Protonation of Sulfonated Poly(4,4′‐diphenylether‐1,3,4‐oxadiazole) Membranes

Abstract

This 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 cm−1 with two centered peaks at 2 590 and 2 440 cm−1. The SO characteristic absorption bands in SPOD‐DPE and sulfuric acid were specially studied in the region of 1 800–900 cm−1. 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 (HSO, SO and free H2SO4) depending on the sulfuric acid concentration. For the protonated SPOD‐DPE membranes, a proton conductivity around 10 mS · cm−1 was reached at 50 °C.magnified image

Proton Conducting Membranes Based on Benzimidazole Sulfonic Acid Doped Sulfonated Poly(Oxadiazole–Triazole) Copolymer for Low Humidity Operation

“…The CN stretching vibrations are observed to produce intense bands at 1,200-1,310 cm -1 , for BiSA should be the intense peak at 1,278 cm -1 [21]. The frequency range of 1,400-1,000 cm -1 comprises also absorptions due to the sulphonic groups [12,18]. The peak at 1,395 cm -1 has been attributed to the SO 2 asymmetric stretching of the sulphonic group covalently bonded to the SPOD-SPT polymer, and shows an increasing intensity with an increasing amount of doping; probably the presence of the doping agent may interrupt the interactions between nitrogen atoms of oxadiazole and triazole rings and hydrogen atoms of the sulphonic group covalently bonded, and therefore increasing the amount of free sulphonic group with respect to the amount of it in the pure SPOD-SPT.…”

“…The copolymer backbone alone has a combination of acidic (-SO 3 H group) and basic sites (basic nitrogen) for effective interaction with protons, water and additional doping molecules. Doping of sulphonated polyoxadiazole with sulphuric acid, analogously to what is usually performed with PBI, has been recently reported to increase the proton conductivity [12]. In this paper, the idea is to dope the sulphonated oxadiazoletriazole copolymers with small amphoteric molecules containing acid and basic groups similar to those forming the polymer background, increasing the possibility of hydrogen bond formation: benzimidazole sulphonic acid (BiSA).…”

“…Our group has reported the doping of sulphonated polyoxadiazole membranes by doping with different concentrations of sulphuric acid and different immersion times in the acid bath. After treating the sulphonated polyoxadiazole membranes with a 1.6 M H 2 SO 4 solution, the measured proton conductivity was around 1 10 -2 S cm -1 at 50 C and 100% relative humidity [12]. The relatively high proton conductivity values for sulphonated polyoxadiazoles and polytriazoles are believed to be due to the availability of well distributed acidic and amphoteric sites for hydrogen bonding.…”

Polymer electrolyte membranes based on p‐toluenesulfonic acid doped poly(1‐vinyl‐1,2,4‐triazole): Synthesis, thermal and proton conductivity properties

“…The proton exchange reactions between triazole and sulfonic acid groups have been reported in an earlier work 20. As far as the characterization by FTIR spectroscopy is concerned, there are basically two spectral regions: 4000–2000 cm −1 and 1800–900 cm −1 that can be related to heterocyclic groups 24. Also for anhydrous PVTrixPTSA electrolytes the same spectral regions were chosen.…”

Preparation and evaluation of sulfonated polyoxadiazole membrane containing phenol moiety for PEMFC application

“…Oxadiazole groups have a well-balanced amphoteric character. In this kind of materials, the proton conducting mechanism is based on a nonvehicular mechanism (Grotthuss mechanism) in which hetero atoms make favorable additional points for proton jumps [27,29,39] and only protons move from point to point without the help of vehicle molecules such as water or non-covalent acid molecules [50].…”