Co-Co3O4 encapsulated in nitrogen-doped carbon nanotubes for capacitive desalination: Effects of nano-confinement and cobalt speciation

Capacitive deionization (CDI) has gained increasing attention as an environmentally friendly and energyefficient technology for brackish water desalination. However, traditional CDI electrodes still suffer from low salt adsorption capacity and unsatisfactory reusability, which inhibit its application for long-term operations. Herein, we present a facile and effective approach to prepare Co and Co3O4 nanoparticles co-incorporating nitrogen-doped (N-doped) carbon nanotubes (Co-Co3O4/N-CNTs) via a pyrolysis route. The Co- Co3O4 nanoparticles were homogeneously in-situ encapsulated in the inner channels of the conductive CNTs to form a novel and efficient CDI electrode for the first time. The encapsulation of Co-Co3O4 nanoparticles in CNTs not only inhibits the Co leaching but also significantly enhances the desalination capacity. The morphology, structure, and capacitive desalination properties of the Co-Co3O4/N-CNTs were thoroughly characterized to illuminate the nano-confinement effects and the key roles of the interaction between cobalt species in the CDI performance. The co-existing metallic cobalt and cobalt oxides act as the roles of effective active sites in the CDI performance. As a consequence, the optimum Co-Co3O4/NCNTs electrode displays an outstanding desalination capacity of 66.91 mg NaCl g(-1) at 1.4 V. This work provides insights for understanding the nano-confinement effects and the key roles of the interaction between cobalt species on the CDI performance. (C) 2022 Elsevier Inc. All rights reserved.

Automated summary

This study presents a facile and effective approach to prepare Co and Co3O4 nanoparticles co-incorporating nitrogen-doped carbon nanotubes (Co-Co3O4/N-CNTs) as a novel and efficient CDI electrode. The encapsulation of Co-Co3O4 nanoparticles in CNTs inhibits Co leaching and enhances the desalination capacity. The optimized Co-Co3O4/N-CNTs electrode exhibits outstanding desalination capacity of 66.91 mg NaCl g(-1) at 1.4 V.