A high-capacity hybrid desalination system using battery type and pseudocapacitive type electrodes

Abstract

A membrane-free hybrid system employing the battery-type copper hexacyano-ferrate (CuHCF) and the pseudocapacitive polypyrrole (PPy) as the positive and negative electrodes are designed for faradaic desalination. Both materials exhibit a memory effect, a unique characteristic of the faradaic reaction, with the dual function of ion removing and concentrating. The appropriate mass ratio of two materials is adjusted according to the positive/negative charge balance to ensure that both electrodes work in their respectively suitable potential windows. Through the little inverted voltage (−0.2 V) during the discharge process in order to keep the two electrodes in the desirable potential windows in comparison with the case discharged at 0 V, the salt removal capacity (SRC) of this hybrid system is significantly increased from 21.17 mg g−1 to 26.62 mg g−1 in 8 mM NaCl. Under this operation condition, the cell keeps >90 % of the original SRC in a 100-cycle stability test. The SRC obtained in 8 mM NaCl solution can increase to 38.64 mg g−1 after employing the acid-treated CNT/CuHCF composite. The system also exhibits superior performance on removing other cations including K+, Mg2+, and Ca2+. All results reveal the promising application potential of this system to the faradaic desalination and metal-ion concentrating and recovering.