Correlation of Low-Index Facets to Active Sites in Micrometer-Sized Polyhedral Pyrochlore Electrocatalyst

Polyhedral structure has attracted attention as a promising morphology of bifunctional electrocatalysts, which is suitable for providing catalytic active facets. However, polyhedral metal oxides have been suffering from control of their morphology. Herein, we develop micrometer-sized polyhedral bismuth ruthenate pyrochlore (P-BRO) for Zn-air batteries, which achieve highly improved catalytic activity by development of (100), (110), and (111) planes regardless of particle size. To clarify the formation mechanism of polyhedral structure, in situ transmission electron microscopy analysis is performed at 1050 °C, resulting in observation of Ostwald ripening and facets formation. Furthermore, we reveal that A- and B-site cations on low-index facets of the P-BRO could mainly contribute to catalytic activity by first-principle calculations. For practical application, we performed Zn-air flow batteries, which could effectively remove precipitated zinc oxide particles on the surface of air electrode, resulting in significantly increased zinc utilization (∼50%) on discharging.