Influence of Fluorocarbon- and Hydrocarbon-Based Hybrid Surfactant on Properties of PFSA/ePTFE-Reinforced Composite Membrane for PEMFC Application

Polymer electrolyte membrane is a crucial component, significantly influencing performance and durability in proton exchange membrane fuel cells (PEMFCs). To improve sustainable PEMFC performance under alternating wet/dry conditions, reinforced composite membranes (RCMs) have been suggested that expanded polytetrafluoroethylene (ePTFE) is incorporated into fabrication of perfluorosulfonic acid (PFSA) membrane. However, due to repulsion between hydrophilic PFSA and hydrophobic ePTFE, incomplete impregnation in the RCM resulted in low proton conductivity and high gas permeability in a single cell. To overcome this problem, surfactants are able to not only reduce the repulsion between ePTFE and PFSA, but also improve the electrochemical properties of RCMs. In this study, fluorocarbon- and hydrocarbon- (CF-CH)-based hybrid surfactants were synthesized and introduced into PFSA solution. With the addition of CF-CH hybrid surfactants, the ionomer solution exhibited lower contact angle on ePTFE, resulting in higher ion conductivity of RCMs. Notably, the improvement of impregnation in RCMs was investigated using Fourier transform infrared spectroscopy (FTIR), focused ion beam-scanning electron microscopy (FIB-SEM), and energy dispersive X-ray spectroscopy (EDS). In a single cell, the RCM with 1.0 mmol/L of CF-CH hybrid surfactant (HS-RCM) achieved a current density of 1.210 A cm^-2 at 0.6 V and maximum power density of 740 mW cm^-2 which is 13.8 % higher than pristine RCM (p-RCM). The accelerated stress test (AST) demonstrated that the durable properties of HS-RCM were maintained for 168 hours under alternating wet/dry conditions. Overall, the improved cell performance and durability of HS-RCMs is a promising potential for application in PEMFCs.