The preparation of self-humidifying Nafion/various Pt-containing SiO2 composite membranes and their application in PEMFC

Various Pt-containing silica nanoparticles were successfully synthesized and adopted in the fabrication of Nafion/silica and Nafion/Pt-containing silica composite membranes. X-ray diffraction and X-ray photoelectron spectroscopy analyses for Pt-containing silica nanoparticle were conducted to identify the phase and oxidation state of Pt incorporated onto silica nanoparticles. Transmission electron micrograph analysis shows 2–3nm of Pt nanoparticles on the surface of silica nanoparticle. Water uptakes of Nafion/Pt-containing silicas and Nafion/silica composite membranes were measured. All these composite membranes show higher water uptakes than that of casting Nafion membrane. In addition, S-Pt/SiO2 and Pt-S/SiO2 composite membranes show a little higher water uptake than that of Nafion/Pt/SiO2 composite membrane due to hydrophilic sulfonic group. The cell test using various MEAs shows that under zero humidity, Nafion/S-Pt/SiO2 composite membrane shows 0.45A/cm2 at 0.6V and even comparable to that of casting Nafion membrane under 100% humidity. It is seen that the cell performance was rather decreased with the increase of Pt-containing silica content due to water flooding and/or electron loss due to the electrical conduction transfer network formed by too much Pt within the membrane. Finally, in case of sulfonation, the order of sulfonation seems to be critical. ► SiO2, Pt/SiO2, Pt-S/SiO2 and S-Pt-SiO2 nanoparticles were successfully synthesized. ► Nafion composite membranes using these inorganic nanoparticles were fabricated. ► Under no humidity, Nafion/S-Pt/SiO2 composite membrane shows excellent performance. ► The order of sulfonation is critical for cell performance under zero humidity. ► Electron loss due to electrical conductive network is related to Pt in membrane.