Optimizing Membrane Capacitive Deionization Performance through Tailored Pore Size Distribution

Abstract

Membrane capacitive deionization (MCDI) has emerged as an efficient technology for brackish water desalination, operating by immobilizing ions within porous carbon electrodes under an electrical field. Porous carbon materials are considered a highly promising candidate for MCDI due to their tunable pore structures and high surface area. However, the precise relationship between their pore size distribution and MCDI performance remains unclear. Herein, we have prepared porous electrodes with varied pore size distributions via a molten salt-assisted exfoliation-evaporation strategy. This study provides direct experimental evidence that the pore size distribution is a critical determinant of MCDI efficiency, with narrow mesopores centered around 2 nm in size contributing most significantly to ion adsorption. This optimal size is attributed to efficient double-layer formation in confined spaces. By strategically tailoring the electrode’s porosity toward this favorable distribution, a remarkable salt adsorption capacity of 52.36 mg g-1 and an average desalination rate of 1.75 mg g-1 min-1 have been achieved. Optimization of the hierarchical pore structure of carbon electrodes presents a promising pathway for pushing MCDI performance closer to its thermodynamic limits.