Rational design and fabrication of graphene/carbon nanotubes hybrid sponge for high-performance capacitive deionization

Capacitive deionization (CDI) is an emerging technology offering a green and efficient route to obtain clean water. Up to now, the key of CDI technology has been focused on the exploration of electrode materials with a rationally designed structure and excellent performance, because the electrosorption performance of the carbon-based electrodes reported to date cannot meet the demands of practical applications of CDI. Herein, novel graphene/carbon nanotubes (CNTs) hybrid sponge (GNS) structures were designed and fabricated via directly freeze-drying graphene oxide/CNTs mixed solution followed by annealing in nitrogen atmosphere. The morphology, structure and electrochemical performance of GNS were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that GNS with 20 wt% CNTs has a maximum specific surface area of 498.2 m² g^-1 and a highest specific capacitance of 203.48 F g^-1 among all the samples. When used as CDI electrode, it exhibits an ultrahigh electrosorption capacity of 18.7 mg g^-1, and, to our knowledge, this value is superior to those of other carbon electrodes reported recently. GNS should be a promising electrode material for high-performance CDI.