Advanced Nafion nanocomposite membrane embedded with unzipped and functionalized graphite nanofibers for high-temperature hydrogen-air fuel cell system: The impact of filler on power density, chemical durability and hydrogen permeability of membrane

Nafion, a perfluorosulfonic acid (PFSA) polymer, is a key electrolyte that has contributed to commercialization of hydrogen-air fuel cells (HAFCs). However, adoption of Nafion membranes in high-temperature (HT) HAFCs remains an unsolved challenge. In this work, sulfonic acid-functionalized, unzipped graphite nanofiber (SO₃H-UGNF) is explored as a potential filler for Nafion to create a composite membrane for HT-HAFCs. The presence of –SO₃H groups in SO₃H-UGNF permits better dispersion of filler and boosts physiochemical, thermomechanical, and electrochemical properties of Nafion/SO ₃H-UGNF membrane compared to bare Nafion, Nafion/GNF, and Nafion/UGNF membranes. A range of concentrations of SO₃H-UGNF (0.5, 1, or 1.5 wt%) are added to Nafion matrix to establish an optimal content for enhancing proton conductivity at 100, 50, and 18% relative humidity (RH). The optimized Nafion/SO₃H-UGNF (1 wt%) membrane achieved a power output of 0.226 W cm^-2 and durability of over 129 h at 120 °C with 18% RH, which represents one of the best performances among reported Nafion-based membranes in HT-HAFCs. The hydrogen permeability, mechanical strength, and morphology of Nafion/SO₃H-UGNF membrane were retained reasonably after durability test in HT-HAFC. This study provides valuable insights for design and optimization of potential Nafion composites for HT-HAFCs.