Preparation of Sulfonated Cross-Linked Films for Proton Exchange Membranes (PEMs) Through a Curing Process

Raw-poly(n-butyl acrylate (BA)-sodium styrene sulfonate (SS)-neopentyl glycol diacrylate (NPGDA)) (raw-PBSN) films were prepared through a curing process from various BA/SS/NPGDA mixtures (BSN mixture). Sulfonation of the raw-PBSN films was performed via a pretreatment process. As a result, light-brown sulfonated PBSN (SPBSN) films with a thickness of 80 ~ 95 μm were obtained. The ion exchange capacity (IEC), proton conductivity (PC), swelling ratio (SR), and water uptake (WU) of these specimens were improved with an increase in the content of SS within the SPBSN matrix. The SPBSN 25 wt%, SPBSN 30 wt% and SPBSN 35 wt% films containing corresponding SS contents of 25 wt%, 30 wt% and 35 wt%, which are much higher IEC values compared to that of Nafion^® 117. Specifically, the PC value of the SPBSN 35 wt% film was approximately 0.211 S/cm, nearly 22.6% higher than that of Nafion^® 117 (0.172 S/cm) at a temperature of 80 °C and relative humidity (RH) of 100%. A fourier transform infrared spectroscopy (FT-IR) analysis was conducted to verify the sulfonation of the raw-PBSN films. A transmission electron microscope (TEM) analysis served to investigate the hydrophilic domain images of the SPBSN films.