Dong Kook Kim

Desalination via a new membrane capacitive deionization process utilizing flow-electrodes

A capacitive deionization process utilizing flow-electrodes (FCDI) was designed and evaluated for use in seawater desalination. The FCDI cell exhibited excellent removal efficiency (95%) with respect to an aqueous NaCl solution (salt concentration: 32.1 g L−1), demonstrating that the FCDI process could effectively overcome the limitations of typical CDI processes.

Ion storage and energy recovery of a flow-electrode capacitive deionization process

The ion storage and extraction (or the ion charge and discharge) of a continuous capacitive deionization system were investigated using novel flow-electrode capacitive deionization (FCDI). The flow-electrode, charged by constant voltage, generated about 20% of the supplied energy in an FCDI cell during constant current discharge with NaCl solution (concentration: 35.0 g L−1).

Flow-Electrode Capacitive Deionization Using an Aqueous Electrolyte with a High Salt Concentration

Flow-electrode capacitive deionization (FCDI) is novel capacitive deionization (CDI) technology that exhibits continuous deionization and a high desalting efficiency. A flow-electrode with high capacitance and low resistance is required for achieving an efficient FCDI system with low energy consumption. For developing high-performance flow-electrode, studies should be conducted considering porous materials, conductive additives, and electrolytes constituting the flow-electrode. Here, we evaluated the desalting performances of flow-electrodes with spherical activated carbon and aqueous electrolytes containing various concentrations of NaCl in the FCDI unit cell for confirming the effect of salt concentration on the electrolyte of a flow-electrode on desalting efficiency. We verified the necessity of a moderate amount of salt in the flow-electrode for compensating for the reduction in the performance of the flow-electrode, attributed to the resistance of water used as the electrolyte. Simultaneously, we confirmed the potential use of salt water with a high salt concentration, such as seawater, as an aqueous electrolyte for the flow-electrode.

Surface-modified spherical activated carbon for high carbon loading and its desalting performance in flow-electrode capacitive deionization

We have synthesized a new type of activated carbon (AC) containing ion-selective functional groups, trimethylammonium (AC-N) for anodes and sulfonate (AC-S) for cathodes, for high carbon loading of flow-electrodes. The AC-N and AC-S were partially covered with a 50 nm-thick polymer layer and their surfaces became more hydrophilic than that of bare AC. In the case of bare AC, the maximum carbon concentration in the flow electrodes was 10%, while in the case of the surface-modified AC (AC-N and AC-S), it increased to a maximum of 35% and decreased the viscosity due to the electrostatic repulsion. Moreover, with the increase in carbon concentration, the salt removal efficiencies were improved from 8.2% to 27.7%. This increase in efficiency was attributed to the formation of percolating networks, which occurred because of high carbon loading. The resulting improvement in electronic conductivity at higher loading led to a higher current, and thus an improved salt removal efficiency. Therefore, we expect that the surface-modified AC electrode can be used as a dispersant for hydrophobic AC particles in aqueous solution, as well as in flow electrodes to improve desalting performance in FCDI systems.

A novel three-dimensional desalination system utilizing honeycomb-shaped lattice structures for flow-electrode capacitive deionization

A highly compact and scalable three-dimensional desalination cell was realized by utilizing honeycomb-shaped porous lattice scaffolds. It did not require a free-standing ion exchange membrane and a thick current collector. Furthermore, the porous structure can act as a structural scaffold. Therefore, it can be readily scaled-up in three dimensions allowing enhanced salt removal capacity. This provides great potential for scale-up and commercialization of desalination using the capacitive deionization technology.