Carbon nanotube wrapped hydrogen-bonded organic frameworks towards superior Na+ storage in the capacitive deionization process

Abstract

Hydrogen-bonded organic frameworks (HOFs) become promising candidates in the capacitive deionization (CDI) technology due to their prominent redox reaction. Herein, the novel CNTs@HOF-DAT composite with the three-dimensional interwoven-network structure is prepared by the facile solvothermal synthesis and applied to the CDI technology for the first time. The synergistic effect between the special structure of HOF-DAT (multiple hydrogen bonds, abundant heteroatoms and π-π interactions) and the high conductivity of CNTs stimulates more redox active sites for the ion storage and accumulation in the CNTs@HOF-DAT composite. This makes the CNTs@HOF-DAT electrode have a high specific capacitance (152.5 F∙g−1) and an improved pseudo-capacitance contribution (49 %). Also, the ion removal capacity (16.33 mg∙g−1) of the CNTs@HOF-DAT electrode greatly surpasses that of the single HOF-DAT electrode (3.23 mg∙g−1) and CNTs electrode (8.77 mg∙g−1). Significantly, the desalination mechanism of the CNTs@HOF-DAT composite electrode is explored in terms of the electrode configurating mode and zero-charge potential of the three prepared electrodes, as well as the redox reaction of the HOF-DAT molecules, which manifests that the CNTs@HOF-DAT electrode is suitable as the cathode of the CDI cell.