Advances in bubble dynamics during (photo)electrochemical water splitting for hydrogen production

Water splitting has emerged as one of the most promising strategies for sustainable hydrogen production, which is widely recognized as a cornerstone for future carbon-neutral energy systems. Despite decades of research on catalysts, electrodes, and reactor designs, comparatively little attention has historically been paid to the role of gas bubbles generated during electrochemical (EC) and photoelectrochemical (PEC) water splitting. Bubble dynamics, however, play a decisive role in determining the overall energy efficiency and operational stability of these systems. The accumulation of bubbles at electrode surfaces reduces the effective electrochemically active area, increases ohmic resistance and activation overpotentials, and in the case of PEC systems, additionally causes light scattering and optical energy loss. These combined effects can significantly diminish reaction kinetics and device durability. With the advancement of in situ/operando characterization techniques and multiscale modeling, the fundamental and practical importance of bubble dynamics in hydrogen evolution has become increasingly evident in recent years. This review provides a comprehensive survey of bubble behaviors in both EC and PEC water splitting systems. We begin by outlining the fundamental processes of bubble nucleation, growth, coalescence, and detachment, with emphasis on the dynamic features of single bubbles and their interactions with the electrode-electrolyte interface. A comparative analysis is presented to highlight the similarities and distinct challenges of bubble effects in purely EC versus PEC water splitting systems. We further discuss how localized concentration gradients, interfacial wettability, and external field effects jointly shape bubble evolution and mass transport. Beyond mechanistic understanding, considerable progress has been made in bubble management strategies, which can be broadly divided into passive and active approaches. Passive methods focus on tailoring electrode morphology, surface chemistry, and wettability to promote rapid bubble release and minimize electrode blockage. Active control strategies, by contrast, utilize external fields (e.g., electric, magnetic, acoustic, or hydrodynamic) or system-level engineering measures such as high-pressure operation to achieve precise control over bubble detachment and transport. We summarize representative advances in both categories, evaluate their effectiveness in enhancing hydrogen production rates and device stability, and discuss their applicability to different EC and PEC configurations. Special attention is given to the trade-offs inherent in each strategy, including complexity of implementation, scalability, and energy cost.Finally, the review highlights key challenges and outlines future directions for research. These include the need for a quantitative understanding of the coupling between current density and bubble properties (e.g., size distribution, surface coverage, growth dynamics, and mass-transfer efficiency), particularly under industrially relevant high-current-density conditions. In summary, bubble management is now recognized as a crucial factor in achieving efficient and durable water splitting. Establishing a mechanistic foundation for bubble dynamics across length and time scales, combined with rational design of control strategies, will pave the way toward next-generation EC and PEC devices for sustainable hydrogen production.