Tuning the Activation Barrier for Oxygen Exchange on Mixed Conducting Oxide with Fine Control of Transition Metal...

The energy barrier for oxygen exchange at the surface of mixed conducting oxides is a multifactor term that remains difficult to predict with existing models. Here, we describe an experimental approach to fine-tune this barrier on Pr0.1Ce0.9O2-δ used as a model mixed conducting oxide, by adding a minute amount of transition metal impurities to its surface. The variations of the activation barrier for oxygen exchange can be readily correlated with the redox properties of the transition metal oxide, and such a barrier can be decreased by as much as a factor of 2 with more reducible oxide impurities such as Co3O4. We demonstrate that this drop does not originate from the activity of the impurity oxide itself, but rather from the modified surface chemistry of Pr0.1Ce0.9O2-δ induced by the presence of the impurity through the formation of a heterojunction between Pr0.1Ce0.9O2-δ and the transition metals that modifies the energy barrier to oxygen exchange.