Reducing Ohmic Resistances in Membrane Capacitive Deionization Using Micropatterned Ion-exchange Membranes, Ionomer Infiltrated Electrodes and Ionomer Coated Nylon Meshes

Membrane capacitive deionization (MCDI) is an emerging water desalination platform that is compact, electrified, and does not require high pressure piping. In this work, we micropatterned highly conductive poly(phenylene alkylene) ion-exchange membranes (IEMs) with different surface geometries for MCDI. The micropatterned membranes increase the interfacial area with the liquid stream leading to a 700 mV reduction in cell voltage when operating at constant current (2 mA cm-2; 2000 ppm NaCl feed) and improved the energy normalized adsorbed salt (ENAS) value, increasing it by 1.4 times. Combining the micropatterned poly(phenylene alkylene) IEMs with poly(phenylene alkylene) ionomer filled electrodes reduced the cell voltage by 1000 mV improved the ENAS values by 2.3 times relative to the base case. This reduction in cell voltage allowed for higher current density operation (i.e., 3 to 4 mA cm-2) without the occurrence of significant parasitic reactions. Finally, we implemented porous ionic conductors into the spacer channel with flat and micropatterned IEM configurations and ionomer infiltrated electrodes. For the configuration with flat IEMs, the porous ionic conductor improved ENAS values across the current density regime (2 to 4 mA cm-2). The porous ionic conductors combined with micropatterned IEMs and porous ionic conductors only improved ENAS when operating the cell at 4 mA cm-2. The latter observation motivates future work to design integrated patterned IEMs with porous ionic conductor materials for improving MCDI energy efficiency over a wide current density range and with varying NaCl feed concentrations.