scholarly journals Ion mobility and partition determine the counter-ion selectivity of ion exchange membranes

2020 ◽  
Author(s):  
Matthias Wessling
Keyword(s):  
Ion Exchange ◽  
Ion Mobility ◽  
Ion Selectivity ◽  
Quantitative Relation ◽  
Ion Exchange Membranes ◽  
Membrane Conductivity ◽  
Counter Ion ◽  
Counter Ions ◽  
New Perspective ◽  
Two Parameters

Ion (perm)selectivity and conductivity are the two most essential properties of an ion exchange membrane, yet no quantitative relation between them has been suggested. In this work, the selectivity between two different counter-ions is correlated to the membrane conductivity. We show that the counter-ion selectivity measured by conventional electrodialysis (ED) can be expressed by the product of two parameters: (a) the mobility ratio between these two different counter-ions in the membrane and (b) their partition coefficient between the solution and the membrane. This is reminiscent of the classical solution-diffusion model. Via the counter-ion mobility in the membrane, the selectivity could be simply expressed with the membrane conductivity and dimensional swelling degree at pure counter-ion forms and at mixed counter-ion form when the membrane has been equilibrated with 1:1 equivalence ratio of the two counter-ions in the solution. This correlation is validated experimentally for the ion selectivity of K+/Na+ in two commercial hydrocarbon-based cation exchange membranes (CEMs). For K+/Na+ in a commercial perfluorosulfonic CEM, and for Mg2+/Na+ in all the three types of CEMs, the correlation could predict the counter-ion partition very well; but there is an underestimation of the K+/Na+ and Mg2+/Na+ mobility ratios afforded by this correlation, which might be due to simplification of the cation activity coefficients in CEMs. This work offers a convenient method to decouple experimentally the effect of partition and mobility in controlling the membrane selectivity, and also proposes a new perspective to study the selectivity as well as conductivity of ion exchange membranes.

scholarly journals Application of counter-ion condensation in calculating the ion activity coefficients for interpreting the membrane selectivity

2021 ◽  
Author(s):  
Matthias Wessling
Keyword(s):  
Ionic Conductivity ◽  
Activity Coefficients ◽  
Experimental Approach ◽  
Average Distance ◽  
Ion Selectivity ◽  
Monovalent Cation ◽  
Homogeneous Distribution ◽  
Linear Charge Density ◽  
Membrane Conductivity ◽  
Counter Ion

The transport selectivity of different cations through cation exchange membranes (CEMs) could be estimated with the partition coefficient (K_j^i) and the cation mobility ratio in the membrane ((u_m^i)⁄(u_m^j )), which in turn can be related to corresponding membrane conductivity and dimensional swelling degree data [Journal of Membrane Science, 2020, 597, 117645]. This method has been validated in two hydrocarbon-based CEMs, and the obtained K+/Na+ selectivity equals to the one obtained with conventional electrodialysis (ED) method. However, the K+/Na+ selectivity of perfluorosulfonic acid (PFSA) membranes, and the bi-/monovalent cation (Mg2+/Na+) selectivity of all three types of CEMs estimated with this ionic conductivity experimental approach deviate noticeably from corresponding values obtained with ED. In this work, it is proved that this deviation is mostly due to the simplification of cation activity coefficients in the membrane. Here, the cation activity coefficients in three types of CEMs are calculated according to Manning`s counter-ion condensation model. In this model, the Manning parameter (ξ) characterizing the dimensionless linear charge density is determined by the average distance between two adjacent fixed sulfonate groups (b) and the permittivity of hydrated membranes (ε). In hydrocarbon-based CEMs, the average distance between fixed sulfonate groups can be estimated by assuming homogeneous distribution of the fixed groups, while in PFSA membranes three representative structure models are employed to estimate this average distance. After accounting for the cation activity coefficients in the membrane, the cation transport selectivity obtained with the ionic conductivity experimental approach agrees well with the selectivity obtained with the ED method. This work shows the importance of cation activity coefficients in the membrane phase in interpreting the membrane transport properties, and complements the proposed conductivity approach to characterize the counter-ion selectivity of ion exchange membranes.

