Jaehan Lee

Hybrid capacitive deionization to enhance the desalination performance of capacitive techniques

Based on a porous carbon electrode, capacitive deionization (CDI) is a promising desalination technology in which ions are harvested and stored in an electrical double layer. However, the ion removal capacity of CDI systems is not sufficient for desalting high-concentration saline water. Here, we report a novel desalination technique referred to as “hybrid capacitive deionization (HCDI)”, which combines CDI with a battery system. HCDI consists of a sodium manganese oxide (Na4Mn9O18) electrode, an anion exchange membrane, and a porous carbon electrode. In this system, sodium ions are captured by the chemical reaction in the Na4Mn9O18 electrode, whereas chloride ions are adsorbed on the surface of the activated carbon electrode during the desalination process. HCDI exhibited more than double the ion removal sorption capacity (31.2 mg g−1) than a typical CDI system (13.5 mg g−1). Moreover, it was found that the system has a rapid ion removal rate and excellent stability in an aqueous sodium chloride solution. These results thus suggest that the HCDI system could be a feasible method for desalting a highly concentrated sodium chloride solution in capacitive techniques.

Capacitive and Oxidant Generating Properties of Black-Colored TiO2 Nanotube Array Fabricated by Electrochemical Self-Doping

Recently, black-colored TiO2 NTA (denoted as black TiO2 NTA) fabricated by self-doping of TiO2 NTA with the amorphous phase led to significant success as a visible-light-active photocatalyst. This enhanced photocatalytic activity is largely attributed to a higher charge carrier density as an effect of electrochemical self-doping resulting in a higher optical absorbance and lower transport resistance. Nevertheless, the potential of black TiO2 NTA for other electrochemical applications, such as a supercapacitor and an oxidant-generating anode, has not been fully investigated. Here, we report the capacitive and oxidant generating properties of black TiO2 NTA. The black TiO2 NTA exhibited significantly a high value for areal capacitance with a good rate capability and novel electrocatalytic activity in generating (•)OHs and Cl2 compared to pristine TiO2 NTA with the anatase phase. This study suggests that the black TiO2 NTA be applied as a supercapacitor and an oxidant generating anode.

Lithium recovery from brine using a λ-MnO2/activated carbon hybrid supercapacitor system.

Lithium is one of the most important elements in various fields including energy storage, medicine manufacturing and the glass industry, and demands for lithium are constantly increasing these days. The lime soda evaporation process using brine lake water is the major extraction method for lithium, but this process is not only inefficient and time-consuming but also causes a few environmental problems. Electrochemical recovery processes of lithium ions have been proposed recently, but the better idea for the silver negative electrodes used in these systems is required to reduce its cost or increase long term stability. Here, we report an electrochemical lithium recovery method based on a λ-MnO2/activated carbon hybrid supercapacitor system. In this system, lithium ions and counter anions are effectively captured at each electrode with low energy consumption in a salt solution containing various cationic species or simulated Salar de Atacama brine lake water in Chile. Furthermore, we designed this system as a flow process for practical applications. By experimental analyses, we confirmed that this system has high selectivity and long-term stability, with its performance being retained even after repetitive captures and releases of lithium ions.

Rocking Chair Desalination Battery Based on Prussian Blue Electrodes

The demand for fresh water has been increasing, caused by the growing population and industrialization throughout the world. In this study, we report a capacitive-based desalination system using Prussian blue materials in a rocking chair desalination battery, which is composed of sodium nickel hexacyanoferrate (NaNiHCF) and sodium iron HCF (NaFeHCF) electrodes. In this system, ions are removed not only by charging steps but also by discharging steps, and it is possible to treat actual seawater with this system because the Prussian blue material has a high charge capacity with a reversible reaction of alkaline cations. Here, we demonstrate a rocking chair desalination battery to desalt seawater, and the results show that this system has a high desalination capacity (59.9 mg/g) with efficient energy consumption (0.34 Wh/L for 40% Na ion removal efficiency).

Electrochemical selective ion separation in capacitive deionization with sodium manganese oxide

Electrochemical selective ion separation via capacitive deionization, for example, separation of lithium resource from brine, using lithium ion batteries is proposed and demonstrated to have the potential for separating specific ions selectively from a solution containing diverse ions. This separation method is of great industrial concern because of applicability in various fields such as deionization, water softening, purification, heavy metal removal, and resource recovery. Nevertheless, besides the selectivity of materials for lithium ion batteries toward Li+, there is very little investigation on the selectivity of the materials for sodium ion batteries toward Na+. Here, the electrochemical selectivity of sodium manganese oxide (Na0.44MnO2), one of the most widely used material in sodium ion batteries, for Na+ and other cations (K+, Mg2+, and Ca2+) is investigated. Selective Na+ separation using the system consisting of Na0.44MnO2 and a Ag/AgCl electrode is successfully demonstrated from a solution containing diverse cations (Na+, K+, Mg2+, and Ca2+) via a two-step process that involves a capturing step (charging process) and a releasing step (discharging process). The results showed that Na0.44-xMnO2 has over 13 times higher selectivity for Na+ than for K+ and 6-8times higher selectivity for Na+ than for Mg2+ and Ca2+ in the electrolyte containing equal concentrations of the respective ions. Additionally, as a practical demonstration, Na+ was successfully separated from an industrial raw material used for pure KOH production (estimated ratio of Na+:K+=1:200).

Electrochemical softening using capacitive deionization (CDI) with zeolite modified carbon electrode (ZMCE)

AbstractDivalent ions such as calcium and magnesium ions are thought to cause hardness in water inducing scale problems in the pipelines of boilers and heat exchangers. Thus, water softening has gained wide interest in water treatment technology. Although zeolite particles have been widely used as a material for the removal of divalent ions, its low ion-exchange efficiency based on diffusion-dependent process has limited their applications in water softening. Herein, we report effective electrochemical softening using zeolite with capacitive deionization (CDI), which is a desalination technology with electrochemical ad/desorption in an electric double layer. The carbon electrode with zeolite (denoted as a zeolite modified carbon electrode (ZMCE)) was prepared by the slurry and pasting method with zeolite particles and carbon black. ZMCE exhibited a significantly enhanced efficiency in the removal of divalent ions in softening using the CDI process compared to the normal softening process based on diffusio...

Electrochemical lithium recovery and organic pollutant removal from industrial wastewater of a battery recycling plant

Lithium has become one of the most important elements due to the rapid development of mobile devices and electronics lately. There has been a steep increase in the global demand for lithium, and developing an economic supply of lithium is thereby important for battery industries. This study presents a new method for recovering lithium in wastewater from battery recycling plants, in which a considerable amount of lithium (∼1900 mg L−1) is discarded. There was a significant amount of organic pollutants present in the wastewater (∼300 mg L−1 of dissolved organic carbon), and so to resolve this, we proposed an electrochemical system containing a lithium-recovering electrode (lithium manganese oxide, LMO) and an oxidant-generating electrode (boron-doped diamond, BDD) to simultaneously recover lithium and decompose organic pollutants. Repeated operation of the electrochemical system demonstrated highly efficient and reliable lithium extraction and organic material removal from wastewater. After the lithium recovery system operation, a lithium-rich solution (98.6 mol% lithium among cations) was obtained, and the organic pollutants in the wastewater decreased by 65%. Furthermore, the electrochemical behavior of LMO and BDD was investigated under various operating conditions to provide useful insights into the industrial applications of our LMO/BDD system.

Corrigendum: Extraction of Salinity-Gradient Energy by a Hybrid Capacitive-Mixing System

Figure 5 Change in the energy and power density production of the hybrid Capmix on varying the applied current from 1 to 4 mA with a total charge of 0.24 C; correct secondary y-axis. The authors and the editorial office apologize for this oversight and for any inconvenience caused. J. Lee, H. Yoon, J. Lee, T. Kim, J. Yoon* Extraction of Salinity-Gradient Energy by a Hybrid Capacitive-Mixing System ChemSusChem 2017, 10, 1600–1606 DOI: 10.1002/cssc.201601656