Long term stability of capacitive de-ionization processes for water desalination: The challenge of positive electrodes corrosion

Corrosion of the positive electrodes, in capacitive deionization (CDI) cells for water desalination processes, is a major problem that may prevent them from becoming practically important. This paper deals with the consequence of the corrosion of the positive electrodes in CDI processes on the desalination performance, in terms of capacity and the ratio between adsorption of counter-ions and desorption of co-ions. The detrimental effect of the positive electrodes oxidation on the de-ionization efficiency is demonstrated and discussed. The role of the potential difference applied to CDI cells on the electrodes' stability was explored as well. We used for this study CDI cells comprising several pairs of activated carbon electrodes and 3 electrodes cells containing reference electrode. The interrelated parameters measured included potential, current, concentration (translated from conductivity measurements) and pH vs. time. The present study and the understanding gained herein, will enable the development of durable, long term and effective CDI processes.