Increasing the Electrolyte Salinity to Improve the Performance of Anion Exchange Membrane Water Electrolyzers

Direct operation of anion exchange membrane water electrolyzers(AEMWEs) with near-neutral pH feeds avoids the use of highly alkalineand corrosive solutions. However, using neutral pH solutions currentlyfaces fundamental operational challenges that diminish performanceand reduce long-term stability due to poor solution conductivity andlow hydroxide ion concentration. Here, we showed that amending near-neutralpH solutions with low concentrations of alkali metal salts in a dry-cathodeconfiguration substantially improved performance and stability. AddingNaClO(4) (10 mM) to the anolyte reduced the operating voltageby 0.19 to 2.58 V at 500 mA/cm(2) compared to non-salinesolutions (2.77 V). However, further increases in the feed salt concentration(100 mM NaClO4) reduced performance (2.64 V) due to a greaterco-ion diffusion through the anion exchange membrane. Electrolyzerperformance was further improved by utilizing salts with high conductivitysuch as KNO3. Using a saline anolyte reduced ohmic resistance,resulting in smaller applied voltage and energy consumption for hydrogengeneration, while the combined effect of the membrane charge and theelectric field direction in the dry-cathode feed configuration minimizedion crossover. Thus, increasing the salinity of near-neutral pH solutionsrepresents a cost-effective strategy to improve the performance ofAEMWE compared to ultrapure electrolytes, minimizing risks and costsassociated with recirculating highly alkaline solutions.