(90d) Oxygen Electrocatalysis Using Layered Mixed Metal Oxides

Oxygen electrocatalysis plays a critical role in a number of important energy conversion and storage systems. Nonstoichiometric, mixed ionic-electronic conducting oxides, such as the first Ruddlesden-Popper (R-P) series of layered oxides (A₂BO₄), have attracted increasing interest due to their high oxygen exchange ability making them suitable for oxygen reduction/evolution. We have recently shown through a combination of quantum chemical density functional theory (DFT) calculations, controlled synthesis of well-defined nanostructures, state-of-the-art characterization techniques (atomic level imaging and electron energy loss spectroscopy), and isotopic labeling kinetic studies that the surface structure of these oxides plays a critical role in their activity toward oxygen reduction. Using a reverse micro-emulsion method, we have demonstrated an approach for synthesizing nanostructured R-P oxide electrocatalysts with controlled surface structure. These nanostructures have been thoroughly characterized using atomic-resolution high angle annular dark field (HAADF) imaging along with electron energy-loss spectroscopy (EELS) performed using an aberration corrected scanning transmission electron microscope (STEM). Kinetic isotopic and electrochemical studies along with DFT calculations are used to develop structure/performance relationships to identify R-P oxides with optimal electrocatalytic activity. These findings pave the way for utilization of nanostructured, layered, nonstoichiometric mixed metal oxides as non-precious metal-based electrocatalysts for oxygen electrocatalysis.