Capacitive desalination of ZnO/activated carbon asymmetric capacitor and mechanism analysis

Capacitive deionization with asymmetric electrodes: Electrode capacitance vs electrode surface area

“…These imbalances have been used to selectively remove ions from solution [21,[28][29][30], but could adversely affect the equilibrium salt adsorption capacity of a CDI cell. A recent study reported that the effect of asymmetry in anode and cathode geometric ratios (where anode was 2x and 3x times larger than the cathode and vice-versa) led to an increased salt adsorption capacity, which was stated to be dependent on ionic sizes and governed by the requirement to maintain charge neutrality in solution.…”

“…Given the difficulty in standardizing the electrode properties which are synthesis/fabrication process dependent, there will always be an inherent in-homogeneity between the anode and cathode surface properties of a CDI cell. This in-homogeneity gets expressed in terms of electrode resistivity [19], surface charges [20][21][22][23][24][25] or available active area [26,27] etc. leading to unequal distribution of potential between the anode and the cathode.…”

“…If the total capacitance is indeed limited by the lower capacitance, it is expected that the present configuration will highlight the phenomenon due to acute asymmetry in the electrode capacitance. It is to be noted that both ZnO coated ACC and uncoated ACC were preferentially incorporated as the cathode in the asymmetric cells using graphite as the anode [21,41].…”

Desalination with porous electrodes : Mechanisms of ion transport and adsorption

“…• reduce charge and energy efficiency of the process (electrons involved in faradaic reactions do not contribute to ion adsorption in EDLs); • can result in unwanted pH changes of the effluent solution, as some reactions involve the production or consumption of protons or hydroxyl ions, which can result in precipitation of salt on membranes or into electrodes, and thereby affect the long-term stability of the cell [64,[66][67][68]; • can result in oxidation of carbon -often the main electrode material in CDI -and thereby also affect the stability of the CDI desalination process [63][64][65].…”

“…These pH changes can result in precipitation and scaling of membranes and electrodes, and can affect long-term stability of membrane and electrode materials [64,[66][67][68]. Also, these pH changes can lead to a product that has an undesired pH.…”