Facile synthesis of BiSI and Bi13S18I2 as stable electrode materials for supercapacitor applications

Abstract

In this paper, we demonstrate a novel synthetic route of two bismuth chalcogenide materials 3-D hexagonal Bi₁₃S₁₈I₂ and 3-D orthorhombic BiSI, and investigate their potential as the active electrode material for supercapacitors. Both pure BiSI and Bi₁₃S₁₈I₂ powders were obtained for the first time at relatively low temperature (120 °C) in a solution system. We studied the effects of different reaction conditions on the surface morphology of the product and found that at a relatively low temperature of 120 °C under atmospheric pressure, the materials can yield smaller crystallite size and higher specific surface area, further increasing the capacitance compared to the synthesis under hydrothermal conditions. Cyclic voltammetry and galvanostatic charge–discharge measurements of the materials were studied using three-electrode and two-electrode configurations at a variety of currents. The galvanostatic charge–discharge measurement results show that the Bi₁₃S₁₈I₂ electrode has a maximum areal capacitance of 247 mF cm⁻² at the current density of 5 mA cm⁻² and excellent capacitance retention of 98.4% after 5000 cycles at the current density of 50 mA cm⁻² in 3.0 M KOH electrolyte as a two-electrode electrical double-layer capacitor system (EDLC). The BiSI and Bi₁₃S₁₈I₂ powders have been characterized through PXRD, XPS, Raman spectroscopy, TGA–DSC, BET, SEM and TEM. This facile route to the synthesis of both Bi₁₃S₁₈I₂ and BiSI with superior stability has promising potential for low-cost and effective electrochemical supercapacitor applications.