High performance ordered mesoporous carbon/carbon nanotube composite electrodes for capacitive deionization

Abstract

In this study, a novel ordered mesoporous carbon/carbon nanotube (OMC/CNT) composite electrode was proposed and its capacitive deionization properties were investigated in aqueous solution. The OMC/CNT composites were obtained by an organic–inorganic self-assembly route. SEM and TEM observations show the 2D hexagonally ordered mesoporous channels and nanotubular morphology of the composites. The OMC/CNT composites with high specific surface area and excellent conductivity are favorable for capacitance deionization due to the easily available electrochemical double layer behaviors. The electrochemical properties are measured by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements. Through all the measurements above, it was found that the OMC/CNT electrodes with 10 wt% of CNTs exhibit superiority in electrosorption capacitance, low resistance, high reversibility and electrochemical stability during the charge/discharge process. The comparative electrosorption properties of the OMC/CNT electrodes were also investigated in various aqueous solutions, and it is found that the electrosorption capability of the OMC/CNT electrodes depends on the hydration radius and valence of the ions in the aqueous solutions. The power and energy density were evaluated by a pair of OMC/CNT electrodes with various current loads, and this showed that the OMC/CNT composite electrodes have higher power density and lower energy density characteristics as compared with the pristine OMC electrode, which indicates that the composite electrodes exhibit low energy consumption for capacitive deionization. In desalination measurements, the OMC/CNT composite electrodes exhibit excellent desalination behavior in a flow-through apparatus, which is attributed to the low resistance and high specific surface area.