Ion-Concentration Polarization Regimes for Nanocapillary Array Membranes

Abstract

The current methods for water desalination based on electrical approaches that use membranes for ion filtration can be inefficient in terms of energy efficiency. One reason for energy inefficient desalination is the concentration polarization (CP) region at the membrane solution interface. A better understanding towards CP is essential in improving the process and increasing the efficiency of the membrane separation processes. This work reports on characterization and identification of CP regimes for a potassium phosphate buffer through model nanocapillary array membranes or NCAMs for sub-1V operation conditions. The low operating voltage range is chosen to minimize faradaic reactions and complement other research in the Prakash group towards low-energy consuming water desalination. Three nanopore sizes in NCAMs (10 nm, 50 nm, 100 nm) were used under different bias (10 mV - 750 mV) and concentration (0.2 mM, 1 mM, 10 mM) at pH 7. CP regime is identified and compared to previous reports for CP in membrane system with electrokinetically driven flows. The results indicate that the voltage for onset of the CP regime increases with smaller pore size and lower buffer concentration.