Review—Physicochemical Hydrodynamics of Gas Bubbles in Two Phase Electrochemical Systems

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.

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors

“…60,63 Additionally, liquid convection resulting from other detaching bubbles can promote an earlier detachment than theoretically predicted for stagnant electrolytes. 7,23,62 The following subsections go beyond these spontaneous removal methods and cover engineering strategies for passive bubble removal.…”

Investigating the Integrity of Graphene towards the Electrochemical Oxygen Evolution Reaction

“…As shown above, an important factor to consider in terms of material integrity in the OER in the degradation of the graphene sheet is the physical movement of the generated oxygen bubbles themselves, which are generated at edge plane sites/defects. Electrochemical systems have been reported to suffer poor management of evolving gas bubbles . Gas formation can be divided in four stages that occur simultaneously on the surface of the electrode: nucleation, growth, detachment and rise .…”

“…Electrochemical systems have been reported to suffer poor management of evolving gas bubbles. [23] Gas formation can be divided in four stages that occur simultaneously on the surface of the electrode: nucleation, growth, detachment and rise. [24] In order to capture the graphene damage due to O 2 evolution, as a result of the OER occurring at the various graphene electrodes/surfaces, as it takes place, in situ images were captured, showing a mono-layer graphene electrode while CA was applied (at + 1.61 V (vs. RHE)).…”

Translating batch electrochemistry to single-pass continuous flow conditions: an organic chemist’s guide

“…While in batch the gas simply moves to the headspace, in continuous flow reactors, with no head space available, the generated H 2 affects the cell performance. The behavior of the gas phase and its effect on the flow electrolysis has been studied in detail [37][38][39]. Gas generation typically results in gas/liquid segments in a flow reactor.…”

“…Depending on the flow regime, this might have a positive effect by promoting turbulence. Increasing the operating pressure of the flow cell has been suggested as a possible solution to minimize the issues associated with the generation of gas by reducing the size of the segments [37][38][39]. High pressure could also have a negative effect on the current efficiency by incrementing the amount of H 2 dissolved in the liquid phase, aiding its oxidation on the anode [40].…”