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 (Ilim). Ion concentration polarization (ICP) was assessed by i–V curves, and below Ilim, water splitting or change in product water pH was ruled out. While above Ilim (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 Ilim, 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.