SPEEK/PVDF binary membrane as an alternative proton-exchange membrane in vanadium redox flow battery application

2016 ◽  
Vol 29 (2) ◽  
pp. 127-132 ◽  
Author(s):  
Ling Zhao ◽  
Fuzhen Li ◽  
Yanqing Guo ◽  
Yilun Dong ◽  
Jinying Liu ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Polyvinylidene Fluoride ◽  
Ion Selectivity ◽  
Proton Exchange ◽  
Vanadium Redox Flow Battery ◽  
Ion Exchange Membranes ◽  
Redox Flow Battery ◽  
Flow Battery ◽  
Decay Test ◽  
Vanadium Redox

Sulfonated polyether ether ketone (SPEEK)/polyvinylidene fluoride (PVDF) blends are employed to prepare the ion-exchange membranes for vanadium redox flow battery (VRB) application. The addition of the highly crystalline and hydrophobic PVDF effectively confines the swelling behavior of SPEEK. The vanadium ion permeability of SPEEK/PVDF membranes is one order of magnitude lower than that of Nafion117 membrane and SPEEK membrane. In VRB single-cell test, the SPEEK/PVDF binary membranes exhibit higher energy efficiency (EE) than recast SPEEK and Nafion117 at 30 mA cm−2. The blend membrane with 30 wt% of PVDF (S0.7P0.3) shows EE of 83.2% at 30 mA cm−2, which is superior to that of the Nafion117 and recast SPEEK membranes. In the self-discharge test, S0.7P0.3 membrane also possesses twice longer duration in open circuit decay test. These results indicate that the addition of PVDF is a simple and efficient way to improve the ion selectivity of SPEEK. With all the good properties and low cost, the SPEEK/PVDF membranes are expected to have excellent commercial prospects as ion-exchange membranes for VRB system.

Transport reaction through ion-exchange membranes: modelling of ligand transport by a complexing counter-ion and experiments wih ammine and polyborate ions

Desalination ◽  
1988 ◽  
Vol 68 (2-3) ◽  
pp. 131-148 ◽  
Author(s):  
D. Langevin ◽  
M. Métayer ◽  
M. Labbé ◽  
B. Pollet ◽  
M. Hankaoui ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Ion Exchange Membranes ◽  
Transport Reaction ◽  
Counter Ion ◽  
Ligand Transport

scholarly journals Suppressing vanadium crossover using sulfonated aromatic ion exchange membranes for high performance flow batteries

2020 ◽  
Vol 1 (7) ◽  
pp. 2206-2218
Author(s):  
Tongshuai Wang ◽  
Junyoung Han ◽  
Kihyun Kim ◽  
Andreas Münchinger ◽  
Yuechen Gao ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Ion Transport ◽  
Transport Properties ◽  
High Performance ◽  
Ion Selectivity ◽  
Ion Exchange Membranes ◽  
Flow Battery ◽  
The Right ◽  
Exchange Membrane ◽  
Performance Flow

Novel ion exchange membrane with just the right width of selective aqueous ionic domain (<0.6 nm) and unique functionalities show extraordinary ion selectivity. These unique ion transport properties of our membrane is reflected in a remarkable flow battery performance.

Ion mobility and conductivity of hybrid ion-exchange membranes incorporating inorganic nanoparticles

2011 ◽  
Vol 188 (1) ◽  
pp. 129-131 ◽  
Author(s):  
E. Yu. Safronova ◽  
V.I. Volkov ◽  
A.B. Yaroslavtsev
Keyword(s):  
Ion Exchange ◽  
Ion Mobility ◽  
Inorganic Nanoparticles ◽  
Ion Exchange Membranes
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