Lignin/zirconium phosphate/ionic liquids-based proton conducting membranes for high-temperature PEM fuel cells applications

This work reports the fabrication of lignin-zirconium phosphate-based membranes modified with ionic liquids (ILs) for high-temperature operation in proton exchange membrane (PEM) fuel cells. The Lignin-modified membranes demonstrated a noticeable enhancement in proton conductivity as opposed to pure zirconium phosphate-based membranes by one order of magnitude at room temperature, i.e., from 10−4 to 10−3 S/cm, respectively. Further enhancements in conductivity were observed upon the addition of ionic liquids. Among the three ILs evaluated in this work, the Hexyl-based ionic liquid resulted in the highest conductivity at room temperature, 10−1 S/cm. The membranes showed considerably high anhydrous proton conductivities in the range of 10−3–10−4 S/cm at 150 °C. Additional characterization tests showed considerable water uptake enhancement, high thermal stability, and changes in particles’ morphology. The findings of this work show the suitability of these membranes for high-temperature operation in proton exchange membrane fuel cells.