Hierarchical tubular Co3O4/CNT structures for Efficient Hybrid Capacitive Deionization

Abstract

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 as the “medium”, the contact between electrolyte and electrode material is improved and the electrical conductivity is further enhanced. The as-prepared Co3O4@CNF@CNT cathode shows excellent pseudocapacitive performance of 395 F g-1 at a scan rate of 1 mV s-1 and superior rate performance of 279 F 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.