AbstractThis work describes the effect of sulfuric acid protonation on the properties of SPOD-DPE membranes using FT-IR and impedance spectroscopic analyses. The IR spectra showed the protonation of nitrogen atoms from oxadiazole rings, with a broad band complex in the region 3 000–2 100 cm1 with two centered peaks at 2 590 and 2 440 cm1. The S––O characteristic
absorption bands in SPOD-DPE and sulfuric acid were specially studied in the region of 1 800–900 cm1. The
band shifts are associated to the interaction between acid groups and oxadiazole ring nitrogen atoms. The IR spectra evidenced the presence of three absorption species (HSO4, SO2 4 and free H2SO4) depending on the sulfuric acid concentration. For the protonated SPOD-DPE membranes, a proton conductivity around 10 mScm1 was reached at 50 8C.