Effects of Impurities on the Electrochemical Characterization of Liquid-Phase Exfoliated Niobium Diselenide Nanosheets

Commercially available bulk niobium diselenide (NbSe 2 ) reduced into nanomaterials upon exfoliation typically contains oxide and carbide impurities. Liquid-phase exfoliated two-dimensional (2D) nanosheets of NbSe 2 obtained from bulk powders provide high charge mobility and large surface area but become self-passivated and chemically inert as the presence of oxide impurities makes them behave more semimetallic. In this article, we report the effects of inherent impurities of liquid-phase exfoliated 2D NbSe 2 (intended to be integrated as supercapacitor electrodes) on the electrochemical performance. The highest specific capacitances achieved using 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF 6 ) and sulfuric acid (1 M H 2 SO 4 ) electrolytes were 4955.5 ± 21.5 and 13 361.6 ± 31.8% mF/cm 2, respectively, which were affected by the impurities, oxophilicity of niobium defects, and moisture adsorption in the cell. Galvanostatic charge–discharge profiles show moisture adsorption affecting the high-energy charging procedure in the cell for BMIMPF 6, resulting in leakage and decomposition of the electrolyte. Electrochemical impedance spectroscopy provides insights into the solid-electrolyte interphase and charge-transfer mechanisms at exfoliated 2D NbSe 2 nanosheets, which affect the ion intercalation through heterogenous phases of the nanosheets. Overall, the NbSe 2 nanosheets offer heterogenous phases because of the coexistence of Nb 2 O 5 that influences the charge-transfer mechanism at the exfoliated surfaces.