Capacitive deionization of NaCl solutions using carbon nanotube sponge electrodes

Abstract

Capacitive Deionization (CDI) is a promising method for desalination of brackish water because of its energy-efficiency as compared with conventional techniques such as membrane separation and thermal distillation. Carbon nanotube (CNT) sponges, prepared by chemical vapor deposition, are very flexible and have three-dimensional continuous and mesoporous structures, making them promising electrode materials for capacitive deionization. The CDI characteristics of CNT sponges were investigated for the first time by simply compressing them into a CDI cell without any additives. Desalination of NaCl solutions at different concentrations was conducted with a flow-through CDI cell at 1.2V. Experimental data fit well with the Langmuir model, and the deduced maximum desalination capacity was 40 mg g⁻¹, almost 50% higher than the optimal result reported in the literature. By comparing with other carbon-based materials, the excellent CDI performance of CNT sponges was attributed to higher conductivity and larger effective surface area due to their monolithic continuous flexible framework, crystalline microstructure and preferred pore size distribution.