Three‐dimensional graphene/MWCNT-MnO2 nanocomposites for high‐performance capacitive deionization (CDI) application

[Display omitted] •3D nanocomposite materials prepared by embedding MWCNT-MnO2 between interconnected graphene layers.•Excellent salt adsorption capacity of 65.1 mg (NaCl) g-1 has been observed under 1.2 V and 600 ppm NaCl solution.•The structure and morphology of the 3D composites materials have been thoroughly studied.•The structure and morphology of the 3D composites materials have been correlated with the electrochemical performance. Surface area and the conductivity of the electrode materials are crucial in achieving high desalination performance in capacitive deionization (CDI) applications. In this study, we have successfully fabricated 3D Graphene/MWCNT-MnO2 nanocomposites by self-assembling negatively charged manganese dioxide (MnO2) decorated with multiwall carbon nanotube (MWCNT) and positive graphene oxide (GO). The MWCNT-MnO2 was prepared by the uniform decoration of MnO2 nanoparticles on the MWCNT surface, and positive GO was prepared by functionalizing the GO surface with ethylenediamine. The 3D composite was obtained by self-assembling positive GO and negative MWCNT-MnO2 via electrostatic co-precipitation method followed by hydrothermal treatment. The structure and morphology of the 3D composites materials are thoroughly studied and correlated with the electrochemical performance. Cyclic voltammetry (CV) curves exhibit high specific capacitances and depict a quasi-rectangular shape, suggesting a high pseudo-capacitive behavior resulting from electrical double-layer (EDL) at the electrode-solution interface and the presence of MnO2. The salt electrosorption capacity of the 3D composites investigated using 600 ppm NaCl solution and 1.2 V showed the highest salt adsorption capacity of 65.1mgNaClg-1. The excellent performance of the 3D composite materials as the electrode is attributed to the three-dimensional macroporous architectures and a high pseudo-capacitive behavior. Moreover, the study suggests that the electrode performance can be altered by choosing suitable anode materials.