Abstract

The PEEK was sulfonated via electrophilic substitution by treating it with concentrated sulfuric acid (98%), resulting in the introduction of sulfonic acid groups (–SO3H) onto the polymer backbone. Graphene nanosheets (GNS) and tin oxide (SnO2) nanoparticles were synthesized via a hydrothermal method, leveraging their efficacy as radical scavengers. The GNS/SnO? materials were then incorporated into a SPEEK polymer matrix, resulting in the composite membranes with superior proton conductivity and greater durability, owing to the combined effects of the GNS/SnO? integration. In addition, the membranes were evaluated for their physicochemical, thermal, and mechanical characteristics, along with their proton conductivity. Under the conditions of 80°C and 95% of relative humidity, the proton conductivity of the 1 wt.% GNS/SnO2@SPEEK nanocomposite membrane was 0.196 S/cm, surpassing the pristine SPEEK membrane, which recorded a lower value of 0.102 S/cm.The membrane strength was assessed through the oxidative stability tests, revealing that the 1 wt.% GNS/SnO2@SPEEK membrane outperformed the unmodified membrane. These impressive properties highlight the potential of GNS/SnO2-based PEMs as the promising candidates for the next-generation PEMFC technologies. © 2025 Informa UK Limited, trading as Taylor & Francis Group.