MnO2-Coated Graphene/Polypyrrole Hybrids for Enhanced Capacitive Deionization Performance of Cu2+ Removal

Capacitive deionization (CDI) technology, a promising desalination technology, can be applied to the enrichment and recovery of valuable resources as well as wastewater treatment and purification. However, electrode performances such as electrochemical conductivity and electrosorption capacity both play an important role in CDI application. In this study, we deposited MnO2 and PPy on the surface of graphene oxide by lay-lay electrodeposition to obtain an ideal composite electrode (denoted as GO/PPy/MnO2) for CDI. The electrochemical characterizations indicated that the GO/PPy/MnO2 electrode had a high specific capacitance of 356.58F/g and better cycling stability. The presence of PPy and MnO2 leads to a significant improvement in the electrochemical properties of the electrode, which contained rapid Faradaic charge-transfer reactions and pseudocapacitive charge storage. Furthermore, a series of electrosorption experiments were carried out at 1.2 V in 1 mM CuSO4 aqueous solution. As evidenced, the GO/PPy/MnO2 composite has an excellent Cu2+ ion adsorption capacity of 38.4 mg/g, which is significantly higher than that of GO/PPy electrodes. Hence, when the GO/PPy/MnO2 composite is used as a cathode, an enhanced CDI performance is achieved through a combination of static electricity as well as Faradaic processes, owing to the two removal mechanisms of capacitive electro-sorption and pseudocapacitive redox reactions. This study provided an efficient strategy for using MnO2 and PPy on GO substrates to improve electrosorption performance.