The possibility of a Nafion membrane undergoing an irreversible
loss of proton conductivity when hot-pressed at high
temperatures is also investigated. Bare Nafion 115 membranes
in Hþ-form were hot-pressed under the same conditions as
those adopted for the MEA fabrication discussed in this section.
After hot-pressing at five different temperatures, all
membranes were kept in de-ionized water for 48 h at room
temperature to allow them to retain their fully hydrated state,
and then their proton conductivities were measured using a
conductivity cell.