Highly active electrocatalysts for the oxygen evolution reaction (OER) are crucial for improving water electrolysis efficiency. This study examines OER active sites on single-crystal Pt electrodes, revealing that repeated oxidative/reductive potential cycles significantly enhance OER activity on Pt(111), particularly with wider (111) terraces. This activation stems from atomic-sized vacancies created by Pt(111) oxidation/reduction, identified through X-ray diffraction as defects in the second subsurface Pt layer. Bowl-shaped surface roughening, with high-coordination-number Pt atoms at cavity bottoms, further activates the OER.
