New hybrid inorganic-organic proton conducting membranes based on Nafion and a [(ZrO₂)⋅(Ta₂O₅)_0.119] oxide core-shell nanofiller

Abstract

Hybrid inorganic-organic proton-conducting membranes are prepared by a standard solvent casting procedure. Nafion^® is used as the host polymer and [(ZrO₂)⋅(Ta₂O₅)_0.119] “core-shell” nanoparticles (d ~ 10-50 nm) are incorporated as the nanofiller. This filler is characterized by a “core” of ZrO₂ nanoparticles covered by a Ta₂O₅ “shell”. The mechanical properties of the resulting hybrid membranes determined by dynamic mechanical analysis are better than those of pristine Nafion. The elastic modulus of the hybrid membranes with a filler content greater than 5 wt% is at least 1 MPa up to 200°C, while pristine Nafion undergoes an irreversible elongation at 160°C. The hybrid membranes are characterized by promising conductivities above 115°C (7.5×10^-2 S⋅cm^-1 for 9 wt% nanofiller vs. 3.3×10^-2 S⋅cm^-1 for pristine Nafion), as determined by broadband electric spectroscopy. The single fuel cell performance at low levels of hydration of the best-performing hybrid membrane (9 wt% nanofiller) is better than that of pristine recast Nafion. The maximum power densities yielded by the MEAs fabricated with pristine Nafion and the hybrid membrane are 0.026 and 0.108 W⋅cm^-2, respectively, at 85°C, a_H2O = 0.13, a reagent back pressure = 1 bar and using pure oxygen as the oxidant.