Optimization on electrode assemblies based on ion-doped polypyrrole/carbon nanotube composite in capacitive deionization process

• PPy/CNT doped with DBS− and Cl− were prepared and used in CDI electrodes.
• Low charging resistance of PPy-DBS/CNT and PPy-Cl/CNT electrodes was obtained.
• High electrosorption capacity of CDI cell was achieved by PPy/CNT electrodes

The composites of carbon nanotube (CNT) and the conducting polymer polypyrrole (PPy) doped with dodecyl benzene sulfonate (DBS−) and Cl− were prepared respectively by chemical oxidation method and made into two types of composite electrode (PPy-DBS/CNT and PPy-Cl/CNT) for capacitive deionization (CDI) cell. Enhanced electrochemical performance of the composite electrodes was confirmed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) test. The results of CV showed that the specific capacitance of PPy/CNT doped with either DBS− or Cl− was about 2.3–2.5 times that of the CNT electrode. And EIS test demonstrated that the charging resistance for both the PPy-DBS/CNT and PPy-Cl/CNT electrodes was dramatically reduced and only about 10% that of the CNT electrode. By pairing the two composite electrodes with CNT electrodes, four cells were assembled to study the effects of electrode assembling patterns on the desalination performance of the CDI process. The results indicated that the CDI cells involving either the PPy-DBS/CNT electrode or the PPy-Cl/CNT electrode, or both of them exhibited much higher electrosorption capacity (from 40.8 to 72.36 mg/g) than that of the CDI cell assembled with two CNT electrodes (about 12.6 mg/g). And the composite electrodes kept good stability and fast regeneration rate after several desalting cycles. Thus, it is believed that the enhanced performance and optimized electrode assembly of the CDI cell should be with the composite electrodes that have the good ability of ion selective adsorption for cations or anions.