Detachment characteristics of electrolytic bubbles

Çayan Demirkır

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

Water electrolysis is a techniqueby which hydrogen gas (H2) can be obtained by splitting the H2Omolecules. This method is especially attractive due to its compatibility withrenewable power sources, offering a sustainable pathway for hydrogenproduction. However, the efficiency of water electrolysis is significantlyaffected by the formation of gas bubbles during the electrochemical watersplitting. Understanding and optimizing bubble dynamics in water electrolysis are therefore crucial for advancing this technology and supporting the broadertransition to sustainable energy systems.

This thesis investigates various aspects of bubble dynamics during waterelectrolysis, with a focus on bubble detachment characteristics under differentconditions. The research is divided into four main chapters, each addressingspecific aspects of bubble behavior.

Chapter 1 examines the detachmentof isolated hydrogen bubbles due to buoyancy during electrolysis. The studyrevealed that electrolyte concentration influences the contact line formationof the bubbles. Experimental evidences demonstrated that the well-known Fritzexpression is not applicable for predicting bubble detachment on real(non-ideal) surfaces, and the detachment radius of isolated bubbles can bepredicted by the dynamic contact angles.  Chapter 2 focuses on bubble dynamics duringthe hydrogen evolution reaction on a platinum microelectrode, investigating theinfluence of electrolyte composition. The study found that microbubblecoalescence efficiency follows the Hofmeister series of anions across differentelectrolytes. Solutal Marangoni convection, driven by ion concentrationgradients, was identified as a significant factor affecting bubble detachment. InChapter 3, the detachment conditions of wall-attached bubbles throughcoalescence-induced detachment are investigated. Combining experimentalobservations and numerical simulations, the study revealed new insights intothe contact line motion of coalescing spreading bubbles. Adhesion energy andviscous dissipation were found to be important parameters in determining coalescenceresults for bubbles of comparable sizes. Finally, the dynamics of hydrogenbubble pairs produced during water electrolysis using a dual platinummicroelectrode setup are studied in Chapter 4. It is demonstrated thatbubble coalescence leads to earlier departure and higher reaction ratescompared to buoyancy-driven detachment alone. The electrode spacingoptimization was found to significantly enhance mean current in electrolysissystems, resulting in performance improvements of up to 2.4 times compared tousing a single electrode under the same conditions.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Twente
Supervisors/Advisors
  • Lohse, Detlef, Supervisor
  • Krug, Dominik Johannes, Supervisor
Award date5 Nov 2024
Place of PublicationEnschede
Publisher
Print ISBNs978-90-365-6268-3
Electronic ISBNs978-90-365-6269-0
DOIs
Publication statusPublished - 5 Nov 2024

Keywords

  • Water electrolysis
  • Bubble dynamics
  • Detachment
  • Solutal Marangoni effect
  • Coalescence

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