Inorganic–organic membranes based on Nafion, [(ZrO2)·(HfO2)0.25] and [(SiO2)·(HfO2)0.28]. Part I: Synthesis, thermal stability and performance in a single PEMFC

This work reports the preparation, characterization and test in a single fuel cell of two families of hybrid inorganic-organic proton-conducting membranes, each based on Nafion and a different “core-shell” nanofiller. Nanofillers, based on either a ZrO2 “core” covered with a HfO2 “shell” (ZrHf) or a HfO2 “core” solvated by a “shell” of SiO2 nanoparticles (SiHf), are considered. The two families of membranes are labelled [Nafion/(ZrHf)x] and [Nafion/(SiHf)x], respectively. The morphology of the nanofillers is investigated with high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX) and electron diffraction (ED) measurements. The mass fractions of nanofiller x used for both families are 0.05, 0.10 or 0.15. The proton exchange capacity (PEC) and the water uptake (WU) of the hybrid membranes are determined. The thermal stability is investigated by high-resolution thermogravimetric measurements (TGA). Each membrane is used in the fabrication of a membrane-electrode assembly (MEA) that is tested in single-cell configuration under operating conditions. The polarization curves are determined by varying the activity of the water vapour (aH2O) and the back pressure of the reagent streams. A coherent model is proposed to correlate the water uptake and proton conduction of the hybrid membranes with the microscopic interactions between the Nafion host polymer and the particles of the different “core–shell” nanofillers.

► Two new “core–shell” nanofillers, [(ZrO2)·(HfO2)0.25] and [(SiO2)·(HfO2)0.28] were prepared. ► The nanofillers were dispersed into Nafion to obtain two series of proton-conducting membranes. ► The two nanofillers affect differently the thermomechanical features and the fuel cell performance of the samples. ► The data are rationalized in a model correlating the different Nafion-nanofiller interactions with the experimental trends.