A composite proton exchange membrane with a three-dimensionally-reinforced hydrogen bonding network for durable hydrogen fuel cells

Abstract

Expanded polytetrafluoroethylene (e-PTFE) reinforced perfluorosulfonic acid (PFSA) is the predominant proton exchange membrane (PEM) for hydrogen fuel cells. However, the difference in interfacial properties between PFSA and e-PTFE significantly decreases the proton conduction efficiency and durability of the PEM. In this study, the polyphenolamine treatment method (TA) is employed to effectively enhance the hydrophilicity and interfacial compatibility of e-PTFE, as well as to functionalize the surface of the free radical scavenger ZrO₂ filler. The surface of the modified e-PTFE and ZrO₂ is rich in polar phenolic hydroxyl groups and amino groups, which effectively enhance the three-dimensional interface compatibility of the e-PTFE/PFSA reinforced composite membrane (RCM), and improve the proton conductivity by establishing a three-dimensionally-reinforced hydrogen bonding network. The proton conductivity of the RCM is 0.203 S cm⁻¹ at 80 °C, and the tensile strength is 50.7 MPa. The peak power density of the hydrogen fuel cell based on the composite membrane is 1.46 W cm⁻² at 80 °C and 50% RH. Moreover, the durability of the composite membrane is considerably improved by the redox properties of the surface functional groups of e-PTFE and the valence-changing properties of ZrO₂. Following a 72-hour Fenton reaction, the mass loss of the TA@ZrO₂/e-PTFE RCM was found to be only 13.5%. The accelerated durability test indicates that the TA@ZrO₂/e-PTFE RCM can still provide a current density of 1.3 A cm⁻² after 5500 dry/wet cycles at 0.55 V.