Ag-doped sepiolite intercalated graphene nanostructure for hybrid capacitive deionization system

Hybrid capacitive deionization (HCDI) is one of the effective desalination technologies that consists of faradic and non-faradic carbon electrodes. Herein, an ion-exchange membrane-free HCDI system has been developed using sepiolite intercalated graphene (GS) and silver (Ag)-doped sepiolite intercalated graphene (AGS) as the cathode and anode, respectively. Electrochemical studies were revealed that the GS hybrid electrode provides an electrical double layer (EDL) with a specific capacitance of 73 F g⁻¹, whereas the AGS exhibited pseudocapacitive behavior with a specific capacitance of 97.5 F g⁻¹ at 10 mV s⁻¹ in 2 M NaCl solution. AGS electrode was selectively intercalating the anions from the salt solution and prevented the co-ion repulsion, resulting in a significant salt adsorption capacity of 20.7 mg g⁻¹ and charge efficiency of 87.1% at 1.2 V in 600 mg L⁻¹ of NaCl solution. The presence of nanoclay in the hybrid exhibits intrinsic hydrophilicity and more stability of the electrode, resulting in a stable cycling performance over the 10 charge-discharge cycles. Moreover, by utilizing the advantage of the hybrid materials, ions are selectively captured in the HCDI cell via both the electrochemical faradic reaction and electrostatic EDL mechanism. Thus, the GS and the AGS hybrid materials exhibited good desalination performance in the HCDI application.