Controlled synthesis of NaTi₂(PO₄)₃/Carbon composite derived from Metal-organic-frameworks as highly-efficient electrodes for hybrid capacitive deionization

Hybrid capacitive deionization (HCDI), as a major branch of capacitive deionization (CDI), was acknowledged as one of the most promising electrochemical desalination techniques due to its ultrahigh desalination capacity and charge efficiency. Among various HCDI electrode materials, polyanion compounds (NaTi₂(PO₄)₃ (NTP) for instance) have attracted great attention owing to their stable 3D crystal structure and high theoretical capacity. Yet, an important correlation between the surface morphology and desalination performance of the NTP-based composite is still missing, which has become a limitation for the further development of NTP-based HCDI. Herein, we prepared a series of NaTi₂(PO₄)₃/Carbon (NTP/C) composites from metal-organic frameworks with different surface morphologies and subsequently used them as the cathode for HCDI. After systematical study, we found that the surface morphology of the NTP/C has a significant impact on its desalination performance, while the cube/sphere-shaped NTP/C exhibits the highest desalination capacity (74.6 mg g⁻¹) with outstanding long-term stability (only 10 % capacity fading after 35 cycles). The vastly different desalination performance indicates that the surface morphology could greatly affect the “packing density” and charge transfer resistance of the NTP/C, and subsequently influence its desalination performance.