A highly efficient faradaic desalination system utilizing MnO2 and polypyrrole-coated titanium electrodes

Abstract

A highly efficient pseudocapacitive desalination system is constructed with positive MnO2 and negative polypyrrole electrodes. Both materials deposited by electrochemical methods exhibit faradaic reactions with the “memory effect” and permit the unique multi-function application with salt-removing and concentrating abilities. The quasi-steady state electrode potentials of both electrodes under charged/discharged states and the cell salt removal capacity (SRC) highly depends on the mass loading of active materials. To ensure the quasi-steady state electrode potentials of materials in their working potential windows, the mass loadings of active materials are carefully controlled by the deposition charge density. After the mass loading adjustment, SRC reaches 78 mg g−1 in a 60-min salt-removing process. The salt removal rate (SRR) reaches the highest value of ca. 5 mg g−1 min−1 during the initial 5 min and continuously decreases to near 0 with prolonging the desalination time. In the stability test, this MnO2//PPy cell remains over 90% of its original SRC in a 100-cycle test. Shortening the time of a single operation segment is an efficient way to increase the average SRR which reaches 212.7 mg g−1 in this MnO2//PPy cell transferring NaCl from one solution to another in a 120-min test using the 4/4-min model.