Carbon Black Flow Electrode Enhanced Electrochemical Desalination Using Single-Cycle Operation

Abstract

Flow-electrode electrochemical desalination (FEED) processes (e.g., flow-electrode capacitive deionization), which use flowable carbon particles as the electrodes, have attracted increasing attention, holding the promise for continuous desalination and high desalting efficiency. While it is generally believed that carbon particles with abundant microporous and large specific capacitances (e.g., activated carbon, AC) should be ideal candidates for FEED electrodes, we provide evidence to the contrary, showing that highly conductive electrodes with low specific surface area can outperform microporous AC-based electrodes. This study revealed that FEED using solely high surface area AC particles (∼2000 m 2 g −1 , specific capacitance of ∼44 F g −1 , average salt adsorption rate of ∼0.15 μmol cm −2 min −1 ) was vastly outperformed by electrodes based solely on low-surface area carbon black (CB, ∼70 m 2 g −1 , ∼0.5 F g −1 , ∼0.75 μmol cm −2 min −1 ). Electrochemical impedance spectroscopy results suggest that the electrode formed by CB particles led to more effective electronic charge percolation, likely contributing to the improved desalination performance. In addition, we propose and demonstrate a novel operation mode, termed single cycle (SC), which greatly simplified the FEED cell configuration and enabled simultaneous charging and discharging. Using SC mode with CB flow electrodes delivered an increased average salt removal rate relative to the more traditional short-circuited closed cycle (SCC) mode, achieving up to 1.13 μmol cm −2 min −1 . Further investigations demonstrate that up to 50% of energy input would be avoided when using CB flow electrodes operated under SC mode as compared to that of AC flow electrodes operated under SCC mode. In summary, the FEED process presented in this study provided an innovative and promising approach toward high-efficient and low-cost brackish water desalination.

On the Resistances of a Slurry Electrode Vanadium Redox Flow Battery

“…Electrical conductivity depends on the contact area between these particles, which is mainly limited by the shape. One possible approach is to use a conductive additive within the slurry electrodes to increase the conductivity . In this work, we used KB nanoparticles as conductive additive for the GP slurries.…”

Electrochemically mediated deionization: a review

“…84 By sacrificing SAC for electrical conductivity (using only carbon black as the electrode material) a recent study demonstrated enhanced ASAR, scaled by the membrane area, by a factor of five. 78 Consequently, the total salt removal increased without any decrease in energy efficiency. The absolute value of energy efficiency reported in this same study, ∼8 μmol J −1 , is on the same order of magnitude as that of a standard MCDI system, 41 but we remind the reader that such comparisons are complicated by variation of experimental conditions (see section on CDI metrics).…”

“…In this work, the electrodes are cycled from one half-cell to the other to allow continuous reuse of the active material. 78 Reproduced with permission from ref. 78.…”

Flow Electrode Capacitive Deionization (FCDI): Recent Developments, Environmental Applications, and Future Perspectives

“…The first FCDI device with three chambers (i.e., one spacer and two electrode chambers) was designed and experimentally tested for seawater desalination by Jeon and co-workers in Korea in 2013 (Figure a) . The following years have witnessed a dramatic increase in the number of trials conducted to enhance the desalination performance by optimizing cell configuration and components, − as well as operational modes (Figure b). , While desalination is the dominant application area for FCDI, there is an increasing number of studies related to resource recovery and contaminant abatement. − …”