Insights into the amine-end-terminated fluorophore based zwitterionic poly(methyl methacrylate) quasi-solid electrolyte for flexible supercapacitors

Abstract

Zwitterionic polymethyl methacrylate (PMMA)-based electrolyte membranes were developed using a straightforward blending method for supercapacitor applications. An amine end-terminated rhodamine derivative was synthesized from rhodamine 6G. Structural identification and modifications in the rhodamine-doped PMMA were investigated using FT-IR and NMR. The peaks at 1.3 (–CH₃), 2.3 (–CH₃), 2.3–2.7 (–CH₂) and 3.5 ppm (–OCH₃) confirmed the functional groups of PMMA, while notable peaks at 1.06, 2.1, and 2.5 ppm revealed the alkyl chains from rhodamine. Interestingly, rhodamine impregnation enhanced the luminescence property of the PMMA membrane, as evidenced by emissions at 542 and 558 nm in the photoluminescence (PL) spectra, attributed to the radiative recombination and defects in the system. Upon incorporating an ionic liquid (IL), the defective-structure emission disappeared, accompanied by a red shift in radiative emission, indicating that the IL integration facilitated defect-free electrolyte formation with an improved voltage window. Further, the IL-containing electrolyte membrane demonstrated enhanced hydrophobicity, with a contact angle of 114.32°, underscoring its suitability for stable electrochemical applications. Electrochemical properties were evaluated using a symmetrical two-electrode system through cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) studies. The specific capacitance values were 68 and 100 F g⁻¹ for the electrolyte with and without IL, respectively. Furthermore, the solid polymer electrolytes exhibited excellent long-term cyclic stability, retaining ∼80 % of their capacity over 5000 GCD cycles at a current density of 2 Ag⁻¹.