In situ generation of reduced graphene oxide on 3D CuNi foam as high-performance electrodes for capacitive deionization

Capacitive deionization (CDI) is one of the high-efficient technologies for desalination of brackish water. In this paper, a composite electrode with 3D CuNi foam (CNF) as current collector and reduced graphene oxide (rGO) as active material was synthesized, in which graphene oxide was reduced in situ and immobilized on the 3D CNF. Obtained rGO/CNF electrodes were directly employed as anode and cathode in a CDI cell. The effects of different substitution reaction time on the electrodes were investigated by SEM, XRD, Raman and XPS. Results showed that the existence of Cu on CNF could adjust the morphology and the defect content of rGO. The specific capacity of rGO/CNF-1.5 electrode (Note: 1.5 stands for the substitution reaction time) reached 352.5 F·g−1 at 5 mV·s−1 in 1.0 M NaCl electrolyte. During desalination, the rGO/CNF-1.5 electrode has a high salt adsorption capacity (SAC) of 84.6 mg/g in 250 mg/L NaCl solution at 1.2 V, which is 2.23 times higher than that of rGO/NF. The high performance of desalination can be attributed to the formation of electric double layer capacitance and pseudocapacitance. After 20 cycles, the SAC of rGO/CNF-1.5 electrode remains at 77.1 mg/g which is over 91 % of the original SAC.