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.
(© 2023. The Author(s).)