Electrochemical analysis of flexible symmetric supercapacitors using WSe ₂ @graphite thin film electrodes under different pH conditions

A key focus of this research is to investigate the influence of electrolyte pH on the supercapacitive performance of a flexible symmetric supercapacitor (SS) based on WSe₂@graphite composite electrodes. To represent distinct pH environments, three aqueous electrolytes, namely H₂SO₄ (acidic), NaOH (basic), and Na₂SO₄ (neutral), were selected. A range of standard characterization methods, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDX), were employed to validate the successful fabrication and integrity of the supercapacitive electrode. Electrochemical performance was evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS), elucidating the charge storage behaviour of the device at different pH levels. As a result, the fabricated SS device exhibited an impressive electrochemical potential window of 2 V (0 to +2 V) across all electrolytic systems, demonstrating excellent operational stability and pH adaptability. Among the tested electrolytes, the acidic H₂SO₄ electrolyte demonstrated the highest performance, achieving a high areal capacitance of 123.73 mF cm^-2 and an energy density of 68.73 μWh cm^-2 at a current density of 1 mA cm^-2. Furthermore, the device demonstrated reliable cycling stability, retaining approximately 78.69% of its initial capacitance after 5000 consecutive GCD cycles. These results highlight the critical role of electrolyte pH in tailoring supercapacitor performance and provide valuable insights into the design of high-performance, flexible symmetric supercapacitors through strategic electrolyte selection.