Insight into Oxygen Transport in Proton Exchange Membrane Water Electrolyzers by In Situ X-Ray Characterization.

Area of Science:

• Electrochemical Engineering
• Materials Science
• Energy Conversion

Background:

• Proton exchange membrane water electrolyzers (PEMWEs) are key for hydrogen production.
• Performance limitations at high current densities stem from insufficient mass transfer insights, particularly oxygen transport.

Purpose of the Study:

• To investigate oxygen transport mechanisms within PEMWEs at high current densities.
• To correlate oxygen transport phenomena with overall electrolytic performance.

Main Methods:

• Utilized in situ X-ray imaging in a novel visual mini-cell to observe bubble dynamics and voltage response.
• Simultaneously characterized bubble nucleation, growth, detachment, and voltage stability.
• Tested porous transport layers (PTLs) under operational conditions up to 9 A cm⁻².

Main Results:

• Identified distinct bubble evolution processes: nucleation, growth, and detachment.
• Revealed critical current densities for both carbon-based and titanium-based PTLs.
• Observed voltage instability and significant oxygen overpotential beyond critical current densities.
• Introduced the interfacial separation zone (ISZ) concept, defining pathways for bubble behavior and exhibiting specific regimes related to current density.

Conclusions:

• Oxygen transport in PEMWEs is governed by bubble dynamics, with critical current densities impacting performance.
• The proposed interfacial separation zone (ISZ) offers a new framework for understanding and potentially mitigating high-current density limitations.
• This research provides a novel approach to enhance PEMWE efficiency through improved mass transfer insights.