Dynamic equilibrium of electrochemical bubbles growing on micro-electrodes

TL;DR

This paper investigates the conditions under which electrochemical bubbles on micro-electrodes reach a dynamic equilibrium, balancing growth and dissolution, with implications for improving electrolysis efficiency.

Contribution

It extends existing analytical models by incorporating non-uniform gas distribution from simulations, identifying stability regions and conditions for bubble equilibrium.

Findings

Bubbles can reach stable equilibrium states at low oversaturation.

The non-uniform gas distribution significantly influences bubble stability.

Insights suggest ways to enhance electrolysis efficiency.

Abstract

In gas evolving electrolysis, bubbles grow at electrodes due to a diffusive influx from oversaturation generated locally in the electrolyte by the electrode reaction. When considering electrodes of micrometer-size resembling catalytic islands, bubbles are found to approach dynamic equilibrium states at which they neither grow nor shrink. Such equilibrium states are found at low oversaturation for both, pinning and expanding wetting regimes of the bubbles and are based on the balance of local influx near the bubble foot and global outflux. Unlike the stability of pinned nano-bubbles studied earlier, the Laplace pressure plays a minor role only. We extend the analytical solution of Zhang & Lohse (2023) by taking into account the non-uniform distribution of dissolved gas around the bubble obtained from direct numerical simulation. This allows us to identify the parameter regions of bubble growth, dissolution and dynamic equilibrium as well as to analyze the stability of the equilibrium states. Finally, we draw conclusions on how to possibly enhance the efficiency of electrolysis.