Non-covalent ligand-oxide interaction promotes oxygen evolution.

Strategies to generate high-valence metal species capable of oxidizing water often employ composition and coordination tuning of oxide-based catalysts, where strong covalent interactions with metal sites are crucial. However, it remains unexplored whether a relatively weak "non-bonding" interaction between ligands and oxides can mediate the electronic states of metal sites in oxides. Here we present an unusual non-covalent phenanthroline-CoO interaction that substantially elevates the population of Co sites for improved water oxidation. We find that phenanthroline only coordinates with Co forming soluble Co(phenanthroline)(OH) complex in alkaline electrolytes, which can be deposited as amorphous CoOH film containing non-bonding phenanthroline upon oxidation of Co to Co. This in situ deposited catalyst demonstrates a low overpotential of 216 mV at 10 mA cm and sustainable activity over 1600 h with Faradaic efficiency above 97%. Density functional theory calculations reveal that the presence of phenanthroline can stabilize CoO through the non-covalent interaction and generate polaron-like electronic states at the Co-Co center.