Chinese dumpling-like NaTi₂(PO₄)₃/MXene@reduced graphene oxide for capacitive deionization with high capacity and good cycling stability

Capacitive deionization (CDI) has emerged as a potential energy-efficient desalination technique to provide fresh water from brine, and the rational design of deionization electrodes remains a challenge. Cation insertion materials hold great potential in desalination and selective ion separation due to suitable space to intercalate cations; however, intrinsically low electrical conductivity and poor stability impede their further application in CDI. In this research, a partial in situ derivation tactic was proposed to address these problems by using Ti-based MXenes as metal precursors. The as-prepared NTP-MXene/rGO hybrid resembles the morphology of dumplings, where MXene/rGO serves as the skin to protect the NTP filling and enhance its electrical conductivity. This composite electrode material exhibited an outstanding salt adsorption capacity (SAC) of 251.55 mg g⁻¹ in constant current mode with a specific current of 50 mA g⁻¹ (cutoff voltage: 1.8 V; initial NaCl concentration: 10 mM), far higher than those of reported materials. Moreover, low energy consumption (0.19 kW h kg_NaCl⁻¹) was obtained at a cutoff voltage of 1 V, and stable cycling performance (approximately 80% capacity was retained after 100 cycles) makes M-NTP/rGO a suitable electrode for practical applications, proving that partial derivation is an attractive strategy in rational design of CDI electrodes. © 2023 The Royal Society of Chemistry.