Oxygen vacancies endow atomic cobalt-palladium oxide clusters with outstanding oxygen reduction reaction activity

ORR pathways on the surface of (a) Co@Pd and (b) CPCo-3 NCs at an open-circuit voltage (OCV) and under potential driven conditions from 1.0 to 0.7 V. In Co@Pd NC, the O2 splitting to 2Oads occurs in the Pd surface the Oads is relocated to the neighbouring oxygen vacancies for conducting the reduction reaction with H2O in CoOXV sites. In CPCo-03, the hydration reaction removes the amorphous CoOX and thus expose the CoPdOXV to the electrolyte from OCV to 1.0V. The PdCoOXV sites are reaction centre for the O2 splitting to 2Oads and collaborate with the neighbouring Pd atoms for completing the ORR.