2 research outputs found
Interplay between Composition, Structure, and Properties of New H<sub>3</sub>PO<sub>4</sub>‑Doped PBI<sub>4</sub>N–HfO<sub>2</sub> Nanocomposite Membranes for High-Temperature Proton Exchange Membrane Fuel Cells
Polybenzimidazole (PBI) has become
a popular polymer of choice
for the preparation of membranes for potential use in high-temperature
proton exchange membrane polymer fuel cells. Phosphoric acid-doped
composite membranes of polyÂ[2,2′-(<i>m</i>-phenylene)-5,5′-bibenzimidazole]
(PBI4N) impregnated with hafnium oxide nanofiller with varying content
levels (0–18 wt %) have been prepared. The structure–property
relationships of both the undoped and acid-doped composite membranes
are studied using thermogravimetric analysis, modulated differential
scanning calorimetry, dynamic mechanical analysis, wide-angle X-ray
scattering, infrared spectroscopy, and broadband electrical spectroscopy.
Results indicate that the presence of nanofiller improves the thermal
and mechanical properties of the undoped membranes and facilitates
a greater level of acid uptake. The degree of acid dissociation within
the acid-doped membranes is found to increase with increasing nanofiller
content. This results in a conductivity, at 215 °C and a nanofiller
level <i>x</i> ≥ 0.04, of 9.0 × 10<sup>–2</sup> S cm<sup>–1</sup> for [PBI4NÂ(HfO<sub>2</sub>)<sub><i>x</i></sub>]Â(H<sub>3</sub>PO<sub>4</sub>)<sub><i>y</i></sub>. This renders nanocomposite membranes of this type as good
candidates for use in high temperature proton exchange membrane fuel
cells (HT-PEMFCs)
Influence of Anions on Proton-Conducting Membranes Based on Neutralized Nafion 117, Triethylammonium Methanesulfonate, and Triethylammonium Perfluorobutanesulfonate. 2. Electrical Properties
The electrical properties of a Nafion proton exchange membrane change dramatically when neutralized and then doped with a proton-conducting ionic liquid (PCIL). Broadband electric spectroscopy elucidates the molecular relaxation and polarization phenomena of neutralized Nafion (nN117) doped with triethylammonium methanesulfonate (TMS) and triethylammonium perfluorobutanesulfonate (TPFBu) ionic liquids. These data, coupled with those of part 1 suggest proton conduction mechanisms for both the pure PCILs and in PCIL-doped nN117. At 130 °C, the PCILs have conductivities of σ<sub>TMS</sub> = 1.4 × 10<sup>–2 </sup>S/cm and σ<sub>TPFBu</sub> = 9 × 10<sup>–3 </sup>S/cm, while correspondingly doped nN117 have conductivities of σ<sub>NTMS</sub> = 6.1 × 10<sup>–3</sup> S/cm and σ<sub>NTPFBu</sub> = 1.8 × 10<sup>–3 </sup>S/cm. The pure PCILs show three interfacial polarizations associated with proton transfer mechanisms above the melting point. PCIL-doped nN117 also has three interfacial polarizations that depend on the nanostructure characteristics of the PCIL sorbed within the nN117 polar domains. Below the PCIL melting point, doped nN117 has two dielectric relaxations, α and β, associated with dipolar relaxations involving both the sorbed PCILs and the ionomer matrix. The data indicate a long-range charge transfer process that occurs through proton exchange between cationic clusters. Segmental motion of the polymer chains and the molecular dimensions of the ionic liquid nanoaggregates mediate this charge transfer