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Turkish Journal of Chemistry

Abstract

In processes such as electrodialysis, the applied electrical potential is constrained by concentration polarization at the membrane/solution interface. This polarization, which intensifies at higher current densities, impedes ion transport efficiency and may lead to problems such as salt precipitation, membrane degradation, and increased energy consumption. Therefore, understanding concentration polarization is essential for enhancing membrane performance, improving efficiency, and reducing operational costs. This study investigates the impact of ammonia buffer (NH₄⁺/NH₃) on sulfate ion transport through anion-exchange membranes, with a particular focus on limiting current density and concentration polarization under constant current conditions. Our findings demonstrate that ammonia effectively eliminates concentration polarization and enhances chemical reactions at the membrane interface. Notably, the plateau region in the current-voltage curves (CVCs) was absent, as was the transition time observed in the chronopotentiograms. Furthermore, the Warburg impedance arc in the Nyquist plot of the electrochemical impedance spectra was absent in both limiting and overlimiting current regions and an increasing dominance of the Gerischer arc was registered. At an ammonia concentration of 0.1 M, the influence of concentration polarization on mass transport was effectively mitigated, enabling sulfate counter-ions to pass through the membrane without encountering concentration polarization. The addition of ammonia catalytically accelerated the proton-transfer reactions which accelerates the water dissociation reaction at earlier polarization stages, preventing the formation of diffusion boundary layers and facilitating the transport of sulfate counter-ions through the AMX anion exchange membrane. As a result, the polarization plateau disappeared, and the overlimiting current region shifted closer to the ohmic region, all without affecting the limiting current density (jlim).

Author ORCID Identifier

ABDALLAH TIMMAOUI: 0000-0001-5663-5871

MAHMOUD FERHAT: 0000-0003-2716-8527

NESRİNE FERHAT: 0009-0002-1582-3790

AHMED HAMDI: 0000-0003-3138-4361

DOI

10.55730/1300-0527.3703

Keywords

Ion-exchange membrane, mass transport, concentration polarization, electrodialysis, membrane/solution interface

First Page

843

Last Page

855

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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