Role of UV irradiated Nafion in power enhancement of hydrogen fuel cells

Abstract

The influence of optimum UV ray exposure of pristine Nafion polymer membranes on the improvement of proton conductivity and hydrogen fuel cell performance has been examined. Nafion membranes with thickness 183 μm (117), 90 μm (1035), 50 μm (212) and 25 μm (211) were irradiated with ultraviolet rays with doses in the range 0–250 mJ cm−2 and their proton conductivities have been measured with standard method. The Nafion membranes have also been studied by measuring their water uptake, swelling-ratios and porosity using standard procedures. Hydrogen fuel cells with dual serpentine microchannels with active area 1.9 x 1.6 cm-2 were assembled with anode gas diffusion layer, Nafion membrane, cathode gas diffusion layer and other components. An external humidifier was used to humidify hydrogen for the fuel cell. The experimental Results have shown an increase in the value of Nafion proton conductivity with an optimum UV irradiation which depends on the thickness of Nafion membrane: the optimum doses for peak proton conductivity were 196mJ/cm−2 for Nafion 117, 190mJ/cm−2for Nafion 1035, 180mJ/cm−2 for Nafion 212 and 160mJ/cm−2 for Nafion 211. This enhancement of proton conductivity is because of the optimal photo-crosslinking of –SO3H groups in Nafion. This causes optimum pore-size in Nafion thereby facilitating increased proton-hopping between –SO3H sites in Nafion. Hydrogen fuel cells were developed with pristine as well as with optimal UV irradiated Nafion with thicknesses of 90 and 50 μm. The polarization plots obtained for these devices showed an increase in power densities approximately by a factor of 1.8–2.0 for devices with optimally UV irradiated Nafion. These results indicate that optimal UV irradiation of Nafion is an excellent technique for enhancing power output of hydrogen fuel cells.