Niobium, Tantalum, and Tungsten Doped Tin Dioxides as Potential Support Materials for Fuel Cell Catalyst Applications

摘要

We report here on potential candidates based on the oxides SnO_2, Nb_2O_5, Ta_2O_5, and WO_3 as alternative support materials for precious metal catalysts with high stability under highly acidic conditions and elevated temperatures as well as sufficient electric conductivity (EC) for application in PEMFCs. To increase the low conductivity of these wide bandgap binary oxides we investigated the mutual doping of these elements and report here on the doping of SnO_2 with W, Nb and Ta in the doping range of 0-15 mol-% metal component. Powder samples were prepared by an optimized sol-gel method based on an acetate route. The samples were characterized by PXRD, TGA as well as 4-point van der Pauw EC measurements. Rietveld refinement of the PXRD pattern over the doping range revealed solid solution formation and anomalies in the lattice parameter changes of the rutiletype structure. As explanation for these observations internal redox reactions between Ta~(5+)/Ta~(4+) and Sn~(4+)/Sn~(2+) were proposed and possibilities to reduce the electrostatic repulsion between cations on introduction of anion vacancies into the crystal structure were discussed.