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

Abstract

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 ZrO 2 "core" covered with a HfO 2 "shell" (ZrHf) or a HfO 2 "core" solvated by a "shell" of SiO 2 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 (a H2O) 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 "coreeshell" nanofillers.

New nanocomposite proton conducting membranes based on a core–shell nanofiller for low relative humidity fuel cells

“…30 The fourth mass elimination, detected between 400-500 uC range, is due to the decomposition of the fluorocarbon chains of the polymer matrix. [22][23][24][28][29][30]35 The thermal stability of the PTFE chains in the presence of ZrTa is higher than in pristine Nafion. Above 600 uC, the mass residue is related to the amount of the inorganic moiety present in bulk membranes.…”

“…4 inset a, is associated with the degradation of -SO 3 H groups and is in agreement with previous studies. [28][29][30]35 The filler has a slight stabilizing effect on the -SO 3 H groups in the composite membranes as compared to pristine Nafion. The weight loss observed between 300 and 380 uC (Fig.…”

“…4 inset b) is associated with the thermal degradation of the polyether side chains. 23,24,[28][29][30]35 In contrast to the filler's stabilizing effect on the -SO 3 H groups, ZrTa tends to decrease the thermal stability of the polyether side groups likely due to the catalytic effect of the transition metal oxides. 30 The fourth mass elimination, detected between 400-500 uC range, is due to the decomposition of the fluorocarbon chains of the polymer matrix.…”

“…23,24,[28][29][30]35 In contrast to the filler's stabilizing effect on the -SO 3 H groups, ZrTa tends to decrease the thermal stability of the polyether side groups likely due to the catalytic effect of the transition metal oxides. 30 The fourth mass elimination, detected between 400-500 uC range, is due to the decomposition of the fluorocarbon chains of the polymer matrix. [22][23][24][28][29][30]35 The thermal stability of the PTFE chains in the presence of ZrTa is higher than in pristine Nafion.…”

“…Of the group IV and period VI oxoclusters previously investigated, [22][23][24]28 32 The preparation of the nanofiller based on ZrO 2 and Ta 2 O 5 , indicated as ZrTa, is part of an effort to produce a ''chemical core-shell'' nanofiller and subsequently elucidate the effect of its chemistry and surface properties on the structure, properties and fuel cell performance of the resulting hybrid inorganic-organic membranes. 30 In addition, the water uptake, the thermal and structural properties will be examined. Finally, the performance of the hybrid membrane with 12.8 wt% of nanofiller will be tested in a single cell configuration at different reagent back pressures and hydration degrees.…”