Free-Energy Analysis of Bubble Nucleation on Electrocatalytic Surfaces

TL;DR

This paper develops a free-energy model to predict bubble nucleation behavior on electrocatalytic surfaces, providing insights into activation energy, critical nucleus size, and supersaturation effects to enhance electrolyzer performance.

Contribution

It introduces a quantitative free-energy framework for bubble nucleation, linking supersaturation, temperature, pressure, and wettability, with validation against experimental data.

Findings

Activation energy decreases as supersaturation increases, following a power-law of $ ilde{ ext{zeta}}^{-2}$.

Critical nucleus radius scales inversely with supersaturation, as $ ilde{ ext{zeta}}^{-1}$.

Model predictions for hydrogen, oxygen, and nitrogen bubbles match experimental measurements.

Abstract

Bubble nucleation at catalyst surfaces plays a critical role in the operation of electrolyzers. However, achieving controlled bubble nucleation remains challenging due to limited understanding of the underlying mechanisms. Here, we present a free-energy model that quantitatively predicts both the activation energy and critical nucleus size of bubbles at given supersaturation, temperature, pressure, and surface wettability. We find that the activation energy $\Delta G_{max}$ decreases with increasing supersaturation $\zeta$, following a power-law scaling of $\Delta G_{max} \sim \zeta^{-2}$, while the critical nucleus radius $R_c$ scales as $R_c\sim \zeta^{-1}$. Our theoretical predictions for the critical nucleus radius of hydrogen, oxygen and nitrogen bubbles are in quantitative agreement with experimental measurements. Finally, we present a simple model that couples gas diffusion and electrochemical reaction kinetics to determine the maximum gas supersaturation at a given current density. Our results advance the fundamental understanding of bubble nucleation at catalyst surfaces and provide practical guidelines for catalyst layer design to improve the performance of electrolyzers.