Highly stable aprotic ionic-liquid doped anhydrous proton-conducting polymer electrolyte membrane for high-temperature applications

Abstract

Protic ionic-liquid (IL) based polymer electrolyte membranes (PEMs) have been reported for high-temperature fuel cell applications under anhydrous condition. Herein, we report aprotic IL (1-ethyl-3-methylimidazolium ethyl sulfate (EMIES)) and sulfonated poly(ether ether ketone) (SPEEK) based PEMs for fuel cell application under anhydrous condition. Liberated protons from –SO₃H groups (SPEEK) due to ionic interaction with EMIES, were responsible for high conductivity under anhydrous conditions. High ionic interaction between the EMIES and SPEEK led to homogeneous mixing. Prepared SPEEK–IL-70 PEM exhibited 0.57 mS cm⁻¹ conductivity (conductivity of EMIES: 3.445 mS cm⁻¹ at room temperature), which was dramatically increased to 18.94 mS cm⁻¹ at 150 °C under anhydrous condition. This enhancement in conductivity was explained due to the well-connected proton conducting channels formed in the polymer matrix because of good miscibility and interaction with EMIES. High stability and good conductivity of SPEEK–IL composite membranes demonstrated their potential application for high-temperature applications.