Mitigating Water Crossover by Crosslinked Coating of Cation‐Exchange Membranes for Brine Concentration

Abstract Undesired water crossover through ion‐exchange membranes is a significant limitation in electrically driven desalination processes. The effect of mitigating water crossover is twofold: 1) The desalination degree is less reduced due to the unwanted removal of water, and 2) the brine concentration is increased due to decreased dilution by an unwanted crossover of water molecules. Hence, water crossover limits the desalination and concentration efficiency of the processes, while the energy demand to achieve a certain level of desalination or concentration increases. This effect is especially pronounced when treating high salinity solutions, which goes hand in hand with the crossover of many ions through the ion‐exchange membranes. A crosslinked coating for cation‐exchange membranes (CEMs) is presented in this work, which can significantly mitigate such undesired water crossover. The efficacy is demonstrated using the flow‐electrode capacitive deionization process applied for desalination and concentration of saline brines at feed concentrations of 60 and 120 g L⁻¹ NaCl. With just a single coated CEM, the water crossover was reduced by up to 54%.