Intrabubble coupled evolution of microdroplets and nanobubbles in oxygen evolution reaction

Area of Science:

• Electrochemistry
• Materials Science
• Surface Science

Background:

• Adherent gas bubbles in oxygen evolution reactions (OER) typically impede ion/mass transport and block active sites.
• The role of bubbles in ionomer-based electrodes is often oversimplified, overlooking complex interfacial phenomena.

Purpose of the Study:

• To investigate the intrabubble dynamics on ionomer-coated electrodes during OER.
• To understand how ionomer properties influence bubble behavior and electrode performance.
• To identify strategies for mitigating bubble-induced activity loss.

Main Methods:

• Development of a transparent on-chip electrolyzer for integrated in-situ characterization.
• Utilized optical microscopy, spectroscopic analysis, and atomic force microscopy.
• Analyzed bubble growth, three-phase contact line behavior, and ionomer phase separation.

Main Results:

• Observed characteristic pinning-depinning behavior of the three-phase contact line during bubble growth.
• Discovered the evolution of free water from the ionomer into microdroplets under growing bubbles.
• Identified nucleation of nanobubbles within these microdroplets, a novel intrabubble process enabled by ionomer phase separation.
• Demonstrated preserved electrochemical activity on ionomer-coated electrodes despite bubble coverage, unlike ionomer-free counterparts.

Conclusions:

• Ionomer-based electrodes exhibit complex intrabubble dynamics, including microdroplet and nanobubble formation, which are crucial for maintaining activity.
• Tailoring ionomer phase separation can intensify these processes, leading to improved performance at high current densities.
• This work provides a new perspective on bubble management in OER and opens avenues for mitigating activity loss.