Sulfonated Poly(ether sulfone)-Coated and -Blended Nafion Membranes with Enhanced Conductivity and Reduced Hydrogen Permeability

Nafion, as a perfluorosulfonic acid (PFSA)-based polymer, is a key material that contributes to the commercialization of proton exchange membrane fuel cells (PEMFCs). The high dependence on relative humidity (RH) of Nafion or other PFSA membranes for proton conduction, together with its decreased mechanical and dimensional stability and high fuel (H2) crossover at the cell operating temperatures (80 °C or above), however, remain issues that have yet to be solved. In the current work, thin sulfonated poly(arylene ether sulfone) (sPES)-coated Nafion membranes (sPES-c-Nafions) are developed, for the first time, by simply spin-coating the sPES solution onto a Nafion membrane, and the results are compared with the sPES-blended Nafion counterparts. The sPES-c1-Nafion demonstrates a very high proton conductivity of 223.3 mS cm–1 (80 °C) and a very low hydrogen permeability, a 41% reduction compared to that of Nafion-212, together with improved mechanical and dimensional stabilities compared to Nafion-212. The developed membrane also shows excellent cell performance (i.e., with a current density of 1.56 A cm–2 and a peak power density of 1.20 W cm–2 at 0.6 V potential in the actual operating conditions of PEMFCs).