The Influence of Current Density on Transport of Vanadium Cations through Membranes with Different Charges

Abstract

Fluxes of the four vanadium cations V2+, V3+, VO2+ and VO2 + through three archetypal membranes were measured as functions of current density. The membranes include a cation-exchange membrane, an anion-exchange membrane, and an initially uncharged membrane. Comprehensive data sets including mass and vanadium sorption, in-plane and through-plane conductivity, diffusive permeability, and transference number were collected to help interpret vanadium fluxes. Conductivity, diffusion coefficient, and transference number appear to be inter-related as predicted by Nernst-Planck theory for the cation-exchange membrane Nafion. The properties do not appear to be as compellingly connected for the anion-exchange membrane FAPQ-330 or polybenzimidazole. The Nernst-Planck formalism, with the Nernst-Einstein approximation, predicts a larger influence of current density on vanadium flux than is observed experimentally for these membranes. Possible explanations for these disparate findings are investigated and discussed.

Transport of Ligand Coordinated Iron and Chromium through Cation-Exchange Membranes

“…Membranes with lower equivalent weights tend to swell more because they need to incorporate more water to dilute the fixed ions and establish equilibrium with the surrounding electrolyte bath. For comparison, Darling et al reported mass sorptions of approximately 0.05 for as received Nafion and 0.25 for fully expanded Nafion immersed in vanadium battery electrolytes, 33 which span the values in Table II. Woo et al gave a water uptake ω = 37% for Aquivion after soaking in de-ionized water at room temperature.…”

“…Darling et al previously reported similarly high sorptions of co-ions: 0.08 moles V 2+ /V 3+ per mole of fixed cations in Fumasep FAPQ, an anion-exchange membrane made by Fumatech, compared to 0.16 moles V 2+ /V 3+ per mole of fixed anions in as received Nafion. 33 Membrane conductivities were calculated from alternating current (AC) impedance measurements on symmetric cells fed from a single electrolyte reservoir. Cells were built with either one or two pieces of membrane and run in K 3/4 Fe(CN) 6 or K 1/2 CrPDTA electrolyte.…”

“…Where ṁ is the mass flow rate in g s −1 calculated from the slopes in Fig. 6, μ = • 1 mPa s is viscosity of water, l is membrane thickness, ρ = − 1 g cm 3 is density of water, A = 14.6 cm 2 is area available for flow, and ΔP = 0.75 MPa is the pressure difference across the 33 The red data points represent Fe(CN) 6 3/4− ions through Aquivion and E-620(K).…”

“…Correlation between diffusion coefficient and hydraulic permeability for different membranes. The blue data points represent vanadyl ions through different membranes in contact with aqueous vanadium sulfate/ sulfuric acid solutions 33. The red data points represent Fe(CN)6 3/4− ions through Aquivion and E-620(K).…”

Size and Charge Effects on Crossover of Flow Battery Reactants Evaluated by Quinone Permeabilities Through Nafion

“…[15][16][17][18] VRFBs were first developed using proton-conducting cation exchange membranes; more recently anion exchange membranes have been shown to suppress the crossover of vanadium cations by charge-based exclusion. 19,20 This strategy of leveraging the charge exclusion effect of membrane ionic moieties remains an opportunity for new redox flow battery chemistries.…”