Direct Measurements of Electroviscous Phenomena in Nafion Membranes.

Investigation of electroviscous effects is of interest to technologies that exploit transport of ions through ion exchange membranes, charged capillaries, and porous media. When ions move through such media due to a hydrostatic pressure difference, they interact with the fixed charges, leading to an increased hydraulic resistance. Experimentally this is observed as an apparent increase in the viscosity of the solution. Electroviscous effects are present in all electrochemical membrane-based processes ranging from nanofiltration to fuel-cells and redox flow batteries. Direct measurements of electroviscous effects varying the applied ionic current through Nafion membranes have, to the best of the authors' knowledge, not yet been reported in literature. In the current study, electroviscous phenomena in different Nafion ion exchange membranes are measured directly with a method where the volume permeation is measured under constant trans-membrane pressure difference while varying the ion current density in the membrane. The direct measurement of the electroviscous effect is compared to the one calculated from the phenomenological transport equations and measured transport coefficients. Within the experimental uncertainty, there is a good agreement between the two values for all membranes tested. We report here an electroviscous effect for all Nafion membranes tested to be κH?κH-1=1.15-0.052+0.035.

Data on flow cell optimization for membrane-based electrokinetic energy conversion.

This article elaborates on the design and optimization of a specialized flow cell for the measurement of direct conversion of pressure into electrical energy (Electrokinetic Energy Conversion, EKEC) which has been presented in Østedgaard-Munck et al. (2017) [1]. Two main flow cell parameters have been monitored and optimized: A) the hydraulic pressure profile on each side of the membrane introduced by pumps recirculating the electrolyte solution through the flow fields and B) the electrical resistance between the current collectors across the combined flow cell. The latter parameter has been measured using four-point Electrochemical Impedance spectroscopy (EIS) for different flow rates and concentrations. The total cell resistance consists of contributions from different components: the membrane [Formula: see text], anode charge transfer [Formula: see text], cathode charge transfer [Formula: see text], and ion diffusion in the porous electrodes [Formula: see text]. The intrinsic membrane properties of Nafion 117 has been investigated experimentally in LiI/I2 solutions with concentrations ranging between 0.06 and 0.96 M and used to identify the preferred LiI/I2 solution concentration. This was achieved by measuring the solution uptake, internal solution concentration and ion exchange capacity. The membrane properties were further used to calculate the transport coefficients and electrokinetic Figure of merit in terms of the Uniform potential and Space charge models. Special attention has been put on the streaming potential coefficient which is an intrinsic property.