[nanoPost] Nanocomposite membranes for higher temperature operation of PEM fuel cells

University USA

In the Institute they are researching Nafion nanocomposite membranes to increase the proton conductivity and water retention by the membrane at higher temperatures and lower relative humidities and also to improve the thermo-mechanical properties. The main obstacles to commercialization of PEM fuel cells are mostly related to the proton conducting materials, typically solid polymer electrolytes such as Nafion.

These membranes are expensive, mechanically unfavourable at high temperature, and conduct protons only in the presence of water, which limits the fuel cell operating temperature to 80^oC. This in turn results in low fuel cell performance due to low electrode kinetics and less CO tolerance. The operation of fuel cells at high temperature (above 100^oC) provides many advantages such as improved kinetics at the surface of electrode, which is especially important in methanol and CO-containing reformate feeds, and efficient heat and water managements. But, another problem above 100 ^oC is the reduction of electrochemical surface area of the electrodes due to shrinkage of electrolyte (Nafion membrane) in electrodes.

The sol gel approach allows incorporation of inorganic oxides within the pores of Nafion membrane with sub-micronic particle size. The membranes synthesized by this approach were completely transparent and homogenous as compared to membranes prepared by the casting method which were cloudy due to the much larger particles.

The results obtained so far have shown higher conductivity and water uptake as compared to unmodified membrane. At 90^oC and 120^oC, the Nafion- MO2 sol-gel composites exhibited higher water sorption than Nafion membrane, which was their design objective. On the other hand, at 90^oC and 120^oC, the highest conductivity was exhibited by the Nafion- ZrO2 sol-gel composite with a 10 % enhancement at 40 % RH. In addition, the TGA and DMA analysis showed better thermo mechanical properties for composite membranes over Nafion.