3D graphene-supported N-doped hierarchically porous carbon for capacitive deionization of saline water

Abstract

Capacitive deionization (CDI) is a promising technique for desalination of brackish water because it is highly energy-efficient and environmentally friendly. However, one of the most challenging issues in developing CDI technologies is the rational design and synthesis of active electrode materials, with favorable morphologies, reasonable porous structure, excellent electrical conductivity and hydrophilicity. Herein, three-dimensional graphene-supported N-doped hierarchically porous carbon (3DNHPC) is rationally designed and originally prepared and applied in electrode materials for capacitive deionization. The 3DNHPCs are fabricated by a simple template-direct method using polyacrylonitrile coated polystyrene spheres as templates. The synthetic composites based on graphene have a hierarchically porous nanostructure with hollow mesoporous carbon spheres uniformly embedded in the graphene sheets. The hierarchically porous structure of 3DNHPC electrodes can ensure fast transport of salt ions and N-doped carbon can provide a bulk of adsorption sites for the formation of an electrical double layer due to its high specific surface area. Furthermore, the graphene sheets in 3DNHPC act as the interconnected conductive networks resulting in fast charge transfer. Benefiting from the unique 3DNHPC structure, the composites possess high specific capacitance, low inner resistance and long cycling lifetime. A stable capacitive deionization performance with 25.5 mg g⁻¹ salt adsorption capacity was achieved. The results presented in this work open a new window for the development of highly energy efficient desalination of saline water.