Origin of Limiting and Overlimiting Currents in Bipolar Membranes

Area of Science:

• Electrochemistry
• Materials Science
• Environmental Engineering

Background:

• Bipolar membranes (BPMs) facilitate electrochemical water dissociation/recombination, crucial for environmental tech.
• Understanding ion transport in BPMs is vital for optimizing applications like pH control and resource recovery.
• Current knowledge of ion transport dynamics, especially at the BPM junction, remains limited.

Purpose of the Study:

• To theoretically and experimentally investigate ion transport in BPMs under various bias conditions.
• To model the behavior of H+, OH-, and salt ions within BPMs.
• To correlate ion transport phenomena with observed current-voltage characteristics.

Main Methods:

• Utilized the Nernst-Planck theory for modeling ion transport.
• Developed a model requiring only membrane thickness, charge density, and pK of proton adsorption.
• Experimentally validated the model using a commercial BPM and measured current-voltage curves.

Main Results:

• Successfully predicted ion concentration profiles (H+, OH-, Na+, Cl-) within the BPM.
• The model accurately reproduced experimental current-voltage curves, including limiting and overlimiting currents.
• Identified specific concentration profiles responsible for limiting and overlimiting currents.

Conclusions:

• The Nernst-Planck based model provides significant insights into BPM physical phenomena.
• The model's predictive capability aids in understanding and optimizing BPMs for environmental applications.
• This research facilitates the identification of optimal operating conditions for BPMs in resource recovery and carbon capture.