Hierarchical composite of N-doped carbon sphere and holey graphene hydrogel for high-performance capacitive deionization

Capacitive deionization (CDI) is a promising technique for water treatment and desalination. To enable high CDI performance, the electrode materials should possess high surface area, conductivity, hydrophilicity, and cycling stability. Here, we report the design and construction of a hierarchical porous composite of N-doped hollow mesoporous carbon sphere and holey graphene hydrogel with in-plane pores, i.e., N-HMCS/HGH composite, for high-performance CDI. The N-HMCS/HGH composite shows a three-dimensional (3D), hierarchical porous structure with a specific surface area of 337.7 m(2) g(-1), high conductivity, and high hydrophilicity. With these structural characteristics, the optimized N-HMCS/HGH electrode exhibits a large specific capacitance (226.5 F g(-1)) in 0.5 M NaCl solution to ensure a large electrosorption capacity of 17.8 and 32 mg g(-1) in a feeding NaCl solution with initial concentration of 500 and 2500 mg L-1, respectively. Upon 35 CDI-regeneration cycles, the electrosorption capacity of the N-HMCS/HGH electrode shows no obvious attenuation, exhibiting excellent cycling stability. These results indicate that the hierarchical N-HMCS/HGH composite shows great potential for practical application.