Enhancing the performance of SPEEK polymer electrolyte membranes using functionalized TiO2 nanoparticles with proton hopping sites

Abstract

In this work, the application of a sulfonated poly(ether ether ketone) (SPEEK)/amine functionalized titanium dioxide nanoparticle (AFT) composite as a novel membrane in proton exchange membrane fuel cells (PEMFC) was studied. Titanium dioxide (TiO₂) nanoparticles were functionalized by grafting aminopropyl groups through hydrolysis of 3-aminopropyltriethoxysilane (APTES). The influence of the AFT nanoparticles on thermal and mechanical stability, water uptake, dimensional stability and electrochemical properties of the membranes were studied. The grafting of APTES onto TiO₂ nanoparticles improved their dispersion in the SPEEK matrix. The nanocomposite membrane with the optimal amount of AFT nanoparticles, 7.5 wt%, showed a proton conductivity of 0.135 S cm⁻¹ at 80 °C which was 159.6% higher than that of the nanocomposite membrane with 7.5% TiO₂. This can be attributed to their good dispersion and reduction of interparticle separation spacing which creates connected pathways for proton transport. The membrane with 7.5 wt% AFT showed a 40.8% decrease in swelling, a 132.7% increase in conductivity and an 86.7% increment in maximum power density (PD_max) (230 mW cm⁻²) compared with the pristine SPEEK membrane, which indicated its potential application in PEMFCs.