Hybrid pseudocapacitive sodium titanate/rGO and MXene/rGO nanocomposite electrodes in capacitive deionization

Abstract

Two hybrid pseudocapacitive materials Na8Ti5O14/rGO (NTO/rGO) and Ti3C2Tx/rGO (MXene/rGO) were successfully synthesized using two-step easy hydrothermal processes, respectively. In this carefully nano-engineered architecture, the dense structure of NTO synthesized firstly were intertwined with the rGO nanosheets framework; whereas the highly organized thoroughly exfoliated MXene nanosheet were deposited with rGO nanosheets. The electrochemical capacitances of both hybrid pseudocapacitive nanocomposites were increased by 99.7 % and 72.7 % compared to the nanocrystals only, the capacitance retention and impendence were also improved. In the CDI experiments, the high salt removal capacities of the hybrid nanocomposite NTO/rGO and MXene/rGO were obtained as 75.6 mg g−1 and 64.3 mg g−1, which exceeded other reported values using similar electrodes. A 100 % regeneration in multiple cycles was achieved. This high desalting performance was attributed to the synergistic effect of efficient ion intercalation along with enhanced electrical conductivity and structure accessibility. These hybrid mechanism of ion intercalation and electrical double layer formation in action opened up the possibility of using hybrid pseudocapacitive nanocomposite electrodes such as Na8Ti5O14/rGO and Ti3C2Tx/rGO for effective capacitive desalination. Their respective selectivity in aqueous ionic solution will be investigated in future studies.