Dual-ions electrochemical deionization: a desalination generator

Abstract

Seawater desalination is a leading method for tackling the challenge of global freshwater shortage. However, existing desalination technologies like capacitive deionization (CDI) have their own limits, including high energy consumption or low ion removal capacity, which is not sufficient for desalting high-concentration saline water with low cost. Herein, we present a concept of flow dual-ions electrochemical deionization technology, which consists of BiOCl for chloride ion Faradaic electrode on the negative side, sodium manganese oxide (Na_0.44MnO₂) as sodium ion Faradaic electrode on the positive side, and a flow salt feed as electrolyte. It utilizes a redox reaction to individually capture chloride ions and sodium ions concurrently. Under positive electric current operations, the two ions are released for NaCl water electrolyte to flow. On switching to negative electric current, the chloride ions are extracted into the negative electrode, and thus prevented from flowing into the NaCl solution while sodium ions are electrochemically captured into the positive electrode. The novel dual-ions in Faradaic deionization deliver a stable and reversible salt removal/release capacity of 68.5 mg g⁻¹ when operated at a current density 100 mA g⁻¹, which indicates an amount over twice the salt absorption amount of the previously reported best performance (31.2 mg g⁻¹) obtained by a hybrid capacitive deionization system. The electric charge efficiency is up to 0.977 during salt desorption process and 0.958 during absorption process. Owing to the salt removal, energy will be released during discharge process; therefore, the current system is called “desalination generator”. Our research will supply a new method for desalination flow-through system.