Pore optimization engineering for enhancing ion storage and capacitive deionization properties of graphene

Abstract

Graphene is widely acknowledged as an exceptional electrode material for Capacitive Deionization (CDI) technology, owing to its unique crystal structure and electron transport properties. Typically, three-dimensional graphene is formed by stacking graphene nanosheets in a card-like manner. However, the assembly of these nanosheet layers results in numerous closed and narrow slit-like pores, which diminish pore connectivity and consequently limit its ion storage and capacitive deionization performance. Here, we employed KOH-assisted low-temperature rapid etching of three-dimensional reduced graphene oxide to construct a three-dimensional porous graphene (3D-PG) structure, thereby optimizing the distribution of pores. The 3D-PG electrode retained the open, interconnected three-dimensional structure and excellent conductivity of graphene. The unobstructed pores facilitated deeper ion diffusion and increased ion storage sites, significantly enhancing the ion storage capacity. Therefore, the 3D-PG electrodes exhibit exceptional electrochemical and CDI performance, with a specific capacitance of up to 348F/g at 1 A/g, retaining 99.7 % of this capacitance after 5000 cycles. Additionally, at an initial NaCl concentration of 1000 mg/L and a voltage of 1.6 V, the salt adsorption capacity (SAC) reached 24.5 mg/g, significantly outperforming many other graphene materials. These findings pave the way for synthesizing high-performance graphene-based materials on a large scale, with extensive potential for application in CDI and beyond.