Holey graphene hydrogel with in-plane pores for high-performance capacitive desalination

Capacitive deionization is an attractive approach to water desalination and treatment. To achieve efficient capacitative desalination, rationally designed electrodes with high specific capacitances, conductivities, and stabilities are necessary. Here we report the construction of a three-dimensional (3D) holey graphene hydrogel (HGH). This material contains abundant in-plane pores, offering efficient ion transport pathways. Furthermore, it forms a highly interconnected network of graphene sheets, providing efficient electron transport pathways, and its 3D hierarchical porous structure can provide a large specific surface area for the adsorption and storage of ions. Consequently, HGH serves as a binder-free electrode material with excellent electrical conductivity. Cyclic voltammetry (CV) measurements indicate that the optimized HGH can achieve specific capacitances of 358.4 F·g^-1 in 6 M KOH solution and 148 F·g^-1 in 0.5 M NaCl solution. Because of these high capacitances, HGH has a desalination capacity as high as 26.8 mg·g^-1 (applied potential: 1.2 V; initial NaCl concentration: ~5, 000 mg·L^-1).