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 number beta 0, and another that corresponds to holes of the Pt phase, namely, the Betti number beta 1. 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 of beta 1 / beta 0 decreased. Both the activation energy E and the pre-exponential factor sigma 0 for the oxygen ionic conductivity were found to be independent of beta 1 and exhibited linear, negative correlations with beta 0. The topological connectivity of the ion-conductive CeO2 phase, which was quantified with the Betti number beta 0, was suitable as a descriptor to correlate the image data of nanostructures with their ionic transport properties.

Automated summary

This study presents the fabrication of metal-oxide nanocomposite Pt#CeO2 and classifies samples with different nanostructures based on topological measures. The nanostructure and oxygen ionic conductivity properties were found to change as the topological measures varied, demonstrating correlations between the structural characteristics and ionic transport properties.