2.2.4 Faradaic Reaction
In CDI process there are two reactions that might be happens, Faradaic reactions and non-Faradaic reactions. Ion transport and capacitive storage are categorized as non-Faradaic reaction which is standard process that hopefully happen in CDI process, while Faradaic reaction (i.e, redox reactions both on the surface of and within the carbon electrodes) may lead to the formation of chemical byproducts and/or pH fluctuations of the produced water [44], [45]. Faradaic reaction also could lead to instability of long cycle CDI performance, which is specifically caused by reduction reaction at the cathode which is automatically drive the anode potential to possible values where oxidation in anode is occurred [46].
He et al,.[47] studied about Faradaic reaction in CDI process which they found that there was a possibility of pH fluctuations and H2O2 generation in sample solution. pH fluctuations are considered as important issue since it could affect the water quality and might lead to carbonate scaling which could harm the pipes or the system itself. The severity of issue is increasing related to operating potential in CDI system. A decrease of pH was recorded when the 1.2 V and 1.5 V (High potential) were charged in the system, implying that porous carbon oxidation may have occurred. The reaction of Carbon electrode oxidation can be viewed in Equation 3.
The problems caused by Faradaic reaction might have benefits in advanced water treatment application.