Effect of Sulfonation Level on Sulfonated Aromatic Poly(ether sulfone) Membranes as Polymer Electrolyte for High-Temperature Polymer Electrolyte Membrane Fuel Cells

Sulfonated poly(ether sulfone)s (SPESs) are developed which have different sulfonation level as a polymer electrolyte membrane for high-temperature operation. The sulfonation level of SPESs is calculated by ¹H NMR, and the molecular structure and crystalline structure of SPESs are evaluated by Fourier transform infrared and X-ray diffraction. SPES membranes are thermally stable up to 250 °C. SPES membranes can keep their shapes at 120 °C and 23%RH. Water uptake at 120 °C and 23%RH is 5.7–6.4 wt%, while Nafion 212 shows 2.4 wt%. Proton conductivity measurements of SPESs are carried out from 30 to 120 °C at different relative humidity. With increasing sulfonation level of SPES, proton conductivity increases in all humidity. The proton conductivity obtained from all SPESs is more than 100 mS cm^–1 at 120 °C in high humidity (>90%RH), and high-sulfonation SPES shows higher conductivities than Nafion 212 at 120 °C, 20%RH. (Figure presented.).