Bulk OsO 2 Single Crystals: Superior Catalysts for Water Oxidation

ABSTRACT Although rutile RuO 2 has been a well‐known and almost the best oxygen evolution reaction (OER) catalyst, the OER properties for the similar rutile oxide OsO 2 with the same group element with Ru have been unknown, mainly due to long‐standing synthesis difficulties. In this work, we report the successful synthesis of high‐quality OsO 2 single crystals, and the ground micrometer‐size single crystals are chemically stable in alkaline solutions and exhibit robust OER performance. In sharp contrast, OsO 2 nanopowder reacts quickly with KOH solutions and cannot work for OER. Compared with commercial RuO 2 nanopowder, the OsO 2 single crystals show comparable catalytic current densities, remarkably lower overpotentials at high current densities and better stability. These findings question the universal applicability of nanoscaling and highlight crystal integrity as a key descriptor for achieving stable and efficient OER electrocatalysis.