Abstract
Electrochemical systems suffer from poor management of evolving gas bubbles. Improved understanding of bubbles behavior helps to reduce overpotential, save energy and enhance the mass transfer during chemical reactions. This work investigates and reviews the gas bubbles hydrodynamics, behavior, and management in electrochemical cells. Although the rate of bubble growth over the electrode surface is well understood, there is no reliable prediction of bubbles break-off diameter from the electrode surface because of the complexity of bubbles motion near the electrode surface. Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) are the most common experimental techniques to measure bubble dynamics. Although the PIV is faster than LDA, both techniques are considered expensive and time-consuming. This encourages adapting Computational Fluid Dynamics (CFD) methods as an alternative to study bubbles behavior. However, further development of CFD methods is required to include coalescence and break-up of bubbles for better understanding and accuracy. The disadvantages of CFD methods can be overcome by using hybrid methods. The behavior of bubbles in electrochemical systems is still a complex challenging topic which requires a better understanding of the gas bubbles hydrodynamics and their interactions with the electrode surface and bulk liquid, as well as between the bubbles itself.
Highlights
Electrochemical processes occur at the nano, micro- and macro- scales in numerous applications such as fuel cells, batteries, hydrogen production, mineral extraction, water treatment, electrotherapy, sensors and many others
What is the applicable range of supergravity fields on electrochemical systems to reduce the overpotential? Do the ultrasonic fields always have positive interaction on bubbles detachment? What are the best methods to simulate twophase electrochemical systems? What is the effect of changing bulk flow velocity on the bubble flow regime? Most importantly, the behavior of bubbles in electrochemical systems is still a complex challenging topic which requires a better understanding of the gas bubbles hydrodynamics and their interactions with the electrode surface and bulk liquid, as well as between the bubbles itself
Bubble generation in electrochemical cells plays a significant role in the mass transfer and cell efficiency
Summary
Electrochemical processes occur at the nano-, micro- and macro- scales in numerous applications such as fuel cells, batteries, hydrogen production, mineral extraction, water treatment, electrotherapy, sensors and many others. In addition to this effect on mass transfer, the adhering layer acts as an electrical shield that reduces the conductivity and increases the ohm resistance on the electrode surface.[7] The characteristics of this layer depend on the interfaces between threephases; solid, gas and liquid, which are respectively electrode, bubble, and bulk solution These interfaces are strongly related to the electrode geometry, cavities, wettability, bubble composition, bulk solution chemistry, flow velocity and reaction components (e.g. current density).[8, 9] On the other hand, the detachment and release of bubbles from the electrode surface induces a wake or micro-convection which enhances the mass transfer at the detachment location. The paper covers a review of experimental techniques that are used in the measurement of gas bubbles hydrodynamics
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