Proton-conducting (blend) membranes based on sulfonated/phosphonated and basic polymers

Abstract

Aiming at new proton-conducting membranes, this thesis deals with the syntheses and characterizations of highly sulfonated poly(arylene sulfides) and other polysulfides for application as polymer electrolytes. The study focuses mainly on the analysis of the polymer structures that would improve the conductivity of current proton conducting membranes while maintaining their mechanical stability. In a first step, several polymers are obtained from which poly(arylene sulfide)s polymers look more promising for further functionalization. They are obtained by using mild reaction conditions of a polycondensation reaction between 4,4 ́-thiobisbenzenethiol (TBBT) and decafluorobiphenyl. Optimization of this reaction allows for the obtainment of higher molecular weights than the ones reported in the literature. In a second step, poly(arylene sulfides) were phosphonated and sulfonated by a nucleophilic aromatic substitution (SNAr) displacement reaction of the fluorine atoms of the fluorinated polymer sub-units using different agents. Highly sulfonated polymers were obtained when using sodium 3-mercapto-1-propanesulfonate and resulted in water soluble ionomers. Kinetic studies of this reaction were performed and several new sulfonated poly(arylene sulfides) were obtained. Finally, stable polymer electrolyte membrane (PEM) with enhanced mechanical and chemical stability were obtained by blending these obtained ionomers with polybenzimidazole (PBIOO). These membranes were further characterized and in the best case a PEM with new sulfonated ionomer showed a conductivity 40 % higher than Nafion 212, used as a golden reference material. The best performing PEM’s obtained were further used in an electrolytic cell being part of eSCALED, a H2020 (MSC-ITN-2017. GA# 765376) European project which aim is to obtain a device that does the artificial photosynthesis in a more efficient way than the current devices.