Membrane/ionomer proton conductivity effect

Limoges et al. looked at the HOR catalytic activities of a series of heteropolyacids (HPAs) containing Mo and V. The CD is too low (a few mA/cm ) for them to be used as stand-alone anode catalysts, although it should be pointed out that the HPA loading of the anode used in this study was one to two orders of magnitude lower on a molar basis than that of a typical Pt anode. However, HPAs have been shown to be promising proton-conductive membrane/ionomer tillers and effective catalysts for H2O2 decomposition. On this basis, they may eventually become a part of fuel cell electrodes. 

Park HB, Shin HS, Lee YM, Rhim JW (2005) Atmealing effect of sulfonated polysulfone ionomer membranes on proton conductivity and methanol transport. J Membr Sd 247 103-110... 

Luan, Y., Zhang, Y., Zhang, H., Li, L., Li, H., Liu, Y, Anneahng effect of perfluorosul-fonated ionomer membranes on proton conductivity and methanol permeability. J. Appl. 

One of the significant differences between hydrocarbon ionomers and perfluoro-sulfonic acid polymers is add groups. The pKa value of benzenesulfonic acid (PhSOsH) is 2.5 and that of trifluoromethanesulfonic acid (CF3SO3H) is —13. The pKa value was estimated to be ca. 1 for sulfonated polyether ketone and ca. —6 for Nafion membranes [78]. Therefore, the effective proton concentration and proton mobility should be lower in the hydrocarbon ionomer membranes. Without appropriate molecular design such as multiblock copolymer and sulfonic acid clusters as mentioned above, hydrocarbon ionomer membranes lack well-developed ionic channels due to less pronounced hydrophilic and hydrophobic phase separation, which causes the lower proton conductivity at low humidity. 

The group of GKSS Research Center Germany extensively researched the effect of a variety of inorganic nanoparticles on the properties of aromatic ionomer membranes [86-93]. Composite membranes were prepared from silicates and sulfonated poly(ether ketone)s or sulfonated poly(ether ether ketone)s. For DMFC applications, the composite membranes showed promising properties with lower methanol and water permeability and comparable (or higher) proton conductivity compared to the parent polymer membranes. The flux of water and methanol decreased with the increase in content of silicates. 

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