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 Ă— 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)
Toward Pt-Free Anion-Exchange Membrane Fuel Cells: Fe–Sn Carbon Nitride–Graphene Core–Shell Electrocatalysts for the Oxygen Reduction Reaction
We report on the
development of two new <i>Pt-free</i> electrocatalysts (ECs)
for the oxygen reduction reaction (ORR) process
based on graphene nanoplatelets (GNPs). We designed the ECs with a <i>core–shell</i> morphology, where a GNP <i>core</i> support is covered by a carbon nitride (CN) <i>shell.</i> The proposed ECs present ORR active sites that are not associated
with nanoparticles of metal/alloy/oxide but are instead based on Fe
and Sn subnanometric clusters bound in <i>coordination nests</i> formed by carbon and nitrogen ligands of the CN <i>shell</i>. The performance and reaction mechanism of the ECs in the ORR are
evaluated in an alkaline medium by cyclic voltammetry with the thin-film
rotating ring-disk approach and confirmed by measurements on gas-diffusion
electrodes. The proposed GNP-supported ECs present an ORR overpotential
of only ca. 70 mV higher with respect to a conventional Pt/C reference
EC including a XC-72R carbon black support. These results make the
reported ECs very promising for application in anion-exchange membrane
fuel cells. Moreover, our methodology provides an example of a general
synthesis protocol for the development of new <i>Pt-free</i> ECs for the ORR having ample room for further performance improvement
beyond the state of the art