Overlimiting Ion Transport and Reaction Limitations in Charged Porous Media
Abstract
Electrochemical reaction rates are controlled by both interfacial charge-transfer kinetics and reactive-ion transport. In charged porous media, fixed charges enrich reactive counterions near pore walls, enabling transport beyond the classical diffusion limit via surface conduction (SC). Under overlimiting conditions, classical Butler-Volmer kinetics predict indefinitely increasing current with overpotential, contrasting with microscopic electron-transfer theories, which impose a finite reaction-limited current. Here, we couple the one-dimensional leaky membrane model to coupled ion-electron transfer (CIET) kinetics to examine the interplay between transport and reaction limitations. The limiting behavior is governed by the scaled surface charge (ρ̃s) and a Damköhler number (Da) comparing reaction-limited and diffusion-limited currents. We derive analytical limiting-current expressions for neutral, positive, and negatively charged porous media, mapping underlimiting-to-overlimiting transitions in the (Da,ρ̃s) plane. By preventing reactive-ion depletion, SC restores polarization-curve sensitivity to charge-transfer kinetics that would otherwise be obscured by diffusion limitation. Fitting to published Cu electrodeposition data in charged AAO membranes yields Da≈24. CIET parameters fitted to AAO(−) also describe AAO(+) and predict a finite AAO(−) reaction limit beyond the applied voltage range. These results provide a framework for distinguishing transport-limited and reaction-limited responses in electrochemical systems and establish charged porous media as platforms to reveal electrochemical reaction-kinetic descriptors.
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BibTeX
@misc{yennemadi2026overlimiting,
title = {{Overlimiting Ion Transport and Reaction Limitations in Charged Porous Media}},
author = {Arjun V. Yennemadi and Junghyun Yoon and Martin Z. Bazant},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.03146},
eprint = {2609.03146},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.03146},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Overlimiting Ion Transport and Reaction Limitations in Charged Porous Media
AU - Arjun V. Yennemadi
AU - Junghyun Yoon
AU - Martin Z. Bazant
PY - 2026
DA - 2026/09/02
PB - arXiv
DO - 10.48550/arxiv.2609.03146
UR - https://arxiv.org/abs/2609.03146
AB - Electrochemical reaction rates are controlled by both interfacial charge-transfer kinetics and reactive-ion transport. In charged porous media, fixed charges enrich reactive counterions near pore walls, enabling transport beyond the classical diffusion limit via surface conduction (SC). Under overlimiting conditions, classical Butler-Volmer kinetics predict indefinitely increasing current with overpotential, contrasting with microscopic electron-transfer theories, which impose a finite reaction-limited current. Here, we couple the one-dimensional leaky membrane model to coupled ion-electron transfer (CIET) kinetics to examine the interplay between transport and reaction limitations. The limiting behavior is governed by the scaled surface charge (ρ̃_s) and a Damköhler number (Da) comparing reaction-limited and diffusion-limited currents. We derive analytical limiting-current expressions for neutral, positive, and negatively charged porous media, mapping underlimiting-to-overlimiting transitions in the (Da,ρ̃_s) plane. By preventing reactive-ion depletion, SC restores polarization-curve sensitivity to charge-transfer kinetics that would otherwise be obscured by diffusion limitation. Fitting to published Cu electrodeposition data in charged AAO membranes yields Da≈24. CIET parameters fitted to AAO(−) also describe AAO(+) and predict a finite AAO(−) reaction limit beyond the applied voltage range. These results provide a framework for distinguishing transport-limited and reaction-limited responses in electrochemical systems and establish charged porous media as platforms to reveal electrochemical reaction-kinetic descriptors.
ER -