UC Irvine

As green hydrogen becomes increasingly important for advancing carbon neutrality today, the need for improving the efficiency of water electrolysis is emphasized. Water electrolysis technologies include anion exchange membrane, proton exchange membrane, solid oxide, and alkaline electrolyzers. This research focuses on alkaline electrolyzers. Alkaline water electrolysis is the most established technology but still has rooms for improvement. A major bottleneck in alkaline water electrolysis is the formation of gaseous products during the oxygen evolution reaction. The presence of bubbles on electrodes reduces number of active sites, requiring higher overpotential. It has been known that proper management of bubble dynamics plays a crucial role in enhancing electrolysis performance. Therefore, understanding the dynamics of gas generation from electrochemical processes is vital. However, there is still a lack of knowledge regarding bubble dynamics that hampers electrochemical reactions at high current densities. The knowledge gap derives from the complexity of mass transfer phenomena at high current densities and the challenges of examining intense bubble activity at the electrolyte-electrode interface. Investigating bubble evolution within porous media has been particularly challenging due to the limitations of conventional cameras. However, advancements in image sensor technology open up new possibilities for unveiling the physics behind these limitations. As one example, event-based cameras utilize an advanced imaging technique that mimics the way biological eyes process visual information. Leveraging the capabilities of event-based cameras, this study provides an in-depth analysis of gas bubble generation during electrochemical processes and its impact on performance during alkaline water electrolysis. For this, we have explored two types of electrodes in this study: flat coppers and porous nickel foams. The findings suggest that poor mass transport in porous media may lead to an increase in local current density at electrolyte-electrode interfaces, which can interactively have a great influence on bubble dynamics and transport. Furthermore, distinct aspects of bubble behaviors at different overpotential regions are characterized using quantitative analysis. The observation indicates that a decrease in bubble release rate is closely related to the transition to a mass transport-dominated regime, possibly caused by intense coalescence at high current densities. Overall, the study has great significance that controlling bubble dynamics during the electrolysis process is essential for improving performance by overcoming mass transport limitations.