Measurement of ion transport properties in ion exchange membranes for photoelectrochemical water splitting

Abstract

Photoelectrochemical (PEC) water-splitting systems have the unique ability to produce renewable hydrogen directly from sunlight, independent of the electrical grid. These systems are therefore appealing technological options for resilient long-term energy storage. Ion selective membranes, such as monopolar and bipolar membranes, are a vital component of PEC water-splitting systems. These membranes allow for ionic conduction between the cathode and anode chambers, separation of products, and improved catalyst environments for reactions. In order to measure key properties and to study the performance of these ion exchange membranes, it is imperative to develop a robust testing protocol that can be used across the field. This paper introduces two standard electrochemical cells designed to directly measure ion transport properties in monopolar and bipolar membranes. The first electrochemical cell uses commercially available Pt disk electrodes to preform electrochemical impedance spectroscopy (EIS) and reliably measure through-plane conductivity of monopolar membranes. The second electrochemical cell uses four-point measurements with Luggin capillaries and a series of membrane configurations to perform current density-voltage and Faradaic efficiency (FE) measurements for water dissociation (WD) reactions on bipolar membranes. The cell designs and techniques laid out below allow for accurate measurement of ion transport parameters in ion exchange membranes, direct comparison of membranes being developed across the field, and in turn, greater advancements in ion exchange membranes and PEC water-splitting systems.

Analysis of bipolar membranes for electrochemical CO2capture from air and oceanwater

“…The choice of a 4-probe measurement (and simulation) is critical because it enables the decoupling of the potential losses that occur at the anode and cathode from those that result from and drive transport and kinetics in the BPM. 43 For the purposes of the simulations and energy intensity calculations, we defined the energy intensity of the BPM-ED processes as the membrane potential in the 4-probe experimental cell since the energetics of the terminal electrodes are not directly correlated with the rate of CO 2 efflux or sorbent regeneration in the BPM. Moreover, the terminal electrodes are often used to perform reactions that produce value-added streams in EMCC processes.…”

Exploring Bipolar Membranes for Electrochemical Carbon Capture

“…The choice of a 4-probe measurement (and simulation) is critical because it enables the decoupling of the potential losses that occur at the anode and cathode from those that result from and drive transport and kinetics in the BPM. 43 For the purposes of the simulations and energy intensity calculations, we defined the energy intensity of the BPM-ED processes as the membrane potential in the 4-probe experimental cell since the energetics of the terminal electrodes are not directly correlated with the rate of CO2 efflux or sorbent regeneration in the BPM. Moreover, the terminal electrodes are often used to perform reactions that produce value-added streams in EMCC processes.…”

Asymmetric Bipolar Membrane for High Current Density Electrodialysis Operation with Exceptional Stability

“…Luggin capillaries holding Ag/AgCl reference electrodes (CHI111, CH Instruments) were placed in the acid and base chambers to allow for the most direct measurement of the voltage across the BPM. 18 Chronopotentiometry: After the electrodialysis cell described above was assembled, potentiostat (Biologic SP 300, Biologic SP 200, Kiethley 2400) leads were attached in a four-point measurement configuration so that a current could be applied across the full cell and the resulting voltage could be measured directly across the BPM.…”

“…Titration was used for more pH values > 12 and < 2. All pH titration measurements and the subsequent calculation of theoretical H + /OHconcentration and Faradaic efficiency were performed as reported in É Lucas et al 18 Low vacuum SEM: All SEM images were obtained using the low vacuum mode on an FEI Nova NanoSEM 450. A spot size of 5.0 and a voltage of 10.00 kV was used for most images.…”

“…The ability to sustain large differences in pH allows for cathode and anode local reaction environments that are ideal for attaining high activity, selectivity, and stability of electrocatalysts based on earth-abundant elements. [13][14][15][16][17][18][19] BPMs have also shown promise when integrated into salt-water fed electrodialysis cells used for pH swingbased direct air capture (DAC) [20][21][22] or extraction of dissolved inorganic carbon from ocean water for direct ocean capture (DOC) and ocean deacidification. 6,9,23 Stable BPM operation at high current densities (~ 1 A cm -2 ) and low voltages (< 1.5 V) is critical to achieve low capital and operating costs in various electrochemical devices.…”