Binary phosphonium ionic liquids induced synergistic modulation of electrochemical performance in polymer electrolytes for dual energy devices

The advancement of cost-effective, efficient and sustainable electrochemical devices has garnered significate interest, leading to an aggressive expansion of research aimed at enhancing their performance across various dimensions, including electrode, electrolytes and even computational perspectives. Ionic liquids infused with polymer electrolytes have emerged as one of the most promising candidates for advanced devices, owing to their high conductivity and electrochemical stability. In this study, we present a binary system comprising a polymer electrolyte and phosphonium ionic liquids (PIL), employing polyethylene oxide (PEO) as host matrix and two phosphonium ionic liquids—specifically, tributylmethylphosphonium iodide (TMPI) and tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (TBMP-TFSI) at various compositions, with the aim of significantly enhancing ionic conductivity and wettability. Electrochemical impedance spectroscopy reveals that the incorporation of a binary ionic liquid (IL) leads to a maximum ionic conductivity of 2.04 × 10⁻³ S/cm. Structural analyses confirmed the optimization of the amorphous phase and segmental motion within the polymer matrix. The optimized polymer electrolyte was subsequently evaluated in an electric double-layer capacitor (EDLC), achieving a specific capacitance of 138 F/g at a scan rate of 10 mV/s. The EDLC achieved a maximum specific discharge capacitance of 109 F/g, with a coulombic efficiency of 90%, an energy density of 17.7 Wh/kg and a power density of 5.4 kW/kg. Furthermore, its application in a dye-sensitized solar cell resulted in a power conversion efficiency of 1.48%. These results demonstrate that the optimized polymer electrolyte exhibits enhanced photovoltaic efficiency in dye-sensitized solar cells (DSSCs) and high capacitive performance in electric double-layer capacitors (EDLCs), thereby illustrating its dual functionality.