Water desalination with nickel hexacyanoferrate electrodes in capacitive deionization: Experiment, model and comparison with carbon

Abstract

Capacitive deionization (CDI) is a water desalination technology in which ions are removed from water by creating a potential difference between two capacitive electrodes. Porous carbon has been extensively used as an electrode material in CDI. However, recent developments in the field of intercalation materials have led to their application in CDI due to their large ion storage capacity. One such intercalation material, nickel hexacyanoferrate (NiHCF), was used in this study as the electrode material. A symmetrical cell was assembled with two identical NiHCF electrodes separated by an anion-exchange membrane. The effect of operational parameters such as current density, feed concentration and flow rate on the desalination characteristics of the cell was investigated. The highest salt adsorption capacity of ≈ 35 mg/g was measured at a current density of 2.5 A/m2 in a 20 mM NaCl feed solution. Furthermore, a Nernst-Planck transport model was successfully used to predict the change in the outlet concentration and cell voltage of the symmetric CDI cell. Finally, performance of the symmetric NiHCF CDI cell was compared with an MCDI cell with porous carbon electrodes. The NiHCF cell, on average, consumed 2.5 times less energy than the carbon-based MCDI cell to achieve similar levels of salt removal from saline water in CDI.