Detachment characteristics of electrolytic bubbles

Water electrolysis is a technique by which hydrogen gas (H₂) can be obtained by splitting the H₂O molecules. This method is especially attractive due to its compatibility with renewable power sources, offering a sustainable pathway for hydrogen production. However, the efficiency of water electrolysis is significantly affected by the formation of gas bubbles during the electrochemical water splitting. Understanding and optimizing bubble dynamics in water electrolysis are therefore crucial for advancing this technology and supporting the broader transition to sustainable energy systems.

This thesis investigates various aspects of bubble dynamics during water electrolysis, with a focus on bubble detachment characteristics under different conditions. The research is divided into four main chapters, each addressing specific aspects of bubble behavior. 

Chapter 1 examines the detachment of isolated hydrogen bubbles due to buoyancy during electrolysis. The study revealed that electrolyte concentration influences the contact line formation of the bubbles. Experimental evidences demonstrated that the well-known Fritz expression is not applicable for predicting bubble detachment on real (non-ideal) surfaces, and the detachment radius of isolated bubbles can be predicted by the dynamic contact angles.  Chapter 2 focuses on bubble dynamics during the hydrogen evolution reaction on a platinum microelectrode, investigating the influence of electrolyte composition. The study found that microbubble coalescence efficiency follows the Hofmeister series of anions across different electrolytes. Solutal Marangoni convection, driven by ion concentration gradients, was identified as a significant factor affecting bubble detachment. In Chapter 3, the detachment conditions of wall-attached bubbles through coalescence-induced detachment are investigated. Combining experimental observations and numerical simulations, the study revealed new insights into the contact line motion of coalescing spreading bubbles. Adhesion energy and viscous dissipation were found to be important parameters in determining coalescence results for bubbles of comparable sizes. Finally, the dynamics of hydrogen bubble pairs produced during water electrolysis using a dual platinum microelectrode setup are studied in Chapter 4. It is demonstrated that bubble coalescence leads to earlier departure and higher reaction rates compared to buoyancy-driven detachment alone. The electrode spacing optimization was found to significantly enhance mean current in electrolysis systems, resulting in performance improvements of up to 2.4 times compared to using a single electrode under the same conditions.