Reporter:Wen-Cheng Lin Teacher:Wei-Tung Liao

Outline• Introduction

• Materials

• Experimental

• Results and discussion

• Conclusions

Introduction(1)• 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 cells.

• 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.

Introduction(2)• 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.

Materials• Nafion® solution Contains 5 wt% of perfluorosulfonate resin (H+ form) and 95 wt% of

isopropanol/water mixture (10:9 weight ratios)

• Tetrabutylzirconate

• Tetraethyl Orthosilicate

• N-methyl-2-pyrrolidone (NMP)

Experimental(1)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 containinghybrid Nafion®–metal oxide nanoparticles was obtained.

Experimental(2)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 78±5m.

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.

XRD

Fig.2. XRD patterns for nanocomposite membranes: Nafion®–zirconia (a), Nafion®–silica (b) and recast Nafion® membrane (c).

a. Nafion®–zirconia b. Nafion®–silica c. recast Nafion®

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.

Water uptake Nafion®–zirconia Nafion®–silica recast Nafion®

Fig.4. Tensile strength of formed membranes with 5% elongation at differenthumidification states: fully hydrated (black) and dry state (gray).

Tensile strength

Fig.5. Proton conductivity of Nafion®–zirconia membrane at 100 ◦Cwithout externalhumidification as a function of time. The zirconia content is 5% in weight.

Proton conductivity

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.

Proton conductivity

Nafion®–zirconia Nafion®–silica recast Nafion®

Conclusions• 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.

Conclusions• Thus, the hybrid membrane developed here has the

potential for PEMFC applications at elevated temperatures

THE END

相對濕度（ relative humidity ） :相對濕度是指是指在某一已知溫度下，空氣所含的實際水汽總量，與該溫度下最大水汽總量之比的數值。一般均以百分率來表示，最低為 0%，最高為 100% 。