(222c) Design Rules for Generating Acid and Base from Membrane-Free Electrolysis of Brine

As water scarcity issues become exacerbated by climate change and population growth, an evident solution is to enlarge potable water production via desalinization. Unfortunately, this technology leads to major environmental side effects that result from the discharge of concentrated seawater (reject brine) into neighboring bodies of seawater, land, or evaporation ponds. The long-term impact of this practice on marine life is still unknown, but the brine's high temperature and salinity levels could be devastating. On the other hand, reject brine contains minerals and salts like calcium, magnesium, and sodium chloride that can be harvested and reutilized by other industries. A promising approach to treat reject brine is to use membraneless electrolyzers, which are well-suited for operation with highly conductive liquid electrolytes and avoid the need for membranes by controlling fluid flow to separate anode and cathode products before they can cross over to opposing effluent streams. They can operate in a wide range of pH environments and simultaneously generate acid and base; however, the lack of separator can result in high levels of product crossover if the electrolyzer is not designed or operated properly. This issue can be addressed by operating at higher flow rates, which can push bubbles away from the centerline separating the two electrodes, thereby minimizing crossover. However, higher flow rates also dilute the generated product. In this study, we investigate the trade-offs between crossover, cell voltage, and the concentration of generated acid and base with a combination of electroanalytical measurements, in situ high-speed videography, pH dye experiments, and modeling. Additionally, the distribution of catalysts was varied to control where the product was generated and further reduce crossover. Our study demonstrates that placing the active catalyst in the opposite face of the electrodes increases current utilization by up to 40% and improves catalyst stability. Further work involves the scale-up and optimization of the reactor design.