysed from the obtained microscopic images, and the growth kinetics of HBs and OBs were compared. The result showed that plume formation was primarily dependent on ion strength of water and not voltage to the electrode. HB diameter change in plume was proportional to the distance from the cathode in tap water. Such correlation between HB diameter and distance from the cathode was not observed in saline. By simultaneous observation of HBs and OBs attached to the electrodes, the increase in HB diameter was faster than that of OB. The kinetic properties in HBs and OBs were proportional to (time)1/2 and (time)1, respectively, suggesting that the diffusion of oversaturated hydrogen gas and pressure difference at OB surfaces were dominant. Based on these results, HB plume formation was determined by the lower gas solubility and mass density of HB than that of OB, as well as controlled by voltage and ionic strength of water.