Stability of sulfonated poly ether ether ketone nanocomposite membrane for direct methanol fuel cell application

Abstract

In this study, the stability of sulfonated poly ether ether ketone (SPEEK) nanocomposite membrane against the radical attack during direct methanol fuel cell (DMFC) operation was elucidated by the Fenton reagent test. The nanocomposite membrane was soaked in the Fenton reagent solution with 0.8, 3, 12, and 50 ppm iron salts concentration for 6, 12, 24, 48, and 96 hours, respectively at room temperature. Pristine SPEEK and Nafion® 117 membranes were used as control samples. The results indicate that the presence of Cloisite® inorganic particles can improve the stability of SPEEK nanocomposite membrane against the radical attack and allowed the nanocomposite membrane to maintain its weight comparable to Nafion® 117 membrane up to 48 hours of testing. The Fourier transform infrared spectroscopy characterization combined with density functional theory study showed that both the C?O?C and ?SO3H bonding with phenylene ring, and hydrogen bonding between the SPEEK, Cloisite®, and 2,4,6-triaminopyrimidine components were the most vulnerable to the radical attack. Loss of these functional groups has caused structural deformation, deterioration of mechanical strength, and changes of hydrophilicity in the SPEEK nanocomposite membrane. Additionally, the changes in its chemical structure have caused its water uptake, proton conductivity, and methanol barrier properties to drop, up to 2 times higher than the Nafion® 117 membrane. However, the selectivity value of the SPEEK nanocomposite membrane (27,037 S·s/cm3) remained higher than the Nafion® 117 membrane (3,292 S·s/cm3) due to the SPEEK nanocomposite membrane’s lower methanol permeability value (2.72×10-7 cm2/s) as compared to Nafion® 117 membrane (2.95×10-6 cm2/s). Based on the correlation graph, the SPEEK nanocomposite membrane is predicted to have 9,800 hours’ lifespans as polymer electrolyte membrane (PEM) in the DMFC system. As a conclusion, this study has proven that the SPEEK nanocomposite membrane has good stability in DMFC harsh environment and suitable to be employed as PEM for high performance and long lifespan DMFC system.