Preparation of Layered Structure MnO2/CNTs Composites for High-Performance Salt Removal by Hybrid Capacitive Deionization

Capacity deionization (CDI), which combines capacitive carbon electrodes and redox-active electrodes, has emerged as a promising method for water desalination. It enables higher ion removal capacity than CDI-containing carbonaceous electrodes. Our work aimed to synthesize layered structure δ-MnO2/CNTs composites via the sol-gel method, examining their suitability for hybrid capacitive deionization (HCDI). The XRD results showed a layered structure birnessite for all composites with a distance interlayer over 7.0 Å, while the SEM images confirmed the intercopration of MnO2 particles and CNT fibers. The electrochemical evaluations evidenced the role of CNTs in enhancing the charge transfer and ionic diffusion in composites. Composite δ-MnO2/CNTs presented a specific capacitance of 160 F g−1 at a charge-discharge rate of 1 A g-1 upon 1600 cycles. In salt removal performance, the asymmetric cell AC||δ-MnO2/CNTs-1 showed the highest salt adsorption capacity (SAC) of 30.2 mg g−1 and fast average salt adsorption rate (ASAR) of 3 mg g−1 s−1 under a constant applied potential 1.4 V in 200 ppm NaCl, rendering it a promising candidate for efficient and sustainable desalination technology.