WSe₂ Nanoflakes on Graphite Sheets for Flexible Symmetric Supercapacitors

Abstract

In this study, we have investigated the electrochemical performances of a flexible symmetric supercapacitor (FSS) device based on WSe 2 nanoflakes thin film electrodes. The nanoflakes thin film electrodes were fabricated using environmentally friendly and costeffective DC magnetron sputtering. The as-prepared FSS device was tested in four different aqueous electrolytes containing group 1 alkali metal cations (HCl, LiCl, NaCl, and KCl), using several techniques, including cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy. The obtained results revealed that the FSS devices based on WSe 2 with nanoflake-type morphology in various electrolytes exhibit distinctive double-layer characteristics. The device tested in HCl electrolyte demonstrated the highest electrochemical performance, including an impressive areal capacitance of 88 mF cm −2 with corresponding energy and power density of 27.5 μWh cm −2 and 3000 μW cm −2 , respectively, at a constant current density of 4 mA cm −2 , along with a solution resistance of 0.5 Ω, within an operating voltage range of 1.5 V. The cationic mobility (Li + < Na + < K + < H + ) affects ionic conductivity, efficient ion/charge transition, as well as relaxation time and is found to be directly correlated with capacitance value. On the other hand, the order of the long-term cycle stability (LiCl < NaCl < HCl < KCl) is caused by the intricate interactions between ion size, charge density, mechanical stresses, and chemical interactions with the electrode material during the charging and discharging cycles. Furthermore, the use of 1 M HCl as an electrolyte yields superior capacitance performance (88 mF cm −2 ) and high cycling stability (75.36% capacitance retention after 5000 cycles) at 4 mA cm −2 . As a result, the electrolyte cations exert a significant impact on the electrochemical performance of the FSS.