Effect of sulfonating agent in the properties of styrene copolymers for PEMFC membranes

Two different sulfonating agents: sulfuric acid (S) and acetyl sulfate (AcS) were evaluated for chemical modification of poly (styrene-co-butyl acrylate) (StBuA) copolymer, as low-cost membranes. The reaction was carried out by direct sulfonation during 2-5 h of sul-fonation time. FTIR confirmed sulfonation through the presence and widening of the several SO3H characteristic absorption bands. The molecular weight decreased after sul-fonation, compared with pristine StBuA. TGA thermal analysis showed stability over 150 C with residues suggesting crosslinking and a glass transition (Tg) enhanced. Even with higher Tg values, sulfonated copolymers became flexible, as seen by their lower complex modulus (E*). Ion exchange capacity (IEC) ranged from 0.91 to 1.53 meq g-1 and degree of sulfonation (DS) from 7 to 40%. The proton conductivity for sulfonated membranes exhibited similar or higher to Nafion membrane, particularly for S-4h membranes. A Grotthuss mechanism is envisaged for AcS and vehicular mechanism for S membranes.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study evaluated the chemical modification of poly (styrene-co-butyl acrylate) copolymer using sulfuric acid and acetyl sulfate as low-cost membranes. The results showed that the sulfonated membranes had lower complex modulus and higher proton conductivity.