Effect of a semiconductor dielectric coating on the salt adsorption capacity of a porous electrode in a capacitive deionization cell

A theoretical model was developed to study the effect of an additional dielectric coating on the conducting electrodes in a capacitive deionization cell. The electric field generated at the electrode surface and its distribution was quantitatively investigated for coating materials with different dielectric properties. The model shows that a nanostructured low dielectric and intrinsically polar material like zinc oxide (ZnO) is well suited to enhance the efficiency of capacitive desalination. Electrodes formed by ZnO nanorods coated on conducting electrodes of activated carbon cloth (ACC) were subsequently fabricated and its desalination parameters were studied using a 17 mM (1000 ppm) NaCl solution as the feed at an applied potential of 1.6 V DC. The composite ZnO nanorod coated electrodes improved salt removal efficiency by 40%, and adsorbed 35% of the salt in a single pass experiment, at a charge efficiency of 80% and an electrosorptive capacity of 8.1 mg/g of the electrode. A simultaneous increase in the ion adsorption rate led to a ∼40% reduction in the energy consumption as compared to an uncoated ACC electrode.