Design, Synthesis, Crystal Structure, and Thermal Studies of Ni0.779SbF3(SO4): A New Electrode Material for Electrochemical Supercapacitors

A new transition-metal-based antimony fluoride sulfate compound, Ni0.779SbF3(SO4), has been studied, which appears to be a promising candidate for an electrode material in supercapacitor devices. The hydrothermal synthetic technique has been employed for growing single crystals. The single-crystal X-ray diffraction study reveals that it crystallizes in the orthorhombic space group Cmce with unit cell parameters a = 15.1710 (3) Å, b = 7.1843 (11) Å, and c = 11.070 (17) Å and Z = 8. The crystal structure consists of a [SbF3O2] polyhedron and a [SO4] tetrahedron along with cis- and trans- [NiO4F2] octahedrons of two different Ni atoms that result in negatively charged [NiSbF3·SO4] n layers in the crystal structure, where each layer is made up of chains of [Ni(1)­O6F2] n , [Ni(2)­O8F2] n , and [(SbF3)2(SO4)2] n 4–. The partial occupancy on Ni sites resulted in the compound being nonstoichiometric. The morphological analysis by both scanning electron microscopy (SEM) and tunneling electron microscopy (TEM) reveals a multilayer dense nanoflake-like morphology. Thermogravimetric analysis (TG-DTA) shows that the compound has a high thermal stability with a decomposition temperature above 450 °C. The density functional theory (DFT) and density of states (DOS) are found to be commensurate with the experimental results. The material shows good electrochemical performance with a capacitance of 245 F g–1 at a specific current density of 1 A g–1. Further, the electrochemical impedance spectroscopy (EIS) study confirms the capacitive nature of the electrode.