Physical Chemistry Studies of Proton Conduction in Heteropoly Acids

Heteropoly acids (HPA) are promising PEM materials because they have exhibited exceptional proton conductivity not only at ambient temperature, but also at elevated temperatures without external humidification. A library of HPA was synthesized where charge, shape, and hydration state were varied, and the proton conduction structures in the solid state was studied. At ambient conditions, the HPA secondary structure was a "pseudo-liquid" phase and explained the high conductivity of these materials at room temperature. DRIFTS spectra of the free acid HPA showed information on the bonding of water and protons and also showed changes in the outer anion bands as these bonds became more or less involved in bonding to the secondary structure. The activation energy matched the H-bond strength for 21-HAs2W and so presumably all the secondary structure is involved in proton transport and the same is almost true for 21-HP2W. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).