A Redox-Shuttled Electrochemical Method for Energy-Efficient Separation of Salt from Water

We present a novel electrochemical method for separating salt from water in a practical, energy-efficient manner: SUPER (ShUttle-Promoted Electrolyte Removal). SUPER combines elements from redox flow batteries and conventional electrodialysis: a redox shuttle in a four-chambered cell architecture drives ion motion at very low voltages and energy consumption without splitting water, uses no electrocatalysts, and can be salt-agnostic. As exemplified by NaCl, we demonstrate salt removal at a gravimetric specific energy consumption (SEC) as low as 0.046 kWh/kg NaCl transported, which is equivalent to producing water at drinkable salinity (<0.5 parts per thousand [ppt] NaCl) at a volumetric SEC of 1.58 kWh/m3 in the absence of electroosmotic or osmotic losses. When operating at reasonably high current densities and accounting for these losses, we demonstrate extensive single-stage desalination of simulated seawater (35 → 0.192 ppt NaCl) at a volumetric SEC of 4.91 kWh/m3, as well as complete desalination of concentrated brine (203.8 → 0.192 ppt NaCl) over seven stages at a specific energy consumption of 84.37 kWh/m3. In addition to its use in seawater desalination, SUPER is capable of efficiently desalting concentrated brines that are not currently possible to treat with nonthermal methods.