Urchin-like core–shell tungsten oxide@carbon composite electrode for highly efficient and stable water desalination via hybrid capacitive deionization (HCDI)

W18O49 has been considered as a promising candidate for electrochemical applications, but it suffers from unsatisfactory electrical conductivity, low specific surface area, poor structural stability, and the corresponding morphology dependent capacitive deionization (CDI) performance has not been reported. Herein, we explored the novel composites of various morphologies of W18O49 encapsulated by a carbon shell (W18O49@C) as hybrid capacitive deionization (HCDI) cathode for water desalination. The as-obtained W18O49@C exhibited unique structures, allowing synergistic effects of ion intercalation and electric-double-layer capacitance, fast ion penetration, rapid electron transfer, and dissolution prevention of the active core materials. Among the three morphologies of W18O49@C, urchin-like W18O49@C (UWC) presented appropriate pore size distribution, the largest specific surface area and specific capacitance, the highest degree of graphitization and carbon content, consequently achieving excellent desalination capacity. Furthermore, an outstanding cycling stability over 200 cycles as well as a high charge efficiency and a low energy consumption were displayed for the UWC electrode. This study illustrates the great promise of urchin-like core–shell tungsten oxide@carbon composite in HCDI and paves a way for rational design of highly efficient and stable electrode materials for water desalination.