The effect of buoyancy driven convection on the growth and dissolution of bubbles on electrodes

TL;DR

This study combines experiments and simulations to show that buoyancy-driven natural convection significantly influences bubble growth and dissolution on electrodes, impacting water electrolysis efficiency.

Contribution

It demonstrates the importance of including solutal-driven natural convection in models, revealing how bubble spacing and current density affect bubble dynamics.

Findings

Convection patterns depend on bubble spacing and current density.

Large bubble spacing promotes convective instability.

Including natural convection improves modeling accuracy.

Abstract

Enhancing the efficiency of water electrolysis, which can be severely impacted by the nucleation and growth of bubbles, is key in the energy transition. In this combined experimental and numerical study, in-situ bubble evolution and dissolution processes are imaged and compared to numerical simulations employing the immersed boundary method. We find that it is crucial to include solutal driven natural convection in order to represent the experimentally observed bubble behaviour even though such effects have commonly been neglected in modelling efforts so far. We reveal how the convective patterns depend on current densities and bubble spacings, leading to distinctively different bubble growth and shrinkage dynamics. Bubbles are seen to promote the convective instability if their spacing is large ($\geq4$mm for the present conditions), whereas the onset of convection is delayed if the inter-bubble distance is smaller. Our approach and our results can help devise efficient mass transfer solutions for gas evolving electrodes.