Surfactant assisted-SnO₂ nanorods and nanoflowers synthesised by hydrothermal method for supercapacitor applications

In this article, using polyvinyl alcohol (PVA) and sodium hexametaphosphate (SHP) as a surfactant solution, tetragonal SnO₂ nanoparticles (NPs) were synthesised using the hydrothermal technique. NPs resulting from this process are named Sn-SHP and Sn-PVA.X-ray diffraction study revealed tetragonal crystal structure for both Sn-SHP and Sn-PVA nanoparticles, matching well with the JCPDS Card No. 88-0287. Scanning electron microscopy (SEM) showed rod-shaped Sn-SHP NPs, whereas Sn-PVA NPs have flower-like forms. A band gap energy of 3.71 and 3.84 eV was measured for the Sn-SHP and the Sn-PVA nanoparticles. The various oxidation states of SnO₂ were confirmed by XPS spectra in order to confirm its oxidation states. The electrodes were analysed by using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical ion spectroscopy (EIS) in 6 M KOH electrolytes. For Sn-PVA electrodes, the computed specific capacitance (C_s) values are 330.52, 71.25, 27.34, and 18.85 Fg⁻¹ at scan rates of 2, 10, 30, and 50 mVs⁻¹; whereas for Sn-SHP electrodes, the obtained values are 256.24, 55.46, 21.04, and 14.45 Fg⁻¹ at scan rates of 2, 10, 30, and 50 mVs⁻¹. Additionally, from the GCD curves demonstrate that the Sn-PVA electrode has C_s of 126, 98, 81, and 71 Fg⁻¹, and Sn-SHP electrodes revealed C_s of 75.65, 66.44, 48.69, and 25.97 Fg⁻¹ at current density of 1, 2, 4, and 6 Ag⁻¹, respectively. Galvanostatic charge–discharge curves for Sn-SHP and Sn-PVA NPs were traced in a potential window ranging from 0.03 to 0.4 V, and it was ascertained that Sn-PVA with flower shaped nanoparticles retains S_c of 126 Fg⁻¹ at current density of 1 Ag⁻¹, making it potential candidate for supercapacitor applications.