Detailed understanding of bubbles growing on a solid surface is a fundamental requirement in many technological domains, with particular application to water electrolysis in relation to the present-day socio-economic significance of clean energy transition. Evolution of bubbles at the electrode surface greatly determines the overall efficiency and throughput of an electrolysis cell. Bubbles residing on the electrode surface creates resistance to the flow of electric current and reduces the active electro-catalytic area. Therefore, fast removal of the bubbles is desirable for efficient operation. With this motivation, this dissertation aims to build deeper understanding of the bubble dynamics during the pre-detachment and detachment stage. To this end, single hydrogen bubbles grown on microelectrodes are chosen as the object of study.
Thermocapillary and electric forces acting on an electrolytic bubble are introduced and a thorough account of the forces acting on the bubble is taken. A dynamical model of the bubble motion is developed.
By means mathematical and physical modeling of the forces, working mechanism is provided for a novel mode of bubble detachment, namely oscillatory bubble detachment. The model predictions of oscillation parameters are in good correlation with experimental observations. Furthermore, the equation of motion of the bubble is shown to undergo bifurcation thus providing mathematical reasoning behind the existence of different detachment modes. A deeper look is taken specifically at the oscillatory mode. The electrolyte flow velocity is computed and compared with PTV based measurements. Force variation during one oscillation cycle is characterized and correlated with relevant geometric and operational parameters. Based on dynamical conditions of the bubble motion, the surface charge at the bubble interface is quantified. The calculated values match with literature values from bubble electrophoresis experiments.
A detailed look is also taken at the effect of electrode size on the thermocapillary effect. The temperature and flow velocity field in the electrolyte is computed for various electrode size. Additional details regarding the flow structure were found. The location of the interfacial temperature hotspot was quantified. The current density distribution along the electrode surface was found to be strongly non-uniform. The Marangoni and the hydrodynamic force acting on the bubble was quantified at various electrode sizes. Further a model was developed to approximate the thermocapillary effect of a bubble on a large electrode. The location of temperature hotspot was found to be different when compared to bubbles on a microelectrode. This influences the Marangoni flow structure and also the Marangoni force on the bubble.
Overall, this dissertation provides a systematic framework for characterizing forces acting on the bubble and investigating the dynamics of the bubble motion, which adds to our current understanding of bubble evolution and, takes one step towards predictive detachment models.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:87054 |
| Date | 08 September 2023 |
| Creators | Hossain, Syed Sahil |
| Contributors | Eckert, Kerstin, Mutschke, Gerd, Deen, Niels, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 10.1016/j.electacta.2018.11.187, 10.1103/PhysRevLett.123.214503, 10.1016/j.electacta.2020.136461, 10.1039/D1CP00978H, 10.1039/D2CP02092K, 10.1103/PhysRevE.106.035105 |
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