Clarifying the controversial catalytic active sites of Co3O4 for the oxygen evolution reaction

Insights into the real catalytic active site(s) of promising oxygen evolution reaction (OER) catalysts is significant for the further development of high-performance catalysts. Spinel cobalt oxide (Co3O4), with both tetrahedral (Co2+) and octahedral (Co3+) sites, has been widely studied as an efficient non-precious OER catalyst. However, controversial results still exist regarding its OER performance in determining the active sites from two different tetrahedral and octahedral sites. Here, we have designed size-controllable Co3O4 hexagonal platelets with (111) exposed surfaces only containing tetrahedral Co2+ sites as model catalysts, and systematically investigated the catalytic properties of the tetrahedral sites on the surface of the (111) plane and the octahedral sites on the surface of the (110)-B plane for the OER using density functional theory (DFT) and various characterization methods. The theoretical and experimental results further reveal that the high catalytic activity is based on the existence of octahedral sites in Co3O4, meaning that the octahedral sites are responsible for the OER reaction and have been identified as the dominant active sites of spinel Co3O4.