Ionic Highways from Covalent Assembly in Highly Conducting and Stable Anion Exchange Membrane Fuel Cells

A major challenge
in the development of anion exchange membranes
for fuel cells is the design and synthesis of highly stable (chemically
and mechanically) conducting membranes. Membranes that can endure
highly alkaline environments while rapidly transporting hydroxides
are desired. Herein, we present a design using cross-linked polymer
membranes containing ionic highways along charge-delocalized
pyrazolium cations and homoconjugated triptycenes. These ionic highway
membranes show improved performance. Specifically, a conductivity
of 111.6 mS cm–1 at 80 °C was obtained with
a low 7.9% water uptake and 0.91 mmol g–1 ion exchange
capacity. In contrast to existing materials, ionic highways produce
higher conductivities at reduced hydration and ionic exchange capacities.
The membranes retain more than 75% of their initial conductivity after
30 days of an alkaline stability test. The formation of ionic highways
for ion transport is confirmed by density functional theory and Monte
Carlo studies. A single cell with platinum metal catalysts at 80 °C
showed a high peak density of 0.73 W cm–2 (0.45
W cm–2 from a silver-based cathode) and stable performance
throughout 400 h tests.