Determination of Ionic Diffusion Coefficients in Ion‐Exchange Membranes: Strong Electrolytes and Sulfates with Dissociation Equilibria

Abstract

Ionic diffusion coefficients in the membrane are needed for the modelling of ion transport in ion‐exchange membranes (IEMs) with the Nernst‐Planck equation. We have determined the ionic diffusion coefficients of Na+, OH−, H+, Cl−, SO42−, NaSO4−, and HSO4− from the diffusion experiments of dilute NaCl, NaOH, HCl, Na2SO4, and H2SO4 solutions through IEMs and the membrane conductivity measured in these solutions, using electrochemical impedance spectroscopy. The order of diffusion fluxes across the anion‐exchange membrane is found to be as H2SO4>HCl>NaCl>Na2SO4>NaOH, whereas for the cation‐exchange membrane it was NaOH>NaCl>Na2SO4≥H2SO4. Special attention is given to sulfates because of the partial dissociation of bisulfate and NaSO4−, which makes the use of the Nernst‐Hartley equation, that is, splitting the electrolyte diffusion coefficient into its ionic contributions, impossible. The expression of the diffusion coefficient of sulfates taking into account the dissociation equilibrium has been derived and the corresponding Fick equation has been integrated. In addition, for sulfates, finite element simulations with COMSOL Multiphysics, applying a homogeneous membrane model, were done to give estimates of their ionic diffusion coefficients. This work offers a convenient approach to finding diffusion coefficients of various ions inside IEMs.

Controllable Carbon Felt Etching by Binary Nickel Bismuth Cluster for Vanadium–Manganese Redox Flow Batteries

“…Accordingly, we coated the Ni precursor first on the surface of CF by ultrasonication (Figure S6). NiO was formed on the carbon felt through the thermal decomposition reaction of nickel nitrate at 300 °C . At 500 °C, Bi 2 O 3 had formed via the thermal decomposition of bismuth nitrate, and then Bi 2 O 3 chemically reacted with NiO to form Bi–Ni oxide on the carbon felt surface .…”

“…At 500 °C, Bi 2 O 3 had formed via the thermal decomposition of bismuth nitrate, and then Bi 2 O 3 chemically reacted with NiO to form Bi–Ni oxide on the carbon felt surface . Finally, the NB-ECF was prepared by carbothermic reduction of NiO, Bi 2 O 3 , and Bi–Ni oxides at 700 °C for 3 h. ,, For comparison, we prepared more Ni x Bi 100– x -CF ( x = 0, 25, 75, and 100) samples according to the weight ratio of the Ni and Bi precursors.…”

Bipolar membrane electrodialysis of Na2CO3 and industrial green liquor for producing NaOH: A sustainable solution for pulp and paper industries

“…Commercially available membranes (CR61P, AR103P, composed of inert reinforcing fibers and ion-exchange resins) from Suez Water Technologies and Solutions are used in this study; their properties are described in our previous articles [13][14]. The BPM is a sandwich of CR61P and AR103A, treated with Fe(III); it was used as received.…”