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

Abstract

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 (Rmem), anode charge transfer (RnormalA), cathode charge transfer (RnormalC), and ion diffusion in the porous electrodes (RnormalD).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.

Steady State and Dynamic Response of Voltage-Operated Membrane Gates

“…The LiI/I 2 solutions were prepared using Lithium Iodide, LiI (Sigma-Aldrich: Lithium Iodide Hydrate, 223816, St. Louis, MO, USA), in Milli-Q Water and were saturated with Iodine, I 2 (Sigma-Aldrich: Iodine, 229695). Nafion 212 (Nafion Store: N212, ion exchange capacity 0.95 to 1.01 meq g−1 and thickness of 50 μm in dry conditions) was pre-treated as described earlier [36]. First it was boiled in 3 wt% H 2 O 2 for 1 h, washed in boiling in milli-Q water for 10 min, boiled in 0.05 M sulfuric acid for 30 min, and finally rinsed several times in boiling water.…”

“…The remaining parameters used are: κH=1×10−17 m2 Pa−1 s−1, A=2.5×10−3 m2, Δx=1×10−4 m, and Δp=105 Pa. The values of the parameters have been chosen to be representative of the properties of Nafion 212 membranes [33,36] and of the experimental conditions described in the present work. From the analysis of Equation (3) it is clear that, besides the membrane geometry and trans-membrane pressure difference, the electrical power depends only on the hydraulic permeability and the efficiency of the process which is conveniently expressed by β.…”

Direct Measurements of Electroviscous Phenomena in Nafion Membranes

“…. A similar flow cell has been previously described in more detail in Reference [13]. Figure 1b illustrates the experimental setup.…”

“…Figure 1a illustrates the EKEC concept, where a cation exchange membrane (CEM) has aqueous LiI/I 2 electrolyte solutions of equal concentration on both sides. A pressure gradient (∆p = p high − p low ) drives Li + ions and H 2 O molecules through the membrane while most I 3 are being rejected due to the membrane permselectivity [13]. In order to maintain charge neutrality, the cation transport is balanced by the electrode reaction: 2 I 3 -− − − − 3 I 2 + 2 e -, thus generating an electrical current (I) passing through an external electrical load (represented as a light bulb in Figure 1a).…”

Electro-Osmotic Behavior of Polymeric Cation-Exchange Membranes in Ethanol-Water Solutions

“…The coupling between solvent and charge flows, reflected by the Onsager reciprocity principle, also points to the use of electrokinetic effects for energy conversion. Electrokinetic effects in membrane systems can be utilized for conversion between mechanical and electrical energies [ 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. These systems could also be used as electric generators or electrokinetic pumps [ 11 , 12 , 13 ], and the efficiency of the process strongly depends on the membranes’ properties.…”