Cation-Exchange Membrane with Low Frictional Coefficient and High Limiting Current Density for Energy-Efficient Water Desalination

A sulfonated poly(ether ether ketone) (SPEEK) and phosphorylated graphene oxide (PGO) composite of a cation-exchange membrane with low frictional coefficient and high limiting current density has been reported for water desalination by rapid electrodialysis. The incorporation of PGO in the membrane matrix showed a significant impact on the macroscopic properties, counterion frictional coefficient, and performance of the membrane. A well-optimized SPEEK/PGO-8 (8% PGO content, w/w) membrane showed improved conductivity (4.15 × 10 -2 S cm -1 ) and permselectivity (87%), and excellent stabilities (thermal, mechanical, and chemical) because of cherished polymer-PGO (filler) interaction via H-bonding. The efficiency of the SPEEK/PGO-8 membrane was also evaluated for the desalination of brackish water near limiting current density ( I lim ). Ion concentration polarization (ICP) was assessed by i - V curves, and below I lim , water splitting or change in product water pH was ruled out. While above I lim (10.5 mA cm -2 ), ICP was significant and could be finally tuned with applied current density for producing desalinated water with a desired pH. Furthermore, improved I lim , high current efficiency (82.9%), and low energy consumption (7.9 kWh kg -1 of the salt removed) of the SPEEK/PGO-8 membrane during electrodialysis provide a broad current window for efficient and rapid water desalination/purification.