Enhancement in Ion Adsorption Rate and Desalination Efficiency in a Capacitive Deionization Cell through Improved Electric Field Distribution Using Electrodes Composed of Activated Carbon Cloth Coated with Zinc Oxide Nanorods

Abstract

Electrodes composed of activated carbon cloth (ACC) coated with zinc oxide (ZnO) nanorods are compared with plain ACC electrodes, with respect to their desalination efficiency of a 17 mM NaCl solution at different applied potentials. Polarization of the ZnO nanorods increased the penetration depth and strength of the electric field between the electrodes, leading to an increase in the capacitance and charge efficiency at reduced input charge ratios. Uniform distribution of the electric field lines between two electrodes coated with ZnO nanorods led to faster ion adsorption rates, reduced the electrode saturation time, and increased the average desalination efficiency by ∼45% for all applied potentials. The electrodes were characterized for active surface area, capacitance from cyclic voltammetry, theoretical assessment of surface area utilization, and the magnitude of electric field force acting on an ion of unit charge for each potential.

Desalination and disinfection of inland brackish ground water in a capacitive deionization cell using nanoporous activated carbon cloth electrodes

“…Upon increasing the scan rate to 50 mV/s, capacitance reduced to 40 F/g (Fig. 1b), attributed to reduced time available for ion adsorption along with a denser mass transfer at the electrode-electrolyte interface leading to overlapping double layers at pore entrances [11,15]. The large capacitance values correspond well with the porous structure of ACC, giving it an active specific surface area (SSA) of~1000 m 2 /g (as measured from NMR experiments), which is comparable to SSA of activated carbon powders and other traditionally used electrode materials [18,43,44].…”

“…4b). At a given rate of change of potential, a reduction in the peak inrush current indicates a reduced capacitance [15], attributed to clogging of the electrode pores by organic contaminants in well water leading to a reduction in the total salt adsorption capacity. On a positive note, the lower current led to a reduction in the power consumption per m 3 of desalted water from 0.85 kWh for synthetic water to 0.78 kWh for well water (Table 1).…”

“…New stand-alone desalting techniques like capacitive deionization (CDI) have addressed the issue by specifically operating in the brackish water salt regimes [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], which are predicted to be present even offshore beneath the continental shelf [21]. CDI involves the potential mediated separation of salt from water, rather than water from salt, as practiced in traditional desalting techniques like RO and MSF [22,23].…”

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

“…Water to be desalinated passes between or across the electrodes [6] and is desalted by the potential mediated adsorption of ions onto the electrode surfaces [9][10][11][12][13][14][15]. Prior research has shown that the capacity of adsorbed ions and their adsorption rate is linked to the strength and distribution of localized electric field produced at the electrode surfaces [7,10,[16][17][18], which in turn is governed by the electrical properties of the electrode [10,16,19]. 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.…”

Desalination with porous electrodes : Mechanisms of ion transport and adsorption

“…Alternative designs use carbon electrode wires [80], flowable electrode slurries [7,[72][73][74]76] or flow-through electrodes [112]. In addition, electrodes can be chemically modified [88,113], nanoparticles can be incorporated [114][115][116], ion-selective coatings can be applied [117,118], or ionexchange membranes can be placed in front of the electrodes in a modification called Membrane Capacitive Deionization, or MCDI [27,28,35,71,102,[119][120][121].…”