The effect of the flow-regime, reversal of polarization, and oxygen on the long term stability in capacitive de-ionization processes

Abstract

The demand for potable water is continuously increasing. Therefore energy-efficient water desalination methods are the focus of intensive research. Capacitive deionization (CDI) is an energy-efficient water desalination technology. This study focuses on solving the problem of electrode oxidation and degradation in CDI cells. The effect of the geometric flow regime was investigated. Comparison of flow-through vs. flow-by in CDI cells indicates that geometry has an impact on the electro-oxidation rates of the positively polarized electrodes. We examined operation with periodic potential (difference) application by alternating the electrodes polarization. Whilst operating in such a way, the life of CDI cells could be pronouncedly extended without any drops in the desalination level. We investigated the effect of oxygen, which is unavoidably dissolved in the aqueous solutions, on the stability of the electrodes in CDI processes, with the aid of prolonged experiments under nitrogen atmosphere. We determined that the inevitably dissolved air in regular brackish water significantly impacts the oxidation rate of the positively charged electrodes in CDI. Stabilization means for CDI cells are discussed.