Topological Trends In Ionic Transport Through Metal-Oxide Composites

Although ionic conductors have been thoroughly investigated, topological features of these materials' nanotextures have been surprisingly overlooked. Here, we report fabrication of a metal-oxide nanocomposite consisting of intertwined phases of platinum (Pt) metal and oxygen-ion conductive cerium oxide (CeO2), i.e., Pt#CeO2. Sectional TEM observations coupled with topological analysis demonstrated that Pt#CeO2 composites having different nanostructures can be classified with a topological measure that corresponds to the phase connectivity of CeO2, namely, the Betti numberbeta0, and another that corresponds to holes of the Pt phase, namely, the Betti numberbeta1. The samples' oxygen ionic conductivity Pt#CeO2 was measured at elevated temperatures in air by alternating current impedance spectroscopy. It was found that the nanostructure changed from a striped appearance to a maze-like appearance as the value ofbeta1 /beta0 decreased. Both the activation energy E and the pre-exponential factorsigma0 for the oxygen ionic conductivity were found to be independent ofbeta1 and exhibited linear, negative correlations withbeta0. The topological connectivity of the ion-conductive CeO2 phase, which was quantified with the Betti numberbeta0, was suitable as a descriptor to correlate the image data of nanostructures with their ionic transport properties.