Hierarchical Co₃O₄/CNT decorated electrospun hollow nanofiber for efficient hybrid capacitive deionization

Hybrid capacitive deionization (HCDI) is emerging as an energy-efficient alternative for brackish water desalination with low expenditure cost and favourable ion removal effectiveness by adopting battery-type electrodes in the traditional capacitive deionization (CDI) system. Herein, an unscalable electrospinning method is introduced to contrive cathode material for HCDI system. Co₃O₄ and nitrogen-doped carbon nanotube decoration are formed successfully and uniformly distributed with the hollow structure of free-standing carbon nanofibers (Co₃O₄@CNF@CNT). The conductive “bridges” provided by the CNF matrix significantly shorten the diffusion length of Na+ and promote the electrical conductivity of the Co₃O₄ nanoparticles. Moreover, benefiting from the incorporation of nitrogen-doped CNTs, the electrical conductivity is further enhanced. The as-prepared Co₃O₄@CNF@CNT cathode shows excellent pseudocapacitive performance of 395F g⁻¹ at a scan rate of 1 mV s⁻¹ and superior rate performance of 279F g⁻¹ at 100 mV s⁻¹. The HCDI system delivers an outstanding salt adsorption capacity (SAC) of 58.6 mg g⁻¹ and a highest salt adsorption rate (SAR) of 12.27 mg g⁻¹ min⁻¹ with a potential difference of 1.4 V, indicating the great potential of applying Co₃O₄@CNF@CNT in the practical HCDI system.