Understanding Degradation Pathways of Rutile Oxide Electrocatalysts via Liquid Phase Transmission Electron Microscopy

Oxygen-evolving electrocatalysts in acid, such as iridium oxide and ruthenium oxide, undergo structural changes that result in a loss of activity which necessitates high catalyst loadings of precious noble metal oxides. A fundamental understanding of the structural dynamics at the electrode/electrolyte interface that occur during oxygen evolution is necessary to design the next generation of electrocatalyst materials with improved performance. The Moreno-Hernandez Laboratory utilizes liquid phase transmission electron microscopy to directly observe the stability of single-nanocrystalline and highly faceted metal oxide nanocrystals under anodic conditions in acidic electrolytes. Our studies reveal the distribution of stability relationships between different crystallographic facets for nanocrystalline materials, and enable the direct determination of nanoscale heterogeneity at the single nanocrystal level. Substantial stability differences are observed across multiple nanocrystals, which are correlated to variability in the nanoscale strain present in individual nanocrystals. Structural disorder is also found to result in disparate dissolution behavior on different crystallographic facets, elucidating the nanoscale origin of previously observed structure and stability relationships in metal oxide electrocatalysts. These studies suggest that nanoscale heterogeneity occluded in conventional bulk-scale analysis techniques substantially influences stability under relevant operation conditions, and provide crucial information for the design of resilient electrocatalyst materials.