Enhanced desalination efficiency in modified membrane capacitive deionization by introducing ion-exchange polymers in carbon nanotubes electrodes

A modified membrane capacitive deionization (m-MCDI) device was proposed with high desalination efficiency. The m-MCDI electrodes were fabricated by introducing the anion exchange polymer (dimethyl diallyl ammonium chloride) and cation exchange (polyethyleneimine) polymer into carbon nanotubes (CNTs) electrodes and their desalination performance in NaCl solutions was investigated. The m-MCDI unit cell based on both anion and cation exchange polymers exhibits a high NaCl removal of 93%, much higher than that of conventional capacitive deionization cell with CNTs electrode (25%) or MCDI cell with commercial anion and cation exchange membranes (74%) in a certain experiment at 1.2 V and for an initial conductivity of 50 μS/cm. The large improvement in desalination performance is mainly due to the reduced co-ion expulsion effect by introducing ion exchange polymers and the better contact adhesion between ion exchange polymers and electrodes than between commercial ion exchange membranes and electrodes.