Quaternized poly (ether ether ketone)s doped with phosphoric acid for high-temperature polymer electrolyte membrane fuel cells

Abstract

Quaternized poly(ether ether ketone)s (QPEEKs), which were aminated by trimethylamine (TMeA), triethylamine (TEtA), tripropylamine (TPrA) and 1-methylimidazole (MeIm), were prepared and used as phosphoric acid (PA)-doped high-temperature proton exchange membranes. These QPEEK membranes showed high glass transition temperature (T_g was higher than 483 K) and high thermal stability (T_5% was higher than 486 K). The tensile strengths of these QPEEK membranes were higher than 60 MPa. The PA-doped im-QPEEK, which was aminated by MeIm, had the highest W_doping (159 wt%) and proton conductivity (0.05 S cm⁻¹ at 473 K). For the other three PA-doped QPEEK membranes, the W_doping and proton conductivity decreased with the increase of the length of trialkyl side chains on quaternary ammonium groups. According to our study, the PA absorbing ability was subjected to the structures of quaternary ammonium groups instead of the basicities of quaternary aminating reagents. All PA-doped membranes had great oxidative stability and could last for more than 5 h in 3 wt% H₂O₂, 4 ppm Fe²⁺ Fenton solution at 353 K.