Electrochemical analysis of flexible symmetric supercapacitors using WSe2@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.