Preparation of Nafion/various Pt-containing SiO2 composite membranes sulfonated via different sources of sulfonic group and their application in self-humidifying PEMFC

Abstract

Pt nanoparticles were successfully deposited onto SiO2 nanoparticles sulfonated by different chemical sources such as H2SO4, CH3SO3H, Na2SO4, and HSO3Cl and denoted as Pt-HS/SiO2, Pt-CS/SiO2, Pt-NS/SiO2 and Pt-SS/SiO2, respectively. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) analyses for Pt-containing sulfonated SiO2 nanoparticles were conducted to identify the phase, oxidation state of Pt incorporated and the existence of –SO3+ on SiO2 nanoparticles. Transmission electron microscope analysis shows 2–4nm of Pt nanoparticles on the surface of SiO2 nanoparticle. The proton conductivities of various membranes are highly consistent with metallic Pt and –SO3+ contents based on XPS analysis. The membrane electrolyte assembly (MEA) fabricated with Nafion/Pt-NS/SiO2 composite membrane showing the smallest Pt particle size and excellent dispersion shows the best cell performance under zero humidity, following the order of Pt-NS/SiO2>Pt-HS/SiO2>Pt-CS/SiO2>Pt-SS/SiO2. It also shows that the MEA fabricated with Nafion/Pt-NS/SiO2 composite membrane shows the least decrease by 5.7% in open circuit voltage with relative humidity while that for Nafion/Pt-CS/SiO2 composite membrane is the largest by 15.3%. The results suggest that Pt particle size, its dispersion, metallic Pt and –SO3 contents are critical and quite different with chemical source for sulfonation, affecting the cell performance.