Integrated electrostatic exclusion and electrosorption in a tubular nanoporous membrane cathode with an internal packed bed for simultaneous removal of cations and anions

Nanofiltration membranes are efficient for desalination but are limited by concentration polarization. We report an integrated electrochemical reactor comprising a tubular nanoporous carbon membrane (CM) and an internal activated carbon packed bed reactor (PBR) that simultaneously achieves co-ion exclusion and counter-ion electrosorption under a single applied cathodic potential. The system achieves Na 2 SO 4 rejection above 99% at an inlet concentration of 500 mg L −1 under −0.4 V vs. SCE, and maintains rejection above 90% over 30 charge-discharge cycles. The 5.6 nm pore geometry of the CM concentrates the local electric field at the pore entrance, imposing strong Donnan repulsion against co-ions (SO 4 2− , Cl − ). The same cathodic field activates electrosorption of counter-ions (Na + , Ca 2+ ) across both the CM pore wall and the PBR, where the high specific surface area of activated carbon provides abundant adsorption sites. The integrated tubular configuration ensures that anions and cations are simultaneously removed within a single cathodic compartment. Finite element analysis confirms that SO 4 2− rejection is completed within 1.5 nm of the channel entrance, while Na + electrosorption extends across the CM pore wall. This dual-mechanism strategy under a single electric field offers a scalable platform.