Most transition-metal-based oxygen-evolving catalyst surfaces typically experience irreversible compositional and structural variations during oxygen evolution reaction (OER) in hydrolytic and corrosive alkaline media, degrading the coordination environment of active metal sites into unified (oxy)­hydroxides. Here, we present an in situ electrochemical coordination tuning of cobalt sites for OER in a strong base, where an electrolyzing soluble cobalt-2,2′-bipyridine (Co-bpy) complex partially splits the bpy ligand, leading to the deposition of active Co sites with fine coordination at room temperature. We deposited the Co sites while catalyzing water oxidation at the same condition so that this catalyst can adapt the hostile alkaline condition. This robust coordination environment involving the remaining bpy and generated (oxy)­hydroxide ligands (Co–BH catalyst) sustains the highly improved OER activity over 500 h at 200 mA cm–2, outperforming other fragile Co sites with only (oxy)­hydroxides. In addition, this work presents an efficient tuning of metal coordination environments to in situ generate highly active and stable metal sites in alkaline electrolytes for water splitting.

The iron-based catalysts are promising for the oxygen evolution reaction (OER) in alkaline media, yet the inherent dissolution of high-valent iron species induced performance decay during electrocatalysis remains a critical challenge. Herein, we present a robust iron-based catalyst (Fe-cat) that exhibits a fast ligand-induced regeneration ability, allowing for stable production of oxygen even in a 5.0 M NaOH electrolyte containing iron-2,2′-bipyrimidine (Fe-bpym). Using electrochemical methods and in situ UV–vis and electron paramagnetic resonance, we revealed the coordination configuration transition between the Fe-bpym in electrolytes and the Fe-cat on the electrode during the whole catalyst deposition-solution ligand repairing-catalyst regeneration process. The fast regeneration ability of the active Fe sites endures a long-term OER activity over 200 h with a low overpotential of 320 mV at 1.0 mA cm–2. This study provides an important strategy to design the robust OER catalysts through in situ regeneration of active metal sites on an electrode.

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-CoO2 interaction that substantially elevates the population of Co4+ sites for improved water oxidation. We find that phenanthroline only coordinates with Co2+ forming soluble Co(phenanthroline)2(OH)2 complex in alkaline electrolytes, which can be deposited as amorphous CoOxHy film containing non-bonding phenanthroline upon oxidation of Co2+ to Co3+/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 CoO2 through the non-covalent interaction and generate polaron-like electronic states at the Co-Co center.

Efficient and robust electrocatalysts are required for the oxygen evolution reaction (OER). Photosystem II-inspired synthetic transition metal complexes have shown promising OER activity in water-poor or mild conditions, yet challenges remain in the improvement of current density and performance stability for practical applications in alkaline electrolytes in contrast to solid-state oxide catalysts. Here, we report that a nickel pseudo-complex (bpy) z NiO x H y (bpy = 2,2′-bipyridine) catalyst, which bridges solid oxide and molecular catalysts, exhibits the highest OER activity among nickel-based catalysts with a turnover frequency of 1.1 s–1 at an overpotential of 0.30 volts, even outperforming iron-incorporated nickel (oxy)­hydroxide under an identical nickel mass load. Benefiting from the strong coordination between bpy and nickel, this (bpy) z NiO x H y catalyst exhibits long-term stability in highly alkaline media at 1.0 mA cm–2 for over 200 h and at 20 mA cm–2 for over 60 h. Our findings indicate that dynamically coordinating a small amount of bpy in the catalyst layer efficiently sustains highly active nickel sites for water oxidation, demonstrating a general strategy for improving the activity of transition metal sites with active ligands beyond the incorporation of metal cations to form double-layered hydroxides.