Effect of Protolysis Reactions on the Shape of Chronopotentiograms of a Homogeneous Anion-Exchange Membrane in NaH2PO4 Solution
- Authors: Belashova E.D.1, Kharchenko O.A.1, Sarapulova V.V.1, Nikonenko V.V.1, Pismenskaya N.D.1
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Affiliations:
- Kuban State University
- Issue: Vol 57, No 13 (2017)
- Pages: 1207-1218
- Section: Article
- URL: https://journal-vniispk.ru/0965-5441/article/view/179672
- DOI: https://doi.org/10.1134/S0965544117130035
- ID: 179672
Cite item
Abstract
Single-pulse and double-pulse chronopotentiograms of a homogeneous anion-exchange membrane AX in 0.02 M solutions of NaCl (system 1) or NaH2PO4 (system 2) have been recorded in underlimiting and overlimiting current modes. It has been found that in the case of exceeding the limiting current (i > ilimLev) calculated using the convection–diffusion model, the time required to establish a steady state in system 2 increases by more than an order of magnitude compared to system 1. The slow growth of the potential drop is due to a gradual transition of the membrane from the form in which the main counterion is H2PO4– to the HPO42– form. This transition is due to the deprotonation of a part of H2PO4– ions forming HPO42– and protons as they enter the membrane. The participation of H+ in charge transfer in the depleted diffusion layer at a given current density causes a lower value of the potential drop than in system 1 for the same i/ilimLev ratio. In intense current regimes, chronopotentiograms of system 2 exhibit two inflection points. The first point corresponds to the classical Sand transition time and is due to reaching the limiting current of H2PO4– ions (the main charge carrier for i < ilimLev) in the depleted diffusion layer. The second point is associated with a critical current that can be called the second limiting current in the system with NaH2PO4 and has no analogue in the system with NaCl. This current, which is approximately 2ilimLev, corresponds to the state when the membrane is completely transformed into the HPO42– form. Meanwhile, the source of protons due to the transformation of H2PO4– into HPO42– ions as they enter the membrane is exhausted. After reaching this critical value of the potential drop, either the HPO42– deprotonation reaction to give triply charged PO43– ions in the membrane or the water splitting on fixed groups located at the membrane/solution interface may occur.
About the authors
E. D. Belashova
Kuban State University
Author for correspondence.
Email: ekaterinabelashova23@gmail.com
Russian Federation, Krasnodar, 350040
O. A. Kharchenko
Kuban State University
Email: ekaterinabelashova23@gmail.com
Russian Federation, Krasnodar, 350040
V. V. Sarapulova
Kuban State University
Email: ekaterinabelashova23@gmail.com
Russian Federation, Krasnodar, 350040
V. V. Nikonenko
Kuban State University
Email: ekaterinabelashova23@gmail.com
Russian Federation, Krasnodar, 350040
N. D. Pismenskaya
Kuban State University
Email: ekaterinabelashova23@gmail.com
Russian Federation, Krasnodar, 350040
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