• Results and discussion
• The often used membranes for current PEMFC technology are
Nafion® membrane, because of its robust structure and
excellent proton conductivity in the hydrated state.
• However, the drastic decrease in the proton conductivity at
low relative humidity limits the operating temperature of fuel
• If the membrane keeps in hydrate state during the operation of
PEMFCs at elevated temperature, the increased pressure
required by the system could offset the benefits arisen from
the high tolerance to impurity of fuel gas.
• A number of efforts have been demonstrated that modified
Nafion® membrane by incorporating hygroscopic inorganic
nanoparticles such as SiO2, TiO2, and ZrO2 can improve water
retention ability and enhance proton conductivity.
• Nafion® solution
Contains 5 wt% of perfluorosulfonate resin (H+ form) and 95 wt% of
isopropanol/water mixture (10:9 weight ratios)
• Tetraethyl Orthosilicate
• N-methyl-2-pyrrolidone (NMP)
Nafion® solutions used in the study were prepared by dissolving Nafion® resin in NMP,
which was obtained by solvent evaporation of the purchased Nafion® solution under
vacuum at 60 ◦C.
The desired quantity of precursor solutions was added dropwise to the Nafion® solution
under vigorous stirring in an inert nitrogen atmosphere at 80 ◦C.
After desired amount of 2M HCl solution was added, the mixture was continuously stirred
for 1 h at 80 ◦C and allowed to cool down to room temperature.
After addition of desired amount of de-ionizedwater, the mixture was then continuously
stirred for another 8 h to complete condensation of precursors and a clear sol containing
hybrid Nafion®–metal oxide nanoparticles was obtained.
The hybrid sol was first placed in a Petri dish, followed by the solvent evaporation
at 100 ◦C for 8 h and then heat-treated at 150 ◦C under vacuum for 3 h.
The formed membranes were than treated using a standard procedure at 80 ◦C for
30min in 5% H2O2 solution, in deionized water, in 0.5M H2SO4 solution, and finally
in de-ionizedwater again.
For comparison, pure Nafion® membrane was preparedand treated using the same
procedure without addition ofprecursors. Thickness of prepared membranes is about
Results and discussion
TEM and EDS
Fig.1.TEM micrographs of Nafion®–SiO2 (a) and Nafion®–ZrO2 (b) hybrid dispersions and energy dispersive
spectra for one particles in TEM micrographs of Nafion ®–SiO2 (c) and Nafion®–ZrO2 (d). The insert
picture in (b) is selected area electron diffraction pattern.
c. recast Nafion®
Fig.2. XRD patterns for nanocomposite membranes: Nafion®–zirconia (a),
Nafion®–silica (b) and recast Nafion® membrane (c).
Fig.3. Water uptake of formed membranes as a function of relative humidity at100 ◦C: Nafion®–zirconia
membrane (triangles), Nafion®–silica membrane (circles), and recast Nafion® membrane (squares). Solid
lines are guide to eyes.
Fig.4. Tensile strength of formed membranes with 5% elongation at different
humidification states: fully hydrated (black) and dry state (gray).
Fig.5. Proton conductivity of Nafion®–zirconia membrane at 100 ◦Cwithout external
humidification as a function of time. The zirconia content is 5% in weight.
Fig.6. Proton conductivities of the formed membranes as a function of temperature without
external humidification: Nafion®–zirconia membrane (triangles), Nafion®–silica membrane
(circles), and recast Nafion® membrane (squares). Solid lines are guide to eyes.
• The formed Nafion®–metal oxide nanocomposite
membranes show enhanced water retention ability and
higher proton conductivity compared to recast pure
NafionR membrane at all measured temperature range.
• Although the proton conductivity of the composite
membrane decreases with increasing temperature,
Nafion®–ZrO2 composite membrane is close to 0.01 S
cm−1 at 100 ◦C without external humidification.
• Thus, the hybrid membrane developed here has the
potential for PEMFC applications at elevated