Electrochemical promotion of a platinum catalyst supported on the high-temperature proton conductor La0.99Sr0.01NbO4−δ

The recently discovered, high-temperature proton conductor, La0.99Sr0.01NbO4−δ, was used as a support for the electrochemical promotion of a platinum catalyst. Ethylene oxidation was used as a probe reaction in the temperature range 350–450 °C. Moderate non-Faradaic rate modification, attributable to a protonic promoting species, occurred under negative polarisation; some permanent promotion was also observed. In oxidative atmospheres, both the image of the reaction mixture and the temperature influenced the type and magnitude of the observed rate modification. Rate-enhancement values of up to ρ = 1.4 and Faradaic-efficiency values approaching Λ = −100 were obtained. Promotion was observed under positive polarisation and relatively dry, oxygen-rich atmospheres suggesting that some oxygen ion conductivity may occur under these conditions. Impedance spectroscopy performed in atmospheres of 4 kPa O2/N2 and of 5 kPa H2/N2 under dry and slightly humidified (0.3 kPa H2O) conditions indicated that the electrical resistivity is heavily dominated by the grain-boundary response in the temperature range of the EPOC studies; much lower grain-boundary impedances in the wetter conditions are likely to be attributable to proton transport.