Insights into hydrogen and vapor bubble dynamics under boiling-promoted conditions in high-rate water electrolysis

High-rate water electrolysis suffers from local thermal accumulation and gas coverage near the electrode surface. In this study, cell-scale electrochemical tests are conducted at varying electrolyte temperatures and pressures to explore electrochemical characteristics under boiling-promoted and boiling-suppressed conditions. The results reveal that additional polarization loss occurs at 373.15 K and 1.0 atm, while pressurization mitigates such loss. A volume of fluid (VOF) model is established to investigate the effects of electrolyte superheat and electrode superheat on hydrogen and vapor mixed bubble evolution. Simulation results show that electrolyte superheat accelerates bubble growth and enlarges bubble contact area. In contrast, electrode superheat promotes earlier bubble detachment with a minor increase in contact radius. Although boiling-related vapor generation enhances local hydrogen transfer by increasing interfacial area, this effect is weakened by enlarged bubble coverage, increased ionic transport resistance, and vapor-dominated bubble growth. Vapor generation tends to exert a negative effect on electrolysis performance, especially under electrolyte superheat conditions.