Synthesis and Characterisation of Sulphonated Poly(arylene sulphone) Terpolymers with Triphenylphosphine Oxide Moieties for Proton Exchange Membrane Fuel Cells

Abstract

For application in fuel cells, a series of sulphonated poly(phenylene sulphone) terpolymers with triphenylphosphine oxide moieties as constitutional units in the polymer backbone have been prepared. The synthesis of the terpolymers represents a two‐step process including: (i) an aromatic nucleophilic substitution polycondensation of three difluoro monomers with varying ratios, i.e. 3,3′‐disulphonate‐4,4′‐difluorodiphenylsulphone, 4,4′‐difluorodiphenylsulphone and bis(4‐fluorophenyl)phenyl phosphine oxide (BFPPO), with 4,4′‐thiobisbenzenethiol yielding sulphonated poly(phenylene sulphide) terpolymers (sPPSPO) and (ii) their following oxidation with hydrogen peroxide in acidic solution to yield sulphonated poly(phenylene sulphone) terpolymers (sPPSO2PO). The structures and molecular compositions were confirmed by 1H and 13C NMR spectroscopy. The ion exchange capacity (IEC) was adjusted at will choosing the appropriate ratio of sulphonated and unsulphonated monomers. Terpolymers with 1.72 ≤ IEC ≤ 2.32 have been obtained. Sulphonated poly(arylene) ionomers containing only sulphone (–SO2–) linkages and phosphine oxide (–PO–) units rather than ether or sulphide in the backbone reveal a high thermal and oxidative stability. Membranes were cast either from dimethylformamide (DMF) or from dimethyl sulphoxide (DMSO) solutions. For all terpolymers some general characteristic trends were observed, such as an increase of the proton conductivity with increasing IEC, water uptake and temperature. The series of sPPSO2PO membranes offered high conductivities at high humidification, however, their performance strongly depends on the relative humidity.The mechanical properties of sulphonated poly(phenylene sulphone)s have been considerably improved by means of terpolymerisation with phenylene oxide moieties. Even under high humidification the terpolymers form clear, flexible membranes the stress at break of some membranes exceeds that of Nafion® under the same conditions by 40%.

Sulfonated dendrimer‐ and hyperbranched polyglycerol‐PBIOO® blend membranes for fuel cells

“…This result could be due to the different microstructure developed during film formation. All of the samples showed conductivity values that were slightly lower than that of Nafion ® 117 at high RH and 25 °C, although at low RH the conductivities were significantly lower.…”

“…The proton conductivity increased with increasing RH, i.e., with increasing hydration. The reason for this dependence seems to be that the connectivity between sulfonic acid groups necessary for proton transport decreases at low hydration levels . The different nature of the acid component also had a marked influence on the proton conductivity.…”

“…The reason for this dependence seems to be that the connectivity between sulfonic acid groups necessary for proton transport decreases at low hydration levels. [47][48][49][50] The different nature of the acid component also had a marked influence on the proton conductivity. Whereas the conductivity of membranes prepared from dendrimer 4 decreased in an almost linear manner with RH ( Fig.…”

Proton Conducting Phase‐Separated Multiblock Copolymers with Sulfonated Poly(phenylene sulfone) Blocks for Electrochemical Applications: Preparation, Morphology, Hydration Behavior, and Transport

“…As fuel cell membranes are exposed to harsh conditions ( T > 100 °C, extreme RH variations, possible formation of HO• or HO 2 • radicals at the electrodes),40 oxidative and hydrolytic stability plays an important role in their application. Polymers with sulfide (‐S‐) or ether (‐O‐) groups in the main chain are less stable than polymers with electron‐withdrawing sulfone groups (‐SO 2 )12, 27 and their application in fuel cells is problematic 41. To increase the oxidative and hydrolytic stability of the hydrophilic blocks we have oxidized the sulfonated poly (phenylene sulfide sulfone) precursors (SS v ) to sulfonated poly (phenylene sulfone)s (SU v ) (Scheme ).…”

“…However, the performance at high temperature and low relative humidity (RH) was always found to be the same or worse than for PFSA membranes,6–10 which is mainly explained by microstructural differences between these two families of membrane material 6, 11. Some partially sulfonated random copolymers already show improved conductivities over PFSA membranes at high RH, but this is lost at low RH 12…”