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 2 interaction that substantially elevates the population of Co 4+ sites for improved water oxidation. We find that phenanthroline only coordinates with Co 2+ forming soluble Co(phenanthroline) 2 (OH) 2 complex in alkaline electrolytes, which can be deposited as amorphous CoO x H y film containing non-bonding phenanthroline upon oxidation of Co 2+ to Co 3+/4+ . This in situ deposited catalyst demonstrates a low overpotential of 216 mV at 10 mA cm -2 and sustainable activity over 1600 h with Faradaic efficiency above 97%. Density functional theory calculations reveal that the presence of phenanthroline can stabilize CoO 2 through the non-covalent interaction and generate polaron-like electronic states at the Co-Co center.