Graphene Oxide-Tuned MoS2 with an Expanded Interlayer for Efficient Hybrid Capacitive Deionization

Capacitive deionization (CDI) has shown great promise in desalinating salt water; however, conventional CDI electrode materials suffer from low specific salt capacity and charge efficiency owing to the co-ion expulsion effect. Herein, using expanded MoS2 nanosheets supported by reduced graphene oxide (MoS2/rGO) as the intercalation electrode, we develop a hybrid CDI system that shows a battery-like behavior and can reversibly store cations through the intercalation mechanism. The incorporation of rGO in the composite not only affords a conductive support and ensures fast electron transfer but also, more importantly, widens the MoS2 interlayer spacing from 0.62 to 0.73 nm. The expanded MoS2 interlayer facilitates the diffusion of cations and decreases the internal strain during the intercalation/de-intercalation process. Also, it endows MoS2/rGO with more accessible sites and space for cations in the electrolyte. Benefiting from the desirable structure features, the hybrid CDI system delivers a remarkable specific salt capacity of 34.20 mg g–1 and a charge efficiency as high as 97% in 300 mg L–1 sodium chloride aqueous solution. The MoS2/rGO involved in the CDI system for the adsorption of other metal ions is also verified, indicating its potential applications for the removal of various metal ions in brackish water and seawater.