Capacitive Deionization of NaCl Solutions at Non-Steady-State Conditions: Inversion Functionality of the Carbon Electrodes

Abstract

In this Article, the consequence of continuous electrochemical oxidation at the positive electrode in an initially symmetrical capacitive deionization (CDI) cell, comprising two identical activated carbon electrodes, is examined and discussed. Extensive and intensive parameters of the CDI cell are defined, and the deviations occurring among them as a result of continuous electrochemical oxidation processes at the positive electrode during prolonged charge–discharge cycling are discussed. A special flow-through CDI cell containing activated carbon fiber (ACF) electrodes was developed for this purpose. Ex situ XPS measurements were conducted to prove the presence of oxidized surface groups on the positive electrode of these cells due to cycling. A surprising phenomenon that looks like an inversion functionality of the carbon electrodes occurring after numerous charge–discharge cycles is observed and explained.

Plasma Treated Active Carbon for Capacitive Deionization of Saline Water

“…The charged ions can be attracted within the electrical double layer formed between the solution and electrode interface. CDI has attracted enormous attention in recent years as an energy saving and environmentally friendly desalination technique, because it can be conducted at ambient conditions and low voltages (<2 V) without secondary waste and does not require high-pressure pumps, membranes, distillation columns, or thermal heaters [3][4][5][6][7][8][9]. It is well known that the ion adsorption capacity of an electrode is directly related to its surface area and bulk conductivity.…”

Poly(arylene ether sulfone) copolymers as binders for capacitive deionization activated carbon electrodes

“…Despite activated carbon being widely studied as a material for CDI electrodes (Bouhadana et al, 2011;Choi, 2010;Hou and Huang, 2013;Hou et al, 2012;Huang et al, 2012;Mossad and Zou, 2012;Porada et al, 2012;Villar et al, 2010;Wang et al, 2012;Wang et al, 2013), one of the drawbacks associated with its use is the requirement for a polymeric binder. Typically hydrophobic polymers such as poly(tetrafluoroethylene) (PTFE) (Chang et al, 2012;Lee et al, 2009) or poly(vinylidene fluoride) (PVDF) (Zhang et al, 2012) are used to bind activated carbon powder.…”

Effect of pH waves on capacitive charging in microfluidic flow channels

“…It has been shown previously that these pH waves can severely hinder the electrokinetic remediation of e.g., soils [24] or porous building materials [25]. The origin of pH variations arising in electrolytes is often related to Faradaic electrode reactions [26][27][28], whereas capacitive-induced pH variations due to locally released protons from a silicon nitride wall have been observed as well [29]. Consequently, the formation of acidic and alkaline regions is a surface effect that is largely enhanced in the flow channel of CDI systems due to their large electrode surface area relative to the volume of the flow channel [30].…”