2-Mercaptoethanesulfonic Acid as an Effective Free-Radical Scavenger in Perfluorosulfonic Acid Membrane-Based Polymer Electrolyte Membrane Fuel Cells

Abstract

Ceria nanoparticle-based free-radical scavengers for the mitigation of oxidative damage in perfluorosulfonic acid (PFSA)-based polymer electrolyte membrane fuel cells (PEMFCs) suffer from the drawbacks of lowered protonic conductivity and leaching in the acidic environment of a PEMFC. As an alternative to ceria, here we demonstrate that oxidative damage can be mitigated by functionalization of Nafion with 2-Mercaptoethanesulfonic acid (MESA) in different (0.1–1.0 wt%) ratio. The spectroscopic investigation indicated successful functionalization of MESA over the Nafion chain and resulting Nafion-MESA composite membranes displayed improved hydration and swelling behavior, and thermal and mechanical properties. At ≤60 °C (95% relative humidity), the protonic conductivity of composite membranes was higher than/equivalent to that of pristine Nafion membrane; however, at ≥70 °C it was ∼6%–8% lower. At 80 °C, conductivity of Nafion-MESA-0.1 wt%, Nafion-MESA-0.25 wt%, pristine Nafion, and state-of-the-art Nafion-CeO2−1wt% membranes were 1.72 × 10−1, 1.67 × 10−1, 1.8 × 10−1, and 1.6 × 10−1 S∙cm−1, respectively. The fluoride emission rate value for the same membranes were 0.30, 0.17, 1.39, and 0.27 mg∙g−1, respectively, thus indicating that Nafion-MESA membranes can substitute the ceria-based membranes as a chemically stable membrane electrolyte in PEMFCs.