One-pot preparation and the electrochemical properties of the composite of the NiCo bimetallic organic framework and carbon quantum dots

Abstract

Designing metal–organic framework (MOF) materials with high conductivity is crucial for their application in energy storage devices. In this study, a simple process, namely, a one-pot hydrothermal method, was used for simultaneously synthesizing the composite of carbon quantum dots (CQDs) and NiCo-MOF, and the effect of various carbon sources for CQDs was compared. The results showed that it was very necessary to choose an appropriate carbon source for obtaining NiCo-MOF with the expected lower R_s and R_ct. Carbon sources significantly affected the morphology of NiCo-MOF, and in turn its specific surface area, pore volume and pore size. Particularly, after introducing CQDs derived from citric acid, the electron cloud density around the metal Co atom in the NiCo-MOF composite became higher, improving electron transfer ability, activating the metal center Co and alleviating polarization. As a result, the obtained NiCo-MOF-CA composite exhibited a capacitance of 1826.8 F g⁻¹ at 1 A g⁻¹, significantly higher than that of NiCo-MOF (1060.3 F g⁻¹). An amplifying circuit model was proposed for explaining the phenomenon. Its cyclic performance also became better, but still left to be further improved. The simple synthesis process might be applied to the preparation of other similar composites. In addition, the conductivity of MOFs was improved by introducing specific conductive additives to alter the electronic structure of the metal atom in active materials, providing an effective strategy for other researchers